A Randomized Four-Period Cross-Over Phase I Study to Assess Bioavailability, Bioequivalence, and Tolerability of IHL-42X Compared with the Reference Drugs in Healthy Volunteers

Abstract

Background and Objectives

Obstructive sleep apnea (OSA) is a poorly diagnosed, serious, and potentially life-threatening condition that is estimated to impact the lives of up to a billion patients globally. Untreated OSA poses multiple, varied, and serious health risks involving cardiovascular, hepatic, metabolic, endocrine, neurological, and mental health indications. Effective management of OSA currently relies on device-based positive airway pressure (PAP), but poor adherence significantly affects clinical management and long-term use. The preliminary proof-of-concept study demonstrated the combination of dronabinol (DRN) and acetazolamide (ACZ) for treatment of OSA. IHL-42X is a proprietary formulation comprised of a solid, film coated ACZ tablet contained within a DRN-sesame oil solution gel cap. Each IHL-42X gel cap contained 5 mg of DRN and 250 mg of ACZ. This study assessed the bioavailability, food effect, and bioequivalence of IHL-42X compared with the reference listed drugs for DRN and ACZ.

Methods

The study was a four-period crossover study in healthy volunteers (HVs) at two sites in Australia. A total of 125 participants were recruited and assigned to one of four treatment sequences (A-B-C-D, B-D-C-A, C-A-D-B, and D-C-B-A: A = DRN 5 mg, fasted; B = ACZ 250 mg, fasted; C = IHL-42X (5 mg DRN + 250 mg ACZ), fasted; and D = IHL-42X (5 mg DRN + 250 mg ACZ), fed), with a minimum 7-day washout period between doses. Safety assessments included vital signs, electrocardiogram (ECG) parameters, and clinical laboratory parameters. Plasma concentrations of ACZ and tetrahydrocannabinol (THC) plus major metabolites of THC, carboxy-THC (COOH-THC), and hydroxy-THC (OH-THC) were conducted on blood samples taken pre-dose and post-dose at 0.08, 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 12, 16, 24, 36, and 48 were determined using liquid chromatography-tandem mass spectrometry. Analysis of variance (ANOVA) with Dunnet’s adjustment was used on log-transformed PK variables with sequence, treatment, period, and participants nested within a sequence as fixed effects to determine bioequivalence. Bioequivalence (BE) for ACZ, THC, OH-THC, and COOH-THC for IHL-42X relative to reference listed drugs (RLDs) was concluded if the 90% CI around the geometric least squares (LS) mean ratio fell within the predefined limits (0.80 and 1.25) for the maximum plasma concentration (C_max), area under curve from zero to last measurable concentration (AUC_0–last), and AUC from zero extrapolated to infinity (AUC_0–inf). All adverse events (AE) terms were coded using MedDRA^® Version 26.0.

Results

Overall IHL-42X was well tolerated in both fasted and fed states with no serious adverse events (SAEs) reported during the study. At least one treatment-emergent adverse event (TEAE) was reported in 70 (57.4%), 63 (52.1%), and 45 (37.8%) subjects in the IHL-42X, DRN, and ACZ groups under fasted conditions, respectively, and in 70 (58.8%) subjects in the IHL-42X group under fed conditions. All but one of the TEAEs were mild or moderate in severity. The BE for ACZ was concluded for IHL-42X fasted versus ACZ based on AUC_0–inf (0.910 [90% CI 0.865, 0.958]) and AUC_0–last (0.882 [90% CI 0.838, 0.929]) but not for the C_max (0.597 [90% CI 0.550, 0.647]). For THC, BE was concluded for AUC_0–inf (0.948 [90% CI 0.822, 1.093]) but not for C_max (0.829 [90% CI 0.705, 0.975]) or AUC_0–last (0.877 [90% CI 0.762, 1.010]).

Conclusions

IHL-42X was well tolerated in both fasted and fed states with an increased overall exposure to THC when administered with food. No serious adverse events were reported during the study. The PK profiles IHL-42X were similar to the RLDs for DRN and ACZ, selected analytes, and PK parameters. The data support bioavailability of IHL-42X, confirming oral delivery of both DRN and ACZ from the formulations.

Trial Registration

NCT05857384 (Posted 12/05/2023).

Key Points

IHL-42X was generally well tolerated and biovailable when administered with or without food.

Some parameters, such as maximum plasma concentration (Cmax) for acetazolamide and area under curve from zero to last measurable concentration (AUC0–last) for tetrahydrocannabinol, did not meet bioequivalence criteria.

These findings support the oral delivery of both DRN and ACZ from the formulations.

Introduction

Obstructive sleep apnea (OSA) is characterized by frequent interruptions to breathing during sleep, which leads to repeated hypoxia and awakenings, as well as poor sleep quality [1]. Breathing interruptions are caused by partial or complete collapse of the upper airway [2]. In the USA, OSA has a prevalence rate of 24% and 9% in men and women, respectively [2]. Rates as high as 90% and 78% among men and women, respectively, in older populations are reported [3]. OSA has negative consequences on members of the work force across all sectors, including active military members [4, 5], as it is directly associated with cognitive, mental health and functional impairment [6, 7], extreme daytime hypersomnolence, fatal automobile accidents [8, 9], social stigma, and consequent chronic morbidity and mortality [10, 11]. The burden of OSA is predicted to increase dramatically due to high levels of obesity, aging, and comorbidities [11–14]. OSA has also been strongly associated with life-threatening disorders including hypertension, cardiac disorders, stroke, diabetes, post-traumatic stress disorder (PTSD), mental health, and associated cause-specific morbidity and mortality [15–17]. Cumulatively, untreated OSA costs the USA alone approximately $150 billion per year [18–20]. Effective management of OSA was associated with favorable economic outcomes at all levels of service delivery [21, 22]. This has relied on two main treatment categories: the device-based positive airway pressure (PAP) and non-PAP therapies [23]. The former has been standard of care for more than 40 years due to the demonstrated effectiveness on OSA and reductions in comorbidities associated with OSA including incident hypertension and cardiovascular events, as well as overall morbidity and all-cause mortality [24, 25]. The burden of OSA is often exacerbated by poor diagnosis and poor adherence (estimated at 30–60%) to device-based therapy [26], as well as the disproportionate benefits to patients with varying disease-severity range [27]. Oral pharmacotherapeutic alternatives exploring the convenience of oral dosing to overcome compliance and adherence issues observed with PAP would offer a more consistent benefit and improve overall quality of life in patients with OSA. Targeting critical pathophysiological mechanisms such as intermittent hypoxia, mild CO₂ retention, increased sympathetic activity, systemic inflammation, and unstable hemodynamic responses during sleep might provide OSA clinical benefits [28]. The combination of dronabinol (DRN) and acetazolamide (ACZ) has shown promise for the treatment of OSA in a phase 2 clinical trial [29]. The success of the combination led to development of IHL-42X, a fixed dose combination (FDC) of DRN and ACZ as an oral pharmacotherapy for all patients with OSA. The IHL-42X drug product consists of a film-coated solid ACZ tablet within a soft gel capsule with a liquid formulation of DRN. This combination is formulated using the UniGel™, a proprietary technology to harness the synergistic and complimentary clinical benefits of DRN and ACZ [29]. This current clinical trial aimed to determine the bioavailability of DRN and ACZ from a single dose IHL-42X comparison with their respective reference drugs as listed in the Food and Drug Administration (FDA) Orange Book, Marinol and Taro acetazolamide (ACZ) tablet, under fasted conditions as well as comparing the effect of administration in a fed state on the bioavailability of both drugs. The study was conducted in healthy volunteers.

Methods

Compliance with Ethical Standards

The requirements for the conduct of clinical trials in accordance with the applicable regulations of the Australian Therapeutic Goods Administration (TGA) under the Clinical Trial Notification (CTN) scheme were met before the commencement of this study. The clinical trial was publicly registered on the public registry ClinicalTrials.gov website on 12/05/2023 (NCT05857384).

This study was carried out according to the principles of the Declaration of Helsinki, the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) Guideline for Good Clinical Practice (GCP) E6(R2) (2016) (as adopted in Australia), and the National Health and Medical Research Council National Statement on Ethical Conduct in Human Research (2007, incorporating all updates). The study protocol was approved by Bellberry Human Research and ethics committee (123 Glen Osmond Road, Eastwood, 5063, South Australia). This study was registered on clinicaltrials.gov NCT05857384 prior to recruitment of any subjects.

