Pharmacokinetics and safety of the nucleoside analog antiviral drug galidesivir administered to healthy adult subjects

Abstract

Galidesivir (BCX4430) is an adenosine nucleoside analog broadly active in cell culture against multiple RNA virus families, and active in animal models of viral diseases associated with Ebola, Marburg, Yellow fever, Zika, and Rift Valley fever. Current studies demonstrated the pharmacokinetics and safety of the first-in-human evaluations of galidesivir as intramuscular (IM) and intravenous (IV) formulations. Two double-blind, placebo-controlled, dose-ranging studies were conducted enrolling 126 healthy subjects. Study 1 evaluated the safety and tolerability of IM galidesivir over single day dosing, single day dosing ± lidocaine, and 7-day dosing with lidocaine. Study 2 evaluated the safety and tolerability of single ascending doses of IV galidesivir. Safety and tolerability were evaluated via clinical and laboratory monitoring. The plasma concentration-time profile of galidesivir at doses 0.3 to 10 mg/kg IM was characterized by rapid absorption, an initial rapid distribution and clearance phase, and an extended terminal elimination phase. The initial rapid distribution and extended terminal elimination were mimicked in the profile of galidesivir at doses 5 to 20 mg/kg IV. No fatal events or related serious adverse events were reported. No clinically significant dose-related trends in laboratory values, vital signs, electrocardiograms, or echocardiograms were noted. Galidesivir was safe and generally well tolerated.

Introduction

Despite advancing medical technology, existing and emerging viral diseases continue to cause tremendous morbidity and mortality worldwide. No specific antiviral therapeutics are currently available for diseases associated with many RNA viruses, such as Marburg, Yellow Fever, and Zika. A safe, stable, and effective broad-spectrum antiviral drug would have the potential to minimize the number of deaths in such viral outbreaks¹.

Galidesivir (BCX4430) is a novel nucleoside analogue that blocks viral replication by inhibiting viral RNA-dependent RNA-polymerase (RdRp) activity². Galidesivir has demonstrated antiviral activity against numerous viruses including Marburg virus (MARV), Ebola virus, MERS and SARS coronaviruses, Yellow Fever virus (YFV), Dengue virus, Japanese Encephalitis virus, West Nile virus, Rift Valley fever virus, and Tick-borne Encephalitis virus in either in vitro cell cultures or small animal models^2–6 as well as activity against both MARV and Zika virus in non-human primate animal models^2–7. Galidesivir is currently under investigation as a treatment for MARV.

Galidesivir is stable in S9 fractions across species, and in multiple cell lines and hepatocytes, is converted to the anabolite triphosphate that is the active antiviral drug species². The pharmacokinetic (PK) and safety results for 126 healthy subjects (100 subjects who received galidesivir and 26 subjects who received placebo) enrolled in the first-in-human studies of galidesivir as an intramuscular (IM) formulation (Study 1) and as an intravenous (IV) formulation (Study 2) are presented here.

Methods

The 2 studies were sponsored by BioCryst Pharmaceuticals, Inc. Both studies were conducted in compliance with the ethical principles of the Declaration for Helsinki and Good Clinical Practice Guidelines, and all subjects provided written informed consent before participation in their respective study. Study 1 assessed the PK and safety of escalating single and multiple doses of IM galidesivir. The protocol was approved by the Office for Research Ethics Committees Northern Ireland, and the study was conducted at Quotient Sciences, Nottingham, UK. Study 2 assessed the PK and safety of single doses of IV galidesivir. The protocol was approved by the Midlands Institutional Review Board, and the study was conducted at PRA Health Services, Lenexa, KS, USA. Both studies are registered in ClinicalTrials.gov (Study 1: NCT02319772; Study 2: NCT03800173).

Study Designs

Study 1.