Investigational Product

The IHL-42X drug product consists of a film coated ACZ tablet contained inside a soft gelatin capsule filled with DRN in sesame oil. These capsules are size 20 oblong softgel (1000–1100 cc) and opaque brown in color. Manufacturing of this dose form is accomplished using UniGel^™, a proprietary technology developed by ProCaps^® (Barranquilla, Colombia). The DRN used in manufacture IHL-42X is of synthetic origin, that is, it is not extracted from botanical material. Reference listed drugs (RLD) Marinol and Taro ACZ were sourced from commercial pharmaceutical suppliers. Subjects in the 5 mg DRN group received two capsules of 2.5 mg of Marinol while those in the ACZ group received a single 250 mg Taro ACZ tablet.

Participants

Consent to participate in the study was obtained from all potential participants. Eligible participants as per protocol inclusion and exclusion criteria following a 28-day screening period were enrolled. The study included: adult male and female volunteers aged 18 to ≤ 65 years; body mass index (BMI) ≥ 18 to ≤ 32; with no known allergic reaction to cannabis products with previous use and sesame oil; no history of past substance abuse or current abuse of illicit drugs as defined by a negative Drugs of Abuse (DOA) test at screening; physically well with no severe psychiatric, cardiac, renal, endocrine, gastrointestinal, bleeding, thyroid, cholesterol, or hypertension disorders; and willingness to adhere to approved male and females contraception.

Potential participants with a history of cardiac disease or clinically significant arrythmia, psychiatric illness, suicidal ideation, or meeting other criteria as per protocol were excluded. In the food effect arm, participants consumed at least 80% of a standard high fat meal comprised of 50% of total caloric content and between 800 and 1000 high calorie breakfast 30 min prior to administration of IP.

Treatment Groups

The study enrolled 125 participants across the 4 sequence groups, which allocated interventions in 4 periods, using a Latin square design. This was an open-label study where randomization sequences were generated using paper-based central blocked fixed methodology at a 1:1:1:1 ratio across the four treatment groups. Participants were assigned to treatment sequences as follows: 32 participants received sequence 1, 30 participants received sequence 2, 32 participants received sequence 3, and 31 participants received sequence 4. All four groups received all four treatments in different orders, as defined by period 1, period 2, period 3, and period 4 (Table 1). All screened participants received a unique screening number. Eligible and enrolled subjects were assigned a randomization number prior to dosing and were randomized to one of the four treatment groups (Fig. 1).

Table 1.

Latin square group design and treatment periods

	Period 1	Period 2	Period 3	Period 4
Group 1	A	B	C	D
Group 2	B	D	C	A
Group 3	C	A	D	B
Group 4	D	C	B	A

A, dronabinol 5 mg, fasted; B, acetazolamide 250 mg, fasted; C, IHL-42X (5 mg dronabinol, 250 mg acetazolamide), fasted; D, IHL-42X (5 mg dronabinol, 250 mg acetazolamide), fed.

Fig. 1.

Consort schematic demonstrating IHL-42X phase 1 trial overview

Tolerability and Safety Analysis

Baseline analysis of body weight, vital signs, physical examination, clinical laboratory, and electrocardiogram (ECG) data were defined as the last evaluation done before the first administration of study drug for each participant. Vital sign assessments were conducted at the screening visit and throughout each treatment period from visit day − 1 at pre-dose, 2 h post-dose, and 48 h post-dose. These included heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), temperature, and respiratory rate in the supine position after a period of 5 min at rest. Vital sign assessments were repeated once to confirm any out-of-range results or at the discretion of the investigator. Pre-dose vital sign assessments had a − 30-min window while a ± 10-min window was allowed from 2 to 48 h post-dose. The 12-lead ECGs were performed in triplicate at screening, at pre-dose visit day − 1, 8 h, and 48 h post-dose for each treatment period. The analyzed ECG parameters, including PR interval, QTS, QTcF, and HR, were compared with normal reference ranges. For routine safety blood analysis, samples were collected during screening, at visit day − 1, 4 h, and 24 h post-dose for each treatment period for biochemistry and hematology evaluations with a ± 10-min window for 4–24-h post-dose collections. The lab samples were collected, handled, and processed as per Australian National Association of Testing Authorities (NATA) guidelines. Laboratory data were compared with normal reference ranges as per validated procedures. Clinically significant abnormal results were noted and recorded per participant.

All the AEs were coded using the current version of the Medical Dictionary for Regulatory Activities by system organ class (SOC) and preferred term, classified from verbatim terms. The number of TEAEs and serious TEAEs as well as the number and percentage of participants with TEAEs and serious TEAEs, were summarized by SOC and preferred term and tabulated for each treatment. The safety conclusions were based on the incidence, severity, and relationship of AEs, body weight, vital signs, physical examination findings, clinical laboratory results, and ECGs. Observed values and changes from baseline for vital signs and body weight were summarized at each scheduled timepoint for each treatment. Any clinically significant findings were reported as adverse events (AEs).

Pharmacokinetic Analysis

To assess the bioequivalence and bioavailability of the investigational product (IP), analyses of plasma ACZ and tetrahydrocannabinol (THC) plus its major metabolites of THC, carboxy-THC (COOH-THC), and hydroxy-THC (OH-THC) were conducted on blood samples taken at pre-dose and post-dose at 0.08-, 0.25-, 0.5-, 1-, 1.5-, 2-, 2.5-, 3-, 3.5-, 4-, 6-, 8-, 12-, 16-, 24-, 36-, and 48-h timepoints for each treatment period. The plasma from pharmacokinetic (PK) blood samples was analyzed using a validated bioanalytical method (Agilex, SA, Australia). Briefly, samples were extracted and injected into a high-performance liquid chromatography (HPLC) system coupled to a Sciex API/4000/6500 mass detector following validated methods for both ACZ and THC with respective metabolites. The THC, COOH-THC, and OH-THC and their respective deuterated internal standards (IS) from human plasma were extracted using protein precipitation followed by solid phase extraction. The method extracted ACZ and the internal standard (IS) from human plasma using supported liquid extraction (SLE) procedure. The analytes were separated by HPLC on a Phenomenex Luna Omega 1.6 µm Polar C18 100A° 50 × 2.1 mm, and the eluates monitored by a Sciex APl4000 MS/MS detector in positive MRM mode.

For the plasma concentration, the number of non-missing values, number of below the limit of quantification (BLQ) values, arithmetic mean, SD, median, minimum, maximum, coefficient of variation (CV%), geometric mean, and geometric coefficient of variation (geo CV%) values were presented. The PK parameters were, where possible, determined from the plasma concentrations of ACZ, THC, COOH-THC, and OH-THC using noncompartmental methods via Phoenix WinNonlin^® Version 8.3 or higher. Timepoint samples for PK analysis were collected as per study design and summarized below per individual analytes (Table 2). Bioanalytical methods were compliant with FDA Guidance for Industry: bioanalytical method validation and EMA Guideline on Bioanalytical Method Validation [30].

Table 2.

Pharmacokinetic parameters

Parameter	Definition
Cmax	Maximum plasma concentration obtained directly from the data without interpolation.
Tmax	Time to reach Cmax directly from the data without interpolation.
AUC0-last	The area under the drug concentration-time curve, from time zero to time of the last measurable concentration, calculated by the “linear up and log down” method.
AUC0-inf	Area under the drug concentration-time curve, from time zero extrapolated to infinity.
AUC0-12h	Area under the drug concentration-time curve, from time 0 h to 12 h, calculated by the “linear up and log down” method.
AUC0-24h	Area under the drug concentration-time curve, from time 0 h to 24 h, calculated by the “linear up and log down” method.
AUC%extrap	The percentage of the AUC that was extrapolated beyond the last observed data point.
t1/2	Apparent plasma terminal elimination half-life.
λz or Kel	The apparent terminal elimination rate constant.
CL/F	Apparent total plasma clearance.
Vz/F	Apparent terminal volume of distribution.

K_el, elimination rate constant. Values for λ_z, t_1/2, AUC_0-inf, AUC_%extrap, CL/F, and Vz/F were not reported for cases that did not exhibit a terminal log-linear phase in the concentration versus time profile.

Statistical Analysis

Sample size determination was done based on estimated published variability of PK parameters of DRN and ACZ. The coefficient of variation (CV) for C_max and AUC_0–t were used. To reflect the highest variability likely to be observed across fasted and fed conditions and the two drugs, a CV value of 0.58 was chosen for sample size calculations. In an equivalence test of means using two one-sided tests on log-normal data from a four-period cross-over design, a total sample size of 102 achieves 80% power at a 5% significance level (comparable to a 90% confidence interval) when the actual ratio of the means is 1, the CV on the original, unlogged scale is 0.58, and the equivalence limits of the mean ratio are 0.8 and 1.25, corresponding to ln(0.8) and ln(1.25) of − 0.223144 and 0.223144, respectively. Anticipating a 10% dropout rate, 114 participants needed to be enrolled to obtain a final sample size of 102 participants. Therefore, a total of at least 116 healthy volunteers needed to be enrolled across the four treatment sequences. The study data were summarized using descriptive statistics (number of nonmissing observations, mean, median, standard deviation, minimum and maximum) or frequency counts and percentages, as appropriate to the type of data. The safety analysis set (SS) included all subjects who received a dose of any of the treatments and completed at least one post-dose safety assessment.