This was a 3-part, Phase 1, double blind study in healthy subjects. In Part 1, subjects received a single-ascending dose of galidesivir or placebo (3:1 randomization) 0.3, 0.75, 1.8, 4.0, 7.0, or 10.0 mg/kg administered IM. Part 2 was an unblinded crossover evaluation where subjects received 4.0 mg/kg galidesivir + 20 mg lidocaine IM × 1 dose and one week later, 4.0 mg/kg galidesivir administered IM × 1 dose. In Part 3, subjects received 7 days of once daily dosing with galidesivir or placebo (4:1 randomization) 2.5, 5.0, or 10 mg/kg + 20 mg lidocaine administered IM. Subjects were followed for 7 days in Part 1 and 14 days in Parts 2 and 3.

Study 2.

This was a Phase 1, double blind study in healthy subjects, who received a single-ascending dose of galidesivir or placebo (3:1 randomization) 5, 10, 15, or 20 mg/kg administered IV. Subjects were followed through 21 days post-dose.

Study Assessments

In Study 1, Part 1, plasma samples were collected pre-dose, 5, 15, 30 minutes, 1, 2, 3, 4, 6, 8, 10, 12, 16, 24, 36, 48, 72, and 96 hours post-dose. In Part 2, which evaluated the effect of lidocaine on the PK of galidesivir, plasmas samples were collected on Day 1 and Day 8: pre-dose, 5, 15, 30 minutes, 1, 2, 3, 4, 6, 8, 10, 12, 16, 24, 36, 48, and 72 hours post-dose. In Part 3, after multiple ascending doses of galidesivir, plasma samples were collected on Day 1 and Day 7: pre-dose, 5, 15, 30 minutes, 1, 2, 3, 4, 6, 8, 10, 12, 16, and 24 hours post-dose. On Day 7, plasma samples were additionally collected 48, 72, and 96 hours post-dose. Urine was collected at various post-dose intervals to assess urinary excretion in Part 1 and Part 3.

In Study 2, plasma samples were collected pre-dose, halfway through the infusion (30 minutes), at the end of the infusion (1 hour), 1.25, 1.5, 2, 3, 4, 6, 8, 10, 12, 16, 24, 36, 48, 60, 72, 96, 120, 168, 312, and 480 hours post-infusion. Urine was collected at various post-dose intervals to assess urinary excretion.

In both studies, safety assessments included blood and urine laboratory analyses, electrocardiograms (ECGs: 12 lead and telemetry), echocardiograms (ECHOs), vital signs, and physical examination. Study 1 also included the assessment of injection site reactions for the IM administration of galidesivir. Adverse events were assessed (graded) for severity and classified using the study-specific modified 2014 Division of Microbiology and Infectious Diseases (DMID) Adult Toxicity Grading Scale.

Bioanalytical Methods

Plasma and urine samples were analyzed using validated HPLC/MS/MS methods. For Study 101, the plasma assay range was 5.0 to 3500 ng/mL with a sample volume of 100 μL, and for Study 102, the plasma assay range was 20 to 10000 ng/mL with a sample volume of 25 μL. The urine dynamic range for Study 1 was 5 to 3500 ng/mL and 50 to 25000 ng/mL for Study 2. Deuterated galidesivir was used as internal standard. Analytical methods for urine and plasma for both studies used an Acquity BEH Amide HPLC column, and samples were extracted with 5 volumes of acetonitrile/water. The mobile phase was a gradient of 50 mM ammonium formate and acetonitrile. MS/MS detection settings were 266.1 ->207 for galidesivir and 269.1->210 for the internal standard. Interassay variability was less than 10% over the range of each assay.

Data Analysis

In both studies, the sample size was based on experience in other single- and multiple-ascending dose studies. A sample size of 6 subjects/cohort receiving single doses of galidesivir and 8 subjects/cohort receiving multiple doses of galidesivir was deemed adequate to assess the PK and safety in both Study 1 and Study 2. In Study 1, Part 2, the sample size of 14 subjects was based on number of subjects anticipated to be needed to assess a comparative bioavailability of galidesivir + lidocaine in comparison to galidesivir alone.

Plasma concentration time data in Study 1 and Study 2 were analyzed using noncompartmental methods in Phoenix WinNonlin (Certara USA, Inc, Princeton, NJ). In Study 1, galidesivir PK parameters that were estimated included maximum concentration (C_max), last measurable concentration of drug (C_last), time to maximum concentration (T_max), area under the concentration time curve (AUC) from time 0 to last time (AUC_0-last), AUC from time 0 to infinity (AUC_0-inf), apparent clearance after IM administration (CL/F), apparent volume of distribution after IM administration (Vz/F), percentage of AUC extrapolated between AUC_0-last and AUC_0-inf (AUC_extrap), λz, AUC_tau (AUC over the dosing interval, tau; Part 3 only), and half-life (t_1/2). PK parameters for galidesivir were estimated where possible for each subject for Day 1 (all Parts), Day 8 (Part 2) and Day 7 (Part 3 only) for all active dose levels unless otherwise specified. In Part 2, administration of galidesivir alone was considered “reference” and administration of galidesivir + lidocaine was considered “test”. Geometric least squares mean (GLSM) ratios and 90% confidence interval (CI) constructed from a mixed-effect model with sequence, period, and treatment as fixed effects and subject-within-sequence as a random effect was used to assess the effect of lidocaine on the galidesivir C_max, AUC_0-last, and AUC_0-inf. A 90% CI around the GLSM ratio of 80.0 to 125.0 % of test versus reference was used to indicate whether there was an effect of lidocaine on galidesivir PK. In Study 2, galidesivir PK parameters that were estimated included C_max, C_last, T_max, AUC_0-last, AUC_0-inf, clearance (CL), volume of distribution (V_z), AUC_extrap, λ_z, and t_1/2.

Dose proportionality in Study 1 and Study 2 for AUC_0-inf, AUC_0-t (or AUC_tau, where appropriate), and C_max was evaluated using the power model (including all doses) and also using an analysis of variance (ANOVA) model where each dose was compared with a reference dose on a pairwise basis.

For urine excretion assessments in Study 1 and Study 2, A_e, %dose_excreted, and CL_R were calculated.

Results

Baseline Patient Characteristics

In Study 1, 48 subjects were enrolled and randomized in the single-ascending dose part (36 to galidesivir and 12 to placebo), 17 subjects were enrolled in the lidocaine part, and 29 subjects were enrolled and randomized in the multiple-ascending dose part (23 to galidesivir and 6 to placebo). In Study 2, 32 subjects were enrolled and randomized (24 to galidesivir and 8 to placebo). All subjects were dosed with study drug.

The demographic characteristics were generally balanced across both studies (Table 1). Median age ranged from 26.0 to 36.5 years across galidesivir- and placebo-treated subjects. Most subjects were white/Caucasian and male. Five of the 126 enrolled subjects discontinued study participation early: 3 and 1 in the lidocaine and multiple-ascending dose parts of Study 1, respectively, and 1 in Study 2 (Supplementary Figure S1).

Table 1. Demographic and baseline characteristics.

BMI, body mass index; IM, intramuscular; IV, intravenous; MAD, multiple ascending dose; SAD, single ascending dose

Demographics	Study 1 (IM)					Study 2 (IV)
	Part 1: SAD		Part 2: Lidocaine	Part 3: MAD		SAD
	Galidesivir N = 36	Placebo N = 12	Galidesivir N = 17	Galidesivir N = 23	Placebo N = 6	Galidesivir N = 24	Placebo N = 8
Median age (range), years	26.0 (19, 48)	27.0 (21, 38)	26.0 (19, 49)	33.0 (19, 49)	32.0 (19, 46)	35.5 (21, 54)	29 (25, 45)
Male, n (%)	25 (69.4)	9 (75.0)	14 (82.4)	19 (82.6)	3 (50.0)	16 (66.7)	3 (37.5)
Race, n (%)
White	32 (88.9)	11 (91.7)	14 (82.4)	17 (73.9)	5 (83.3)	17 (70.8)	2 (25.0)
Black	2 (5.6)	1 (8.3)	2 (11.8)	2 (8.7)	1 (16.7)	7 (29.2)	5 (62.5)
Asian	2 (5.6)	0	0	3 (13.0)	0	0	0
Other	0	0	1 (5.9)	1 (4.3)	0	0	1 (12.5)
Median BMI (range), kg/m2	24.70 (20.1, 32.1)	25.70 (19.9, 31.2)	26.20 (21.4, 30.9)	25.30 (21.8, 30.3)	27.55 (24.3, 29.1)	24.55 (20.4, 30.4)	25.60 (20.7, 27.6)