The PK analysis set included all subjects in the safety analysis set who had sufficient plasma concentration to derive at least one PK parameter. Analysis of plasma THC and ACZ concentration data and THC’s major metabolites, COOH-THC and OH-THC, were conducted. The primary analytes for bioequivalence determination were; Taro acetazolamide—ACZ and for Marinol—THC, while the OH-THC was a secondary analyte; and COOH-THC a surrogate for analytical and safety characterization. Individual participant plasma analyte concentrations were listed and summarized at each timepoint by treatment. Individual participant and mean (by treatment) plasma concentration-time profiles were presented graphically with concentration displayed on linear and logarithmic scales. The following C_max, T_max, AUC_0–last, and AUC_0–inf were compared between treatments. The comparison of exposure between treatments was performed using analysis of variance (ANOVA) of log-transformed values of key exposure PK parameters (C_max, AUC_0–last, AUC_0–inf) for each treatment. From this, the geometric least-squares mean test/reference ratio for each exposure PK parameter was calculated, along with the two-sided 90% confidence interval for each ratio: with IHL-42X as the test treatments and Marinol and Taro ACZ as the reference treatments. The analysis was performed using ANOVA with the term treatment.

To assess the bioequivalence between the test treatment (IHL-42X fasted) compared with the reference treatments (dronabinol fasted and acetazolamide fasted), an analysis of variance (ANOVA) model was used on log-transformed PK variables (C_max, AUC_0–last, and AUC_0–inf) with sequence, treatment, period, and participants nested within a sequence as fixed effects. Dunnett’s method was applied to adjust for multiple comparisons. A 90% confidence interval (CI) was constructed to compare the test treatment with each of the reference treatments. Least squares (LS) estimate of treatment effects was calculated and a 90% CI for the treatment difference was computed. The treatment difference and its 90% CI was exponentiated (back transformed) to obtain the ratio of the geometric means between the test and reference products and its CI. Average bioequivalence could be claimed if the 90% CIs for ratio of the geometric means of C_max, AUC_0–last, and AUC_0–inf were completely within the range 80–125%. In addition, comparisons of PK parameters were conducted between IHL-42X fasted and IHL-42X fed. These comparisons were performed using the same ANOVA model, although no attempt was made to draw conclusions regarding bioequivalence. The PK parameters estimated for each treatment period from pre-dose on day 1 to 48 h post-dose are provided in Table 2.

Results

Baseline Characteristics

A total of 125 participants were enrolled in the study and randomized across the four sequential treatment periods or sequences (n = 32, 30, 32, and 31), respectively (Table 1). Overall, 114 of 125 (91.2%) participants completed the study. A total of 11 (8.8%) participants did not complete the study, with 5 (4.0%) due to adverse events (AEs) such as dizziness, delirium, and akathisia; 3 (2.4%) due to voluntary participant withdrawal; and 3 (2.4%) due to other reasons such as poor vein access, withdrawal by physician (infections), and overseas holiday. The baseline demographic data including age, BMI, sex, race, and ethnicity were collected at screening. The median age of participants was 30.0 (range 18–65) years, mean BMI was 24.97 (SD 3.20) kg/m², gender distribution was 70 of 125 (56.0%) male and 55 of 125 (44.0%) female, 84 of 125 (67.2%) white or 19 (15.2%) Asian and the ethnicity was reported as 93 of 125 (74.4%) not Hispanic or Latino. There was an uneven distribution of gender, with male participants exceeding female participants by 15 (12.0%). Baseline characteristics are summarized in Table 3.

Table 3.

Demographics and baseline characteristics (safety analysis set)

Parameter	Sequence 1 (N = 32)	Sequence 2 (N = 30)	Sequence 3 (N = 32)	Sequence 4 (N = 31)	Overall (N = 125)
Age (years) at screening
n	32	30	32	31	125
Mean	30.3	35.5	30.8	35.0	32.9
SD	11.4	14.0	9.3	11.3	11.7
Median	26.5	30.5	29.5	31.0	30.0
Minimum	18	19	18	21	18
Maximum	63	65	52	62	65
Sex n (%)
Female	10 (31.3%)	11 (36.7%)	18 (56.3%)	16 (51.6%)	55 (44.0%)
Male	22 (68.8%)	19 (63.3%)	14 (43.8%)	15 (48.4%)	70 (56.0%)
Race n (%)
American Indian or Alaska Native	1 (3.1%)	2 (6.7%)	4 (12.5%)	0	7 (5.6%)
Asian	6 (18.8%)	4 (13.3%)	4 (12.5%)	5 (16.1%)	19 (15.2%)
Black or African American	3 (9.4%)	0	0	0	3 (2.4%)
Native Hawaiian or other Pacific Islander	0	0	0	1 (3.2%)	1 (0.8%)
White	19 (59.4%)	21 (70.0%)	22 (68.8%)	22 (71.0%)	84 (67.2%)
Unknown	0	0	0	1 (3.2%)	1 (0.8%)
Other	1 (3.1%)	2 (6.7%)	2 (6.3%)	1 (3.2%)	6 (4.8%)
Multiple	2 (6.3%)	1 (3.3%)	0	1 (3.2%)	4 (3.2%)
Ethnicity n (%)
Hispanic or Latino	5 (15.6%)	7 (23.3%)	8 (25.0%)	9 (29.0%)	29 (23.2%)
Not Hispanic or Latino	25 (78.1%)	22 (73.3%)	24 (75.0%)	22 (71.0%)	93 (74.4%)
Unknown	2 (6.3%)	1 (3.3%)	0	0	3 (2.4%)
BMI (kg/m2) at screening
n	32	30	32	31	125
Mean	24.12	25.00	25.47	25.30	24.97
SD	2.73	3.41	3.21	3.38	3.20
Median	23.85	24.50	25.00	25.40	24.50
Minimum	19.5	18.9	19.2	18.9	18.9
Maximum	30.7	31.3	31.8	31.2	31.8

BMI body mass index, N number of participants in group, n number of participants with observations, SD standard deviation

The medical history was consistent with a healthy adult population, and no conditions of clinical concern were reported. Prior medications were defined as any medication where the use was stopped prior to day − 30 of the study. Overall, 8 of 125 (6.4%) participants reported prior medication use. The only prior medications reported by more than one participant were coronavirus disease 2019 (COVID-19) vaccines (7 participants [5.6%]). All participants had negative pre-dose urine drug screen results on day − 1. All post-dose urine drug screen results were negative except for 47 positive results for THC at day 3 or unscheduled visits. Positive post-dose results for THC were expected due to the THC content of the IP. All participants had negative alcohol breath test results at screening and on day − 1 of each treatment period (Listing 16.2.4.5), and negative serology at screening. All women of childbearing potential (WOCBP) had negative pregnancy test results at screening and on day −1. Follicle-stimulating hormone (FSH) tests were conducted for four participants and all results were ≥ 30 IU/L. No participants met exclusion criteria for Generalised Anxiety Disorder (GAD)-7 score ≥ 15, Major Depression Inventory (MDI) score ≥ 31, or Columbia-Suicide Severity Rating Scale (C-SSRS) score ≥ 4 at screening.

Safety and Tolerability of IHL-42X

All 125 (100%) participants were included in the safety analysis population. The adverse events (AE) verbatim terms were coded using MedDRA^® Version 26.0. All AE summaries were restricted to treatment-emergent AEs (TEAEs) only, defined as AEs that occurred following the administration of IP in each treatment period. Participants experiencing AEs that persisted across the treatment periods without increasing in severity were exclusively included and counted within the corresponding treatment period where the AE initially started. AEs occurring prior to the first dose of IP were listed but not included in any tabulations. Participants were counted only once for each System Organ Class (SOC) and PT (categorical descriptive analysis). The participants were assessed for AEs from the time of consent until the completion of the End of Study (EOS) visit.

Treatment-Emergent Adverse Events

An overall summary of TEAEs (AEs that occurred following the administration of IP in each treatment period) for each treatment is provided in Table 4. Overall, at least one TEAE was reported for 107 of 125 (85.6%) participants. At least one TEAE was reported for 63 (52.1%) participants who received DRN, 45 (37.8%) participants who received ACZ, 70 (57.4%) participants who received IHL-42X fasted, and 70 (58.8%) participants who received IHL-42X fed. One participant (0.8%) who received IHL-42X fasted treatment had severe anxiety TEAE on day 15, however, the participant recovered from the event within 2 h. At least one treatment-related TEAE was reported for 54 (44.6%) participants who received DRN, 26 (21.8%) participants who received ACZ, 55 (45.1%) participants who received IHL-42X fasted, and 61 (51.3%) participants who received IHL-42X fed. Four (3.3%) participants who received IHL-42X fasted and two (1.7%) participants (one who had received both IHL-42X fasted and fed treatment) who received IHL-42X fed had TEAEs leading to study discontinuation. There were no SAEs reported for any participant.