Pharmacokinetic Analysis

The plasma concentration-time profile of galidesivir at doses 0.3 to 10 mg/kg administered intramuscularly was characterized by rapid absorption, an initial rapid distribution and clearance phase, and an extended terminal elimination phase (Figure 1A). The initial rapid distribution followed by the extended terminal elimination phase was mimicked in the plasma concentration-time profile at galidesivir doses 5 to 20 mg/kg administered intravenously as a 60-minute infusion (Figure 1B).

Figure 1. Plasma galidesivir concentration-time profiles (mean ± SD).

A) After single, ascending, intramuscular doses of galidesivir (study 1, part 1), B) After single, ascending, intravenous, 60-minute infusions of galidesivir (study 2)

Galidesivir pharmacokinetic characteristics following single, ascending intramuscular and intravenous administrations

The PK parameters following single IM and IV administrations of galidesivir are provided in Table 2 and Table 3. Maximum galidesivir concentrations were observed approximately 15 minutes after the IM injections. Following IV galidesivir doses, the mean elimination t_½ ranged from 104 to 175 hours; in Study 1, PK samples were not collected for a sufficient duration to accurately reflect the half-life of galidesivir. The arithmetic mean (standard deviation, SD) cumulative percent of galidesivir excreted in urine over the 48-hour collection period following IM administration ranged from 25.2% (8.4%) to 34.7% (32.9%) and over the 96-hour collection period following IV administration, the arithmetic mean (SD) cumulative percent of galidesivir dose excreted ranged from 33.3% (17.0%) to 46.3% (4.8%). Bioavailability (%F) of the IM formulation was approximately 84% based on the 10 mg/kg dose of galidesivir.

Table 2. Pharmacokinetic parameters following single intramuscular doses of galidesivir.

In Study 1, healthy subjects received single intramuscular doses of galidesivir (n=6/dose). Doses were administered as 1‑4 intramuscular injections. Fourteen subjects received galidesivir alone and co-administered with 20 mg of lidocaine, separated by a week.

Dose mg/kg	Cmax, ng/mL Mean (SD)	Tmax, h Median (range)	AUC0-t, ng.h/mL Mean (SD)	% Dose excreted in urine Mean (SD)
Single dose, intramuscular administrations of galidesivir (Study 1, Part 1)
0.3	167 (30.5)	0.75 (0.25, 1.05)	518 (18.6)	27.7 (2.6)*
0.75	562 (37.0)	0.25 (0.25, 0.50)	1340 (7.0)	27.8 (7.1)
1.8	1000 (28.6)	0.25 (0.08, 0.25)	3890 (8.0)	31.2 (5.9)
4.0	2760 (31.2)	0.25 (0.25, 0.50)	10100 (12.1)	33.0 (32.9)
7.0	5760 (25.7)	0.25 (0.25, 0.25)	18900 (12.0)	34.7 (5.4)
10	7980 (30.6)	0.375 (0.25, 0.50)	27100 (17.7)	25.2 (8.4)
Single dose, intramuscular administration of galidesivir with and without lidocaine (Study 1, Part 2)
4	2930 (33.7)	0.25 (0.25, 0.50)	10200 (12.3)	N/C**
4 + lidocaine	3000 (22.7)	0.25 (0.08, 0.50)	10400 (11.1)	N/C**

^*Following administration of 0.3 mg/kg, the amount excreted in urine was calculated through 48 hours. For all other doses, the amount excreted was calculated through 96 hours.

^**Urine was not collected in Part 2

Table 3. Pharmacokinetic parameters following single intravenous doses of galidesivir.