Table 4.

Overall summary of treatment-emergent adverse events (safety analysis set)

	A: Dronabinol 5 mg fasted (N = 121) n (%) E	B: Acetazolamide 250 mg fasted (N = 119) n (%) E	C: IHL-42X-Fasted (N = 122) n (%) E	D: IHL-42X-Fed (N = 119) n (%) E	Overall (N = 125) n (%) E
Number (%) of participants reporting ≥ 1
TEAE	63 (52.1%) 130	45 (37.8%) 65	70 (57.4%) 162	70 (58.8%) 142	107 (85.6%) 499
Serious TEAE	0	0	0	0	0
Severe TEAEa	0	0	1 (0.8%) 1	0	1 (0.8%) 1
Related TEAEb	54 (44.6%) 98	26 (21.8%) 31	55 (45.1%) 114	61 (51.3%) 119	97 (77.6%) 362
TEAE leading to study discontinuation	0	0	4 (3.3%) 8	2 (1.7%) 4	5 (4.0%) 12

E number of events, IP investigational product, N number of participants in group, n number of participants with observations, TEAE treatment-emergent adverse event

^aSevere TEAE was defined as TEAE with severity of severe or life threatening or death

^bRelated TEAE was defined as relationship to IP reported as possible, probable or definite

The TEAEs for each treatment classified by MedDRA^® System Organ Class (SOC) and individual preferred term (PT) are provided in Table 5. In the Nervous System Disorders SOC, the incidence of TEAEs was similar for DRN (44 [36.4%] participants), IHL-42X fasted (45 [36.9%] participants), and IHL-42X fed (49 [41.2%] participants), and lowest for ACZ (27 [22.7%] participants). In the Psychiatric Disorders SOC, the incidence of TEAEs was similar for IHL-42X fasted (24 [19.7%] participants) and IHL-42X fed (22 [18.5%] participants), and slightly lower for DRN (15 [12.4%] participants); there were no TEAEs in the Psychiatric Disorders SOC for ACZ.

Table 5.

Commonly reported treatment-emergent adverse events (preferred terms in ≥ 10% of participants for any treatment) (safety analysis set)

System organ class preferred term	A: Dronabinol 5 mg fasted (N = 121) n (%) E	B: Acetazolamide 250 mg fasted (N = 119) n (%) E	C: IHL-42X Fasted (N = 122) n (%) E	D: IHL-42X Fed (N = 119) n (%) E	Overall (N = 125) n (%) E
Participants with ≥ 1 TEAE	63 (52.1%) 130	45 (37.8%) 65	70 (57.4%) 162	70 (58.8%) 142	107 (85.6%) 499
Nervous system disorders	44 (36.4%) 66	27 (22.7%) 30	45 (36.9%) 65	49 (41.2%) 68	89 (71.2%) 229
Somnolence	23 (19.0%) 24	10 (8.4%) 10	18 (14.8%) 19	25 (21.0%) 25	47 (37.6%) 78
Headache	11 (9.1%) 12	12 (10.1%) 12	16 (13.1%) 17	12 (10.1%) 13	35 (28.0%) 54
Dizziness	12 (9.9%) 12	3 (2.5%) 3	9 (7.4%) 9	12 (10.1%) 12	28 (22.4%) 36
Psychiatric disorders	15 (12.4%) 15	0	24 (19.7%) 27	22 (18.5%) 26	41 (32.8%) 68
Euphoric mood	14 (11.6%) 14	0	17 (13.9%) 18	17 (14.3%) 17	32 (25.6%) 49

TEAEs were defined as AEs that occurred following the administration of IP

E number of events, IP investigational product, N number of participants in group, n number of participants with observations, TEAE treatment-emergent adverse event

By PT, the most commonly reported TEAEs (occurring in at least 10% of participants for any treatment) by treatment were: DRN: somnolence in 23 (19.0%) participants and euphoric mood in 14 (11.6%) participants; ACZ: headache in 12 (10.1%) participants; IHL-42X fasted: somnolence in 18 (14.8%) participants, headache in 16 (13.1%) participants, and euphoric mood in 17 (13.9%) participants; and IHL-42X fed: somnolence in 25 (21.0%) participants, headache and dizziness each in 12 (10.1%) participants, and euphoric mood in 17 (14.3%) participants (Table 5). Overall, most participants had TEAEs that were mild (107 of 125 [85.6%] participants). Moderate TEAEs were reported for 27 of 125 (21.6%) participants.

Treatment-Related Treatment-Emergent Adverse Events

Treatment-related TEAEs were defined as TEAEs evaluated as possibly, probably, or definitely related to the IP. A summary of the most commonly reported treatment related TEAEs is provided in Table 5. Overall, 83 of 125 (66.4%) participants had TEAEs that were deemed possibly related (Table 6). By PT, the most common possibly related TEAEs (occurring in at least 5% of participants for any treatment) were: somnolence in 17 (14.0%) participants and headache in 7 (5.8%) participants; somnolence in 6 (5.0%) participants and headache in 9 (7.6%) participants; somnolence in 12 (9.8%) participants and headache in 9 (7.4%) participants; and somnolence in 17 (14.3%) participants, headache in 11 (9.2%) participants, and dizziness in 8 (6.7%) participants in the DRN, ACZ, IHL-42X fasted, and IHL-42X fed arms, respectively. Overall, 13 of 125 (10.4%) participants had TEAEs that were deemed definitely related and 53 (42.4%) TEAEs deemed probably related. By PT, there were no definitely related TEAEs that occurred in at least 5% of participants for any treatment.

Table 6.

Commonly reported treatment-related treatment-emergent adverse events (preferred terms in ≥ 5% of participants for any treatment) (safety analysis set)

Preferred term relationship	A: Dronabinol 5 mg fasted (N = 121) n (%) E	B: Acetazolamide 250 mg fasted (N = 119) n (%) E	C: IHL-42X fasted (N = 122) n (%) E	D: IHL-42X fed (N = 119) n (%) E	Overall (N = 125) n (%) E
Participants with ≥ 1 TEAE
Possibly related	38 (31.4%) 57	22 (18.5%) 26	37 (30.3%) 65	46 (38.7%) 71	83 (66.4%) 219
Probably related	23 (19.0%) 38	5 (4.2%) 5	26 (21.3%) 38	29 (24.4%) 43	53 (42.4%) 124
Definitely related	3 (2.5%) 3	0	8 (6.6%) 11	4 (3.4%) 5	13 (10.4%) 19
Somnolence
Possibly related	17 (14.0%) 18	6 (5.0%) 6	12 (9.8%) 13	17 (14.3%) 17	36 (28.8%) 54
Probably related	5 (4.1%) 5	4 (3.4%) 4	5 (4.1%) 5	7 (5.9%) 7	15 (12.0%) 21
Definitely related	1 (0.8%) 1	0	1 (0.8%) 1	1 (0.8%) 1	3 (2.4%) 3
Headache
Possibly related	7 (5.8%) 7	9 (7.6%) 9	9 (7.4%) 9	11 (9.2%) 12	27 (21.6%) 37
Probably related	1 (0.8%) 1	0	1 (0.8%) 1	0	2 (1.6%) 2
Definitely related	0	0	0	0	0
Dizziness
Possibly related	3 (2.5%) 3	2 (1.7%) 2	4 (3.3%) 4	8 (6.7%) 8	16 (12.8%) 17
Probably related	6 (5.0%) 6	0	4 (3.3%) 4	4 (3.4%) 4	11 (8.8%) 14
Definitely related	1 (0.8%) 1	0	0	0	1 (0.8%) 1
Euphoric mood
Possibly related	0	0	2 (1.6%) 2	0	2 (1.6%) 2
Probably related	13 (10.7%) 13	0	9 (7.4%) 9	13 (10.9%) 13	24 (19.2%) 35
Definitely related	1 (0.8%) 1	0	6 (4.9%) 7	4 (3.4%) 4	9 (7.2%) 12

Treatment-related TEAEs were defined as TEAEs evaluated as possibly, probably, or definitely related to IP

E number of events, IP investigational product, N number of participants in group, n number of participants with observations, TEAE treatment-emergent adverse event