In Study 2, healthy subjects received single, 60‑minute, intravenous infusions of galidesivir (n=6/dose).

Dose mg/kg	Cmax, ng/mL Mean (SD)	Tmax, h Median (range)	AUC0-t, ng.h/mL* Mean (SD)	t1/2 (h) Mean (SD)	CL (L/h) Mean (SD)	Vz (L) Mean (SD)	Clr (L/h) Mean (SD)	% Dose excreted in urine Mean (SD)
Single dose, 60-minute intravenous infusions of galidesivir (Study 2)
5	5560 (425)	1.00 (1.00, 1.00)	17840 (4116)	116.3 (45.6)	17.4 (3.4)	2775 (611)	9.4 (1.6)	27.7 (2.6)**
10	10500 (2250)	1.00 (0.50, 1.02)	32730 (5103)	103.9 (21.0)	20.9 (2.5)	3107 (678)	11.8 (2.2)	27.8 (7.1)
15	17950 (2942)	1.00 (1.00, 1.03)	60730 (12569)	174.8 (36.3)	16.8 (2.2)	4198 (797)	11.6 (1.6)	31.2 (5.9)
20	20720 (3389)	1.00 (1.00, 1.02)	73940 (10540)	161.5 (54.0)	18.1 (2.5)	4083 (873)	8.6 (4.7)	33.0 (32.9)

^*AUC0-t for Study 2: Following administration of the 5 and 10 mg/kg dose, AUC0-t was measured through 168 hours, for 15 mg/kg dose, AUC0-t was measured through 480 hours and for 20 mg/kg dose, AUC0-t was measured through 312 hours.

From the dose proportionality analysis based on the power model (slope [90% CI]), galidesivir AUC_0-t (1.15 [1.12, 1.18]) and C_max (1.09 [1.02, 1.16]) increased in a slightly more than dose-proportional manner over the entire single IM dose range of 0.3 mg/kg to 10.0 mg/kg; moreover, upon closer evaluation using an ANOVA, a lower than dose proportional increase was observed at the lower doses and a higher than dose proportional increase was observed at the higher doses for AUC_0-t, and C_max.

However, evaluating data from the IV administrations, the dose proportionality analysis also based on the power model (slope [90% CI]), galidesivir AUC_0-inf (1.00 [0.87, 1.23]), AUC_0-t (1.09 [0.95, 1.22]), and C_max (0.98 [0.87, 1.10]) increased in a dose-proportional manner over the single dose range of 5.0 to 20.0 mg/kg.

Evaluation of coadministration of lidocaine with galidesivir

The ratio of GLSM from the ANOVA model for galidesivir + lidocaine/galidesivir and the 90% CIs for C_max and AUC_0-inf were 102.65% (92.13, 114.38) and 102.13% (98.93, 105.43), respectively. Given the 90% CIs for both exposure parameters fell between 80% and 125%, it was determined that co-administration of IM lidocaine in the same injection did not affect the PK parameters of IM galidesivir.

Galidesivir pharmacokinetic characteristics following seven days of daily, intramuscular administrations

The galidesivir plasma concentration-time profile from Day 7 (Figure 2B) followed a similar contour as seen on Day 1 (Figure 2A).

Figure 2. Plasma galidesivir concentration-time profiles (mean ± SD).

A) From Day 1 of the 7-day, intramuscular, ascending dose regimen (study 1, part 3), B) From Day 7 of the 7-day, intramuscular, ascending dose regimen (study 1, part 3)

Galidesivir pharmacokinetic characteristics following multiple ascending doses of intramuscular administration

The PK parameters following 7 days of IM administration of galidesivir are provided in Table 4. As observed with single ascending IM administrations of galidesivir, the T_max following 7 days of dosing was typically achieved in 15 minutes. The estimated mean Day 7 t_½ for galidesivir was approximately 87 to 116 hours. The mean CL_R ranged from 7.9 to 12.1 L/h on Day 7, with similar results following single IV administration.

Table 4. Pharmacokinetic parameters of galidesivir following multiple dose intramuscular administration of galidesivir.