Vital Signs, Physical Findings, and Other Observations Related to Safety

Vital signs, physical, electrocardiogram (ECG) results and concomitant medications use at each timepoint were captured. For each treatment, minor mean decreases in systolic blood pressure (ranging from − 1.3 to 2.7 mmHg by treatment) and diastolic blood pressure (− 0.6 to − 3.6 mmHg) were seen on day 1 and had resolved toward baseline by day 3. No participants had scheduled systolic or diastolic blood pressure findings considered abnormal clinically significant. A TEAE of hypotension (SBP [65 mmHg] versus DBP [43 mmHg]) was reported for 1 (0.8%) participant for IHL-42X fed. A mean increase in heart rate on day 1 was seen with IHL-42X fed (+ 8.0 beats per min [bpm]), IHL-42X fasted (+ 2.1 bpm), and DRN (+ 2.9 bpm); a slight mean decrease was seen with ACZ (− 1.4 bpm). An abnormal clinically significant heart rate (+ 8.0 bpm) was recorded for one (0.8%) participant with IHL-42X fed treatment, which was reported as a TEAE of mild palpitations considered possibly related. Overall, TEAEs of palpitations were reported for one (0.8%) participant for DRN, two (1.6%) participants for IHL-42X fasted, and three (2.5%) participants for IHL-42X fed. There were no clinically significant physical examination results during treatment that were reported. No safety concerns were identified from mean ECG parameter values for any treatment. The Columbia-Suicide Severity Rating Scale (C-SSRS) questionnaire results at screening and period 4 day 3 (EOS) did not identify suicidal ideation during the study.

In terms of concomitant medications use, overall, 58 of 125 (46.4%) participants received at least one concomitant medication. The most common concomitant medication by PT (≥ 10% of participants) was paracetamol, which was used by 30 (24.0%) participants. Paracetamol was used by 8 of 32 (25.0%) participants in sequence 1, 8 of 30 (26.7%) participants in sequence 2, 8 of 32 (25.0%) participants in sequence 3, and 6 of 31 (19.4%) participants in sequence 4.

Clinical Laboratory Safety Evaluation

All participants underwent clinical laboratory evaluations using Good Clinical Laboratory Practices (GCLP) at screening and indicated study timepoints to EOS. These included hematology, serum chemistry, and urinalysis. Overall, there were no clinically meaningful mean changes from baseline for any hematology, biochemistry, and urinalysis parameters. The TEAEs of iron deficiency anemia were reported for three (2.5%) participants for DRN, one (0.8%) participant for ACZ, and three (2.5%) participants for IHL-42X fed. TEAEs of iron deficiency were reported for one (0.8%) participant each for DRN and IHL-42X fed. There were no apparent trends in shifts from baseline for any laboratory parameters.

Plasma Pharmacokinetic Analyte Concentrations

Acetazolamide

Across all study participants, ACZ was not measurable in pre-dose samples. The mean (SD) plasma ACZ concentrations increased rapidly after the ACZ dose and peaked at the 2-h timepoint (9950 [3400] ng/mL) compared with 3.5 h (6510 [2660] ng/mL) after the IHL-42X fasted dose (Fig. 2a). After the IHL-42X fed dose, mean (SD) plasma ACZ peaked later at 6 h (6690 [2950] ng/mL) (Fig. 2b). Plasma ACZ remained measurable for all participants at the last timepoint (48 h post-dose) after each of the ACZ, IHL-42X fasted, and IHL-42X fed doses (Fig. 2).

Fig. 2.

Comparison of acetazolamide (ACZ) PK profile in comparison with the acetazolamide reference listed drug (RLD) Taro ACZ (ACZ) and IHL-42X. (a) Comparison between RLD and IHL-42X under fasted conditions; (b) comparison of IHL-42X under fasted and fed conditions

Tetrahydrocannabinol

The analyte THC was not measurable pre-dose, except for three participants, each of whom had negative pre-dose (day − 1) urine drug screens. The mean (SD) plasma THC concentrations peaked at 1 h (1.44 [1.30] ng/mL) after the DRN dose, at 1 h (1.08 [1.21] ng/mL) after the IHL-42X fasted dose (Fig. 2Fig. 3a), and at 1.5 h (2.57 [2.64] ng/mL) after the IHL-42X fed dose (Fig. 4a). Mean plasma THC levels were calculable until 6 h after the DRN and IHL-42X fasted doses (Fig. 3a), and until 12 h after the IHL-42X fed dose (Fig. 2a).

Fig. 4.

Comparison of PK profile of tetrahydrocannabinol (THC) and its metabolites for IHL-42X under fasted and fed states; (a) THC, (b) hydroxy-THC (OH-THC), and (c) carboxy-THC (COOH-THC) profiles

Fig. 3.

Comparison of PK profile of tetrahydrocannabinol (THC) and its metabolites in dronabinol reference listed drug Marinol (DRN)and IHL-42X under fasted state (a) THC, (b) hydroxy-THC (OH-THC), and (c) carboxy-THC (COOH-THC; ng/mL)

Hydroxy-THC Metabolite

The primary metabolite of THC metabolism is the psychoactive OH-THC, which is detectable in both urine and blood. This analyte was not measurable in any participants pre-dose, except for one participant in sequence 3. The mean (SD) plasma OH-THC concentrations peaked at 1.5 h (1.95 [1.36] ng/mL) after the DRN dose, at 1.5 h (1.68 [1.39] ng/mL) after the IHL-42X fasted dose (Fig. 3b), and at 2.5 h (1.73 [1.01] ng/mL) after the IHL-42X fed dose (Fig. 4b). Mean plasma COOH-THC concentrations were calculable until 16 h after each of the DRN and IHL-42X fasted doses, and until 24 h after the IHL-42X fed dose.

Carboxy-THC Metabolite

The secondary metabolite of THC metabolism is the non-psychoactive COOH-THC, which is detectable in both urine and blood as a surrogate biomarker for THC elimination. This was not measurable in any participants pre-dose, except for one participant randomized to sequence 3. The mean (SD) plasma COOH-THC concentrations peaked at 1.5 h (16.6 [8.86] ng/mL) after the DRN dose, compared with 2 h (14.9 [7.29] ng/mL) after the IHL-42X fasted dose (Fig. 3c). After the IHL-42X fed dose, the mean (SD) plasma COOH-THC peaked at 3 h (11.8 [6.37] ng/mL) (Fig. 4c). Plasma COOH-THC remained measurable for all participants at the last timepoint (48 h post-dose) after each of the DRN, IHL-42X fasted, and IHL-42X fed doses.

Analysis of Plasma Pharmacokinetic Parameters

A summary of PK parameters as described in Table 2 were deduced from the plasma concentrations of individual analytes. The PK parameters for all analytes across all treatments are presented in Table 7. Bioequivalence for ACZ, THC, OH-THC, and COOH-THC for IHL-42X relative to RLDs was concluded if the 90% CI around the geometric least squares (LS) mean ratio fell within the predefined limits (0.80 and 1.25) for the PK parameters C_max, AUC_0–last, and AUC_0–inf.

Table 7.

Summary of plasma acetazolamide, THC, OH-THC and COOH-THC pharmacokinetic parameters (pharmacokinetic parameters analysis set)

Parameter	Acetazolamide (RLD) 250 mg fasted		Dronabinol (RLD) 5 mg fasted		IHL-42X fasted		IHL-42X fed
	n	Gmean (Geo CV%)	n	Gmean (Geo CV%)	n	Gmean (Geo CV%)	n	Gmean (Geo CV%)
Analyte: Acetazolamide (ng/mL)
Cmax (ng/mL)	119	13100 (27.0)	–	–	121	7720 (38.5)	117	9620 (37.8)
Tmax (h)a	119	1.50 (0.50, 6.05)	–	–	121	3.50 (1.50, 12.0)	117	4.00 (1.03, 24.0)
AUC0–last (h × ng/mL)	119	91700 (14.6)		–	121	79900 (26.6)	117	83400 (28.5)
AUC0–inf (h × ng/mL)	119	94400 (14.9)	–	–	118	84600 (25.9)	115	86400 (28.3)
AUC%extrap (%)	119	2.51 (51.3)	–	–	118	4.18 (62.6)	115	2.93 (53.8)
AUC0–12 (h × ng/mL)	119	66400 (14.5)	–	–	121	48200 (35.5)	117	47900 (46.6)
AUC0–24 (h × ng/mL)	119	82800 (14.1)	–	–	121	67400 (29.5)	117	71700 (30.3)
T1/2 (h)	119	10.1 (16.3)	–	–	120	11.4 (24.8)	115	9.50 (15.4)
Kel (/h)	119	0.0685 (16.3)	–	–	120	0.0609 (24.8)	115	0.0730 (15.4)
CL/F (L/h)	119	2.65 (14.9)	–	–	118	2.96 (25.9)	115	2.90 (28.3)
Vz/F (L)	119	38.7 (21.7)	–	–	118	47.7 (33.8)	115	39.7 (36.2)
Analyte: THC (ng/mL)
Cmax (ng/mL)	–	–	118	1.67 (59.8)	114	1.48 (70.0)	114	3.61 (72.3)
Tmax (h)a	–	–	118	1.00 (0.50, 4.00)	114	1.00 (0.50, 6.00)	114	2.50 (1.00, 16.1)
AUC0–last (h × ng/mL)	–	–	118	2.32 (64.1)	114	2.07 (77.4)	114	9.28 (57.0)
AUC0–inf (h × ng/mL)	–	–	96	2.77 (45.7)	71	2.75 (48.7)	82	10.2 (49.4)
AUC%extrap (%)	–	–	96	8.27 (41.1)	71	8.65 (53.4)	82	3.86 (58.7)
AUC0–12 (h × ng/mL)	–	–	114	2.63 (52.8)	100	2.57 (57.3)	107	9.49 (53.7)
AUC0–24 (h × ng/mL)	–	–	114	2.66 (54.2)	99	2.59 (58.2)	103	10.2 (51.8)
T1/2 (h)	–	–	104	1.13 (40.2)	85	1.26 (55.8)	84	1.80 (66.9)
Kel (/h)	–	–	104	0.615 (40.2)	85	0.551 (55.8)	84	0.385 (66.9)
CL/F (L/h)	–	–	96	1810 (45.7)	71	1820 (48.7)	82	492 (49.4)
Vz/F (L)	–	–	96	2840 (45.7)	71	2900 (51.0)	82	1220 (57.2)
Analyte: OH-THC (ng/mL)
Cmax (ng/mL)	–	–	118	2.08 (59.3)	120	1.95 (61.2)	116	2.20 (59.3)
Tmax (h)a	–	–	118	1.50 (0.50, 4.00)	120	1.50 (0.50, 6.00)	116	2.50 (1.00, 16.1)
AUC0–last (h × ng/mL)	–	–	118	5.74 (65.4)	120	5.31 (71.3)	116	10.0 (52.6)
AUC0–inf (h × ng/mL)	–	–	110	6.73 (60.0)	97	6.54 (67.0)	105	12.0 (46.6)
AUC%extrap (%)	–	–	110	10.8 (36.3)	97	11.4 (32.9)	105	10.0 (40.3)
AUC0–12 (h × ng/mL)	–	–	117	5.80 (53.0)	119	5.29 (58.3)	116	8.60 (47.7)
AUC0–24 (h × ng/mL)	–	–	117	6.37 (57.7)	119	5.97 (62.9)	115	10.6 (44.8)
T1/2 (h)	–	–	114	3.95 (68.3)	115	4.31 (74.1)	111	6.11 (49.0)
Kel (/h)	–	–	114	0.176 (68.3)	115	0.161 (74.1)	111	0.113 (49.0)
CL/F (L/h)	–	–	110	743 (60.0)	97	765 (67.0)	105	418 (46.6)
Vz/F (L)	–	–	110	4080 (39.9)	97	4480 (35.6)	105	3620 (37.9)
Analyte: COOH-THC (ng/mL)
Cmax (ng/mL)	–	–	118	18.7 (37.2)	120	17.5 (38.5)	115	14.1 (45.6)
Tmax (h)a	–	–	118	1.50 (1.00, 4.00)	120	1.64 (1.00, 6.00)	115	3.00 (1.02, 16.1)
AUC0–last (h × ng/mL)	–	–	118	149 (54.0)	120	139 (59.4)	115	164 (50.6)
AUC0–inf (h × ng/mL)	–	–	29	204 (44.3)	29	174 (57.0)	19	233 (51.2)
AUC%extrap (%)	–	–	29	16.6 (17.2)	29	15.6 (17.0)	19	16.6 (13.8)
AUC0–12 (h × ng/mL)	–	–	118	83.7 (40.4)	120	76.8 (41.0)	115	77.7 (43.1)
AUC0–24 (h × ng/mL)	–	–	118	118 (43.0)	120	109 (44.2)	115	120 (41.0)
T1/2 (h)	–	–	85	22.0 (47.4)	84	20.1 (65.6)	74	22.9 (54.9)
Kel (/h)	–	–	85	0.0315 (47.4)	84	0.0344 (65.6)	74	0.0302 (54.9)
CL/F (L/h)	–	–	29	24.5 (44.3)	29	28.7 (57.0)	19	21.4 (51.2)
Vz/F (L)	–	–	29	577 (32.3)	29	566 (24.7)	19	485 (36.6)

PK parameters are defined in Table 2

AUC_0–last area under the drug concentration-time curve, from time zero to time of the last measurable concentration, AUC_0–inf AUC from time zero extrapolated to infinity, AUC_0–12h AUC from time zero to 12 h, AUC_0–24h AUC from time zero to 24 h, AUC_%extrap percentage of AUC that was extrapolated beyond last observed data point, C_L/F apparent total plasma clearance, COOH-THC 11-nor- Δ9-tetrahydrocannabinol-carboxylic acid, C_max maximum plasma concentration, geo CV geometric coefficient of variation, gmean geometric mean, n number of participants with observations, K_el (/h) elimination rate constant, SD standard deviation, OH-THC 11-hydroxy-Δ9-tetrahydrocannabinol, RLD reference listed drug (taro acetazolamide and marinol), t_1/2 time to reach C_max, THC Δ9-tetrahydrocannabinol, V_z/F apparent terminal volume of distribution

^aData are presented as geometric mean (geo CV%) except for T_max, which is presented as median (minimum, maximum)

For ACZ, the geometric mean (geo CV%) C_max was higher (13100 [27.0] ng/mL) after the RLD ACZ dose compared with 7720 (38.5) ng/mL after the IHL-42X fasted dose. With the IHL-42X fed dose, C_max was 9620 (37.8) ng/mL. The median T_max was 1.50 h after the ACZ dose and occurred later at 3.5 h after the IHL-42X fasted dose. With the IHL-42X fed dose, median T_max was 4.0 h. The plasma exposure to ACZ AUC parameters was slightly higher after the ACZ dose (AUC_0–last: 91700 [14.6] h × ng/mL, AUC_0–inf: 94400 [14.9] h × ng/mL) compared with the IHL-42X fasted dose (AUC_0–last: 79900 [26.6] h × ng/mL, AUC_0–inf: 84600 [25.9] h × ng/mL). With the IHL-42X fed dose, AUC_0–last was 83400 (28.5) h × ng/mL and AUC_0–inf was 86400 (28.3) h × ng/mL. The CL/F was 2.65 (14.9) L/h with ACZ, 2.96 (25.9) L/h with IHL-42X fasted, and 2.90 (28.3) L/h with IHL-42X fed. The Vz/F was 38.7 (21.7) L with ACZ, 47.7 (33.8) L with IHL-42X fasted, and 39.7 (36.2) L with IHL-42X fed. The t_1/2 was 10.1 (16.3) h with ACZ, 11.4 (24.8) h with IHL-42X fasted, and 9.5 (15.4) h with IHL-42X fed.

For THC, C_max was 1.67 (59.8) ng/mL after the RLD DRN dose compared with 1.48 (70.0) ng/mL after the IHL-42X fasted dose. With the IHL-42X fed dose, C_max was higher at 3.61 (72.3) ng/mL. The median T_max was 1.0 h with both the DRN and IHL-42X fasted doses. With the IHL-42X fed dose, median T_max was longer at 2.50 h. The plasma exposure based on the AUC_0–last and AUC_0–inf was 2.32 (64.1) h × ng/mL and 2.77 (45.7) h × ng/mL, respectively, with DRN compared with 2.07 (77.4) h × ng/mL and 2.75 (48.7) h × ng/mL with the IHL-42X fasted dose. With the IHL-42X fed dose, AUC_0–last and AUC_0–inf were higher at 9.28 (57.0) h × ng/mL and 10.2 (49.4) h × ng/mL, respectively. The CL/F was 1810 (45.7) L/h with DRN, 1820 (48.7) L/h with IHL-42X fasted, and 492 (49.4) L/h with IHL-42X fed, while the Vz/F was 2840 (45.7) L with DRN, 2900 (51.0) L with IHL-42X fasted, and 1200 (57.2) L with IHL-42X fed. The t_1/2 was 1.13 (40.2) h with DRN, 1.26 (55.8) h with IHL-42X fasted, and 1.80 (66.9) h with IHL-42X fed.