In Study 1, Part 3, healthy subjects received galidesivir and 20 mg of lidocaine, once daily, intramuscularly over 7 days. Doses were administered as 1‑4 intramuscular injections. Data presented as Mean (SD) except for T_max which is presented as Median (range).

Pharmacokinetic Parameter, units	Galidesivir Dose
	2.5 mg/kg (N = 7)		5.0 mg/kg (N = 8)		10.0 mg/kg (N = 8)
	Day 1	Day 7	Day 1	Day 7	Day 1	Day 7
Cmax, ng/mL	1850 (311)	2540 (987)	6890 (841)	6990 (1170)	11700 (2880)	23300 (24300)
Tmax, h	0.25 (0.08, 0.50)	0.25 (0.10, 0.52)	0.25 (0.25, 0.50)	0.25 (0.08, 0.25)	0.25 (0.25,0.25)	0.25 (0.08,0.50)
Ctau, ng/ mL	34.5 (8.6)	140 (26.4)	69.1 (10.8)	284 (54.4)	136 (20.2)	500 (82.5)
AUC0-t, ng.h/mL	4890 (817)	N/A	12200 (1430)	N/A	21700 (2180)	N/A
AUCtau,ng.h/mL	N/A	7720 (1280)	N/A	17700 (1760)	N/A	34700 (449)
t1/2, h	NC	105 (17.1)	NC	86.8 (14.6)	NC	116 (29.3)
CL/Fss, L/h	N/A	25.1 (2.5)	N/A	22.4 (2.1)	N/A	22.6 (4.4)
Vz/Fss, L	N/A	3800 (23.5)	N/A	2820 (696)	N/A	3740 (972)
CLR, L/h	N/A	12.1 (1.4)	N/A	7.9 (1.4)	N/A	9.5 (1.7)
Rac, Cmax	N/A	1.37 (0.45)	N/A	1.0 (0.20)	N/A	2.0 (2.1)
Rac, AUC	N/A	1.58 (0.14)	N/A	1.45 (0.06)	N/A	1.6 (0.16)
% excreted in urine	25.3 (10.5)	48.2 (5.2)	21.4 (7.3)	35.8 (7.9)	29.4 (7.6)	42.6 (6.1)

Assessment of trough concentrations of galidesivir suggested that steady state had not been achieved by Day 7 and that further accumulation would be expected to occur should dosing extend beyond 7 days.

Results from the power model indicated that over the dose range of 2.5 to 10.0 mg/kg, the slope (90% CI) for AUC_tau was consistent with dose proportionality on Day 1 (1.09 [0.98, 1.19]) and Day 7 (1.09 [1.00, 1.18]); C_max showed a modestly greater than dose-proportional increase over the same dose range on Day 1 (1.32 [1.13, 1.51]) and Day 7 (1.44 [1.13, 1.74]).

Dose proportionality was observed from the ANOVA results for AUC_tau from 5.0 to 10.0 mg/kg, though this was more evident on Day 7, with a GLSM (90% CI) ratio of test (10 mg/kg) to reference (5.0 mg/kg) of 0.98 (0.87, 1.11). Near dose proportionality was also observed for AUC_tau from 2.5 to 5.0 mg/kg on Day 7 with a GLSM (90% CI) ratio of test (2.5 mg/kg) to reference (5.0 mg/kg) of 0.87 (0.77, 0.98). The 90% CIs for GLSM comparisons of C_max including unity, consistent with dose proportionality for C_max across this range (Day 7, test [2.5 mg/kg] to reference [5.0 mg/kg]: [0.45, 1.05] and test [10 mg/kg] to reference [5.0 mg/kg]: [0.83, 1.93]).

The ratio of GLSM from the ANOVA model for AUC_tau/AUC_0-t was used to evaluate dose accumulation. Overall, there was an approximately 1.5-fold increase in exposure (AUC) with repeat dosing of galidesivir over 7 days. This degree of accumulation (ratio) was consistent across the 3 dose cohorts studied: 2.5 mg/kg (1.58), 5.0 mg/kg (1.45), and 10 mg/kg (1.58).