For OH-THC metabolite, the C_max was 2.08 (59.3) ng/mL after the RLD DRN dose compared with 1.95 (61.2) ng/mL after the IHL-42X fasted dose. With the IHL-42X fed dose, C_max was 2.20 (59.3) ng/mL, while the median T_max was 1.50 h with both the DRN and IHL-42X fasted doses. With IHL-42X fed, median T_max was slightly longer at 2.50 h. The plasma exposure to OH-THC based on the AUC_0–last and AUC_0-inf was similar with the DRN dose (AUC_0–last: 5.74 [65.4] h × ng/mL, AUC_0–inf: 6.73 [60.0] h × ng/mL) compared with the IHL-42X fasted dose (AUC_0–last: 5.31 [71.3] h × ng/mL, AUC_0–inf: 6.54 [67.0] h × ng/mL). With the IHL-42X fed dose, plasma OH-THC exposure was higher indicated by AUC_0–last 10.0 (52.6) h × ng/mL and AUC_0–inf 12.0 (46.6) h × ng/mL. The CL/F was 743 (60.0) L/h with the DRN dose and 765 (67.0) L/h with the IHL-42X fasted dose. The CL/F was lower at 418 (46.6) L/h with the IHL-42X fed dose. The Vz/F was 4080 (39.9) L with DRN, 4480 (35.6) L with IHL-42X fasted, and 3620 (37.9) L with IHL-42X fed, while t_1/2 was 3.95 (68.3) h with DRN, 4.31 (74.1) h with IHL-42X fasted, and 6.11 (49.0) h with IHL-42X fed.

For the COOH-THC metabolite, the C_max was similar after the RLD DRN dose (18.7 [37.2] ng/mL) compared with the IHL-42X fasted dose (17.5 [38.5] ng/mL), while the IHL-42X fed dose, the C_max was 14.1 (45.6) ng/mL. The median T_max was 1.50 h after the DRN dose and 1.64 h after the IHL-42X fasted dose, while in the IHL-42X fed dose, the T_max occurred later at 3.0 h. The exposure to COOH-THC indicted by AUC_0–last and AUC_0–inf was 149 (54.0) h × ng/mL and 204 (44.3) h × ng/mL, respectively, with DRN compared with 139 (59.4) h × ng/mL and 174 (57.0) h × ng/mL, respectively, with the IHL-42X fasted dose. With the IHL-42X fed dose, the AUC_0–last was 164 (50.6) h × ng/mL and AUC_0–inf was 233 (52.2) h × ng/mL. The CL/F was 24.5 (44.3) L/h with DRN, 28.7 (57.0) L/h with IHL-42X fasted, and 21.4 (51.2) L/h with IHL-42X fed, while the Vz/F was 577 (32.3) L with DRN, 566 (24.7) L with IHL-42X fasted, and 485 (36.6) L with IHL-42X fed. The t_1/2 was 22.0 (47.4) h with DRN, 20.1 (65.6) h with IHL-42X fasted, and 22.9 (54.9) h with IHL-42X fed.

Bioequivalence of IHL-42X Comparison to Taro Acetazolamide and Dronabinol

For ACZ, bioequivalence based on C_max was not concluded for IHL-42X fasted versus RLD ACZ (0.597 [90% CI 0.550, 0.647]), however, this was concluded for IHL-42X fasted versus ACZ based on AUC_0–inf (0.910 [90% CI 0.865, 0.958]) and AUC_0–last (0.882 [90% CI 0.838, 0.929]). In the IHL-42X fasted versus IHL-42X fed, the 90% CI were outside the predefined limits for C_max (0.807 [90% CI 0.744, 0.875]) but fell within the predefined limits for AUC_0–inf (0.993 [90% CI 0.944, 1.045]) and AUC_0–last (0.966 [90% CI 0.918, 1.017]) (Table 8). Similarly, for THC bioequivalence for IHL-42X fasted versus RLD, DRN was not concluded for C_max (0.829 [90% CI 0.705, 0.975]) or AUC_0–last (0.877 [90% CI 0.762, 1.010]) but was concluded for AUC_0–inf (0.948 [90% CI 0.822, 1.093]). For THC metabolites, OH-THC bioequivalence was concluded for IHL-42X fasted versus RLD DRN for all parameters (C_max: 0.905 [90% CI 0.801, 1.023], AUC_0–inf: 0.956 [90% CI 0.861, 1.061], and AUC_0–last: 0.919 [90% CI 0.825, 1.024]). Similarly, for the COOH-THC bioequivalence between IHL-42X fasted and RLD, DRN was concluded for C_max (0.918 [90% CI 0.838, 1.006]) and for AUC_0–last (0.946 [90% CI 0.862, 1.039]) (Table 8).

Table 8.

Statistical comparison of C_max, AUC_0–last, and AUC_0–inf between treatment groups (pharmacokinetic parameters analysis set)

	Cmax (ng/mL)			AUC0–inf (h × ng/mL)			AUC0–last (h × ng/mL)
Analyte Treatment comparison	n	Geometric LS mean ratioa	90% CIa		Geometric LS mean ratioa	90% CIa		Geometric LS mean ratioa	90% CIa
Acetazolamide
IHL-42X fasted versus RLD acetazolamide	121	0.597	(0.550, 0.647)	118	0.910	(0.865, 0.958)	121	0.882	(0.838, 0.929)
IHL-42X fasted versus IHL-42X fed	117	0.807	(0.744, 0.875)	115	0.993	(0.944, 1.045)	117	0.966	(0.918, 1.017)
THC
IHL-42X fasted versus RLD Dronabinol	114	0.829	(0.705, 0.975)	71	0.948	(0.822, 1.093)	114	0.877	(0.762, 1.010)
IHL-42X fasted versus IHL-42X fed	114	0.397	(0.345, 0.456)	82	0.262	(0.231, 0.298)	114	0.221	(0.196, 0.250)
OH-THC
IHL-42X fasted versus RLD Dronabinol	120	0.905	(0.801, 1.023)	97	0.956	(0.861, 1.061)	120	0.919	(0.825, 1.024)
IHL-42X fasted versus IHL-42X fed	116	0.880	(0.793, 0.977)	105	0.550	(0.502, 0.602)	116	0.532	(0.486, 0.584)
COOH-THC
IHL-42X fasted versus RLD Dronabinol	120	0.918	(0.838, 1.006)	29	0.779	(0.615, 0.986)	120	0.946	(0.862, 1.039)
IHL-42X fasted versus IHL-42X fed	115	1.235	(1.143, 1.335)	19	0.822	(0.641, 1.054)	115	0.850	(0.785, 0.920)

PK parameters are defined in Table 2. Bioequivalence was concluded if the 90% CIs around the ratio fell within 0.80 and 1.25

AUC_0–last area under the drug concentration-time curve, from time zero to time of the last measurable concentration, AUC_0–inf AUC from time zero extrapolated to infinity, C_max, maximum plasma concentration, CI confidence interval, LS least square, SD standard deviation, RLD reference listed drug (taro acetazolamide and marinol)

^aGeometric LS mean was obtained by exponentiating the LS mean of log-transformed PK parameters. Ratio and its 90% CI were obtained by exponentiating the LS means and CI of treatment difference

Discussion

IHL-42X is a FDC drug product in development for treatment of OSA. IHL-42X contains the Active Pharmaceutical Ingredients (APIs) DRN and ACZ, both present in marketed drugs with a long history of safe use. This phase I randomized four-period cross-over healthy volunteer (HV) PK study was conducted to assess the bioavailability, bioequivalence, and tolerability of DRN and ACZ in IHL-42X compared with their respective reference drugs, Marinol and Taro ACZ. The cross-over design included intraparticipant comparison of single-dose IHL-42X to the reference drugs and the effect of food on IHL-42X PK. Overall, 114 of 125 (91.2%) participants completed all four treatment periods. The PK data will aid in the analysis of safety and efficacy data from future clinical trials as well as establish a scientific bridge to the safety and toxicology data established for the reference listed drugs. The food effect study and data were exploratory, and aimed to characterize the impact of a high-fat meal on the IHL-42X pharmacokinetic profile, as there is known to be a substantial food effect for DRN alone. This study explores for the first time the co-formulation of acetazolamide tablets with dronabinol in sesame oil using the UniGel™ technology. Although the PK profiles were similar to those of the reference listed drugs, the differences will be taken into consideration when analyzing efficacy results from future studies in patients with OSA.

The co-formulation of ACZ and DRN into IHL-42X was based on their reported efficacies on OSA symptoms as monotherapies albeit through different drug targets and with different mechanisms of action [31, 32]. An earlier study of co-administered DRN plus ACZ as a combination for OSA demonstrated a statistically significant reduction in AHI from baseline across the three treatment doses ([low 2.5 mg DRN + 125 mg ACZ] medium 5 mg DRN + 250 mg ACZ, and high 10 mg DRN + 500 mg ACZ]) compared with placebo [29, 33]. The study reported a statistically significant improvement in Oxygen Desaturation Index (ODI), an orthogonal marker for OSA from baseline following administration of low- and medium-study-drug doses only.

Safety and Tolerability of IHL-42X

The single-dose oral IHL-42X, administered in the fasted and fed states, and the reference treatments ACZ and DRN were, overall, well tolerated in healthy adult participants. As per the previous study on the ACZ DRN combination in patients with OSA, there were some known common AEs, such as paresthesia, constipation, nausea, and diarrhea. which were observed across all doses aligning with co-administration as per prescribing information for individual monotherapies [29]. By PT, the most commonly reported TEAEs (occurring in at least 10% of participants for any treatment) with IHL-42X fasted and fed were somnolence, headache, and euphoric mood, as well as dizziness with IHL-42X fed. Although no SAEs occurred, a small proportion of participants discontinued due to TEAEs (four with IHL-42X fasted and two with IHL-42X fed), highlighting the need for continued monitoring of central nervous system (CNS)-related symptoms in subsequent trials. The intended use of IHL-42X is to treat OSA, and as such would be administered at nighttime, shortly before sleep. Somnolence may be beneficial in the intended context, as the drug would be administered at night shortly before sleep and could reduce sleep latency. Euphoric mood and dizziness may be less clinically relevant if they occur predominantly while the patient is asleep; however, these will require monitoring in patient-phase trials.

Similar commonly reported TEAEs were reported with the reference treatments, including headache with ACZ, and somnolence and euphoric mood with DRN. There did not appear to be any adverse events that were the result of the combination that were not also reported for the reference listed drugs. Overall, most participants had TEAEs that were deemed mild or moderate in severity. IHL-42X was generally well tolerated, and the safety profile of IHL-42X is similar to approved RLDs for the API components [34, 35].

Pharmacokinetic Profile of IHL-42X

The primary study objectives were to assess the bioavailability and bioequivalence of IHL-42X compared with the reference drugs under fasting conditions, and to assess the effect of food on the PK of IHL-42X in HVs. In the fasted state, exposure to each of the analytes from the IHL-42X combination product was either bioequivalent to, or lower than, exposure from the individual reference drugs. This is consistent with what is known about the metabolism of the two component APIs in IHL-42X, no impact of ACZ on the metabolism of DRN was predicted, or vice versa.

Published literature reported that ACZ is not metabolized and eliminated via the kidneys through tubular secretion and passive reabsorption following oral administration [36]. Compared with DRN that undergoes enterohepatic first pass metabolism, such phenomenon has not been reported for ACZ, precluding the potential metabolic mediated drug–drug interactions (DDI) and interference with the overall pharmacological properties of DRN, the partner drug in the IHL-42X FDC [37, 38]. THC is metabolized by cytochrome p450 enzymes, a family of enzyme that ACZ has no interaction with and as such there is no impact on drug metabolism.

There was a difference in C_max under the fasted state for THC between IHL-42X and the RLD. This is possibly due to the variability in cannabinoid bioavailability, which is known to occur even between two identical doses in the same subject [34, 39]. The difference in C_max for ACZ between IHL-42X and the RLD could be due to the slower release of ACZ from IHL-42X due to the need for the oil to dissipate from the tablet and the tablet coating to dissolve in IHL-42X compared with the RLD. The equivalence in AUC values between IHL-42X and the RLDs indicates that the total exposure to the APIs are not substantially impacted by the fixed dose combination formulation compared with the RLD formulations.

Compared with fasted conditions, administration of IHL-42X under fed conditions had a substantial impact on the bioavailability of DRN. This is consistent with the literature [40, 41] and with the DRN product information package [34]. Interestingly, in the fed state, IHL-42X demonstrated a double peak phenomenon for THC and all its metabolites (Fig. 4). This appears to be an inherent characteristic of THC in presence of food as observed in oral solution and capsule formulations other than the UniGel™ formulation [41, 42]. This could be due to variable absorption of the drug in different sections of the gut or absorption via two pathways simultaneously, lymphatic transport, enterohepatic cycle, and/or a secondary meal effect [42–45]. The increase in bioavailability of DRN in the fed versus fasted state will be critical to consider in the design of efficacy trials in patients with OSA and may also need to be considered in the development of dosing instructions.

The UniGel formulation used for IHL-42X is also used for another cannabinoid combination product under development by Incannex. IHL-675A, a combination of cannabidiol and hydroxychloroquine sulfate, has also been assessed in a phase I pharmacokinetic study [42]. The pattern of immediate release of the cannabinoid contained in the liquid contained within the soft gel cap followed by delayed release of the API contained in the solid, coated tablet is shared between the IHL-42X and IHL-675A formulations. This pattern of release is consistent with the configuration of the tablet in a gel cap formulation. The soft gel cap would dissolve, releasing the cannabinoid in oil solution. Once the oil-based cannabinoid solution had dissipated from around the tablet, the coating would be dissolved, allowing for dissolution of the API from the solid tablet.

Trial Limitations

The study was performed in healthy volunteers with a median age of 30 (range 18–65) years and only included a single dose in each treatment period, which was taken during the daytime. This demographic limitation may limit direct extrapolation of these IHL-42X PK findings to the intended OSA population that is typically older, with higher BMI and frequent metabolic comorbidities, factors known to affect the pharmacokinetics of lipophilic drugs such as dronabinol and renally cleared drugs such as acetazolamide. The statistical analysis for IHL-42X BE study was modeled off published monotherapeutic DRN and ACZ PK data to offset for the paucity of any preliminary co-formulation and/ combinational data. The observed intrasubject geometric CV for THC C_max, exceeding 59–70% (CV > 30%) across treatment arms, aligns with a classification criterion for highly variable drugs (HVDs). These findings underpin application of reference-scaled average bioequivalence (RSABE) statistical approaches in future replicate-design studies. Larger studies in patients with OSA in real-world setting, including multiple doses over a longer treatment period, would provide further insight into the performance of the drug product.

Bioequivalence was not concluded for AUC_0–inf for COOH-THC, a secondary metabolite of THC. This conclusion may have been impacted by the fact that this PK variable was estimable in only approximately 29 subjects per treatment arm, a markedly small subset of the full pharmacokinetic set.

It would also be interesting to determine the effect of concomitant medications for conditions that are frequently co-morbid with OSA, such as hypertension or diabetes, on the safety and pharmacokinetics of IHL-42X.

Conclusions

Overall, during fasting the exposure to each of the analytes from the IHL-42X combination product was either bioequivalent to, or lower than, exposure from the individual reference drugs Marinol and Taro acetazolamide. Overall, bioequivalence was demonstrated for acetazolamide (AUC_0–inf and AUC_0–last), THC (AUC_0–inf), OH-THC (all parameters), and COOH-THC (C_max and AUC_0–last). Some parameters such as ACZ (C_max) and THC (C_max, AUC_0–last) did not meet bioequivalence criteria when comparing the IHL-42X UniGel™ FDC formulation to the RLDs.

Single dose IHL-42X administered orally was, overall, well tolerated when administered in the fed and fasted states in healthy participants. Future multidose patient studies shall provide population level insights on the cumulative exposure of the IHL-42X UniGel™ product and the effect of food on the risk–benefit profile of IHL-42X in the intended patients with OSA.

Funding

This trial was funded by Incannex Healthcare, Inc. Employees of Incannex designed the study, contributed to the interpretation of the data, and wrote the manuscript. A contract research organization managed the trial on incannex’s behalf as part of ihl-42x clinical development program. the contract research Organisation conducted the data analysis. The open-access fee was paid by Incannex Healthcare, Inc.

Declarations

Conflict of Interest

GWM, AS, PA, NM, and MRB are or were employees of Incannex Healthcare Pty Ltd and have shares in the company. ER and PR have no competing interests to declare that are relevant to the content of this article.

Ethical Approval

This study was carried out according to the principles of the Declaration of Helsinki, the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) Guideline for Good Clinical Practice (GCP) E6(R2) (2016) (as adopted in Australia), and the National Health and Medical Research Council National Statement on Ethical Conduct in Human Research (2007, incorporating all updates). The study protocol was approved (approval no. 2022-12-1434 dated 3 July 2023) by Bellberry Human Research and ethics committee (123 Glen Osmond Road, Eastwood, 5063, South Australia).

Consent to Participate

Written informed consent was obtained from each subject before any trial-related procedures were performed.

Consent for Publication

Not applicable.

Code Availability

Not applicable.

Data Availability Statement

All data generated or analyzed during this study are included in this published article. The datasets generated during and/or analyzed during the current study are related to a proprietary commercial formulation and as such will not be made available.

Authors Contributions

GWM, AS, PA, NM, and MRB contributed to the study design, data collection, analysis, interpretation, and manuscript preparation. ER and PR were study principal investigators who oversaw the study implementation, data collection, analysis, interpretation, and manuscript preparation. All authors read and approved the final version and submission of this manuscript.