Safety Analysis

No fatal adverse events or study drug-related serious adverse events (SAE) were reported in either study. There were no study drug-related treatment-emergent adverse events (TEAE) that led to discontinuation from the study (Supplementary Table S1). No clinically significant dose-related trends were observed in blood and urine laboratory values, vital signs, physical examinations, ECGs, or ECHOs.

All subjects in Study 1 Part 1 completed the study; 3 subjects in Part 2 withdrew from the study after one period because of investigational medicinal product issues (temperature excursion). Study drug was withdrawn from a subject in Part 3 (10 mg/kg galidesivir + 20 mg lidocaine) on Day 4 of treatment after the subject experienced nausea, vomiting, and abdominal pain, which the investigator assessed as the symptoms of anticipatory anxiety around the receipt of study drug injections. In Study 2, 1 subject was lost to follow-up after infusion of the study drug.

There were two unrelated serious adverse events reported in Study 2. One subject became pregnant while enrolled in Study 2, and the pregnancy ended with an early gestational spontaneous abortion. This event was considered related to the subject’s pre-existing risk factors of advanced maternal age (40 years), history of a prior spontaneous abortion, and obesity (BMI, 30.4 kg/m²). Another Study 2 subject was found to have a previously undiagnosed advanced gastroesophageal cancer via computed tomography (CT) imaging when he presented to the hospital for evaluation of abdominal pain. Neither event was considered related to galidesivir.

The most frequently reported TEAE across both studies was headache (Supplementary Table S2). In Study 1, 3 of 18 subjects (17%) who received placebo experienced a TEAE of headache, while 11 of 76 subjects (14%) who received galidesivir experienced a TEAE of headache, and 3 of the events were assessed as possibly drug-related by a blinded investigator. In Study 2, none of 8 subjects (0%) who received placebo experienced a TEAE of headache. Among the 32 subjects in Study 2 who received galidesivir, 3 subjects (9%) experienced a TEAE of headache, and all 3 events were assessed as possibly drug-related by a blinded investigator. An alternate etiology provided by the investigator for at least 1 headache event assessed as drug-related was caffeine withdrawal, which is a recognized common phenomenon among research subjects in Phase 1 clinical research units^8–11. Across both studies, there was no apparent dose-response relationship between galidesivir and headache events, and the incidence of headache events was not significantly different between subjects treated with placebo and those treated with galidesivir (Supplementary Table S2).

In addition, injection site pain was reported in 28 subjects who had received the IM formulation of galidesivir (Supplementary Table S2). The IM injection site pain was not found to be galidesivir dose- or injection site-dependent. The incidence of IM injection site pain was greatly reduced by the co-administration of lidocaine with galidesivir in Study 1, Part 2, which subsequently led to the use of lidocaine with all IM doses in Study 1, Part 3.

In summary, galidesivir was found to be safe and generally well tolerated following single and repeat dosing in healthy subjects, and no safety signals were identified.

Discussion

In these 2 first-in-human studies, the PK of both IM and IV administered galidesivir was examined. Study 1 was a 3-part dose-ranging study of galidesivir administered by IM injection, and Study 2 was a single ascending dose dose-ranging study of galidesivir administered by IV infusion. PK was characterized and dose proportionality was evaluated (power model and ANOVA) following single (Study 1, Part 1) and multiple (Study 1, Part 3) ascending IM doses of galidesivir, and following single (Study 2) ascending IV doses of galidesivir administered as a 60 minute infusion. The effect of co-administered lidocaine on the PK of IM galidesivir was also evaluated (Study 1, Part 2).

The 10 mg/kg dose was the only single dose administration of galidesivir in common between the 2 two studies. Exposure parameters were modestly higher for 10 mg/kg IV vs. IM, with %F of 84%. In Study 1, the sampling duration was insufficient to accurately measure half-life of galidesivir. In Study 2, PK samples were collected for up to 480 h after dosing in order to provide a better estimate of half-life (median of 114.5 h). The AUC_0–96 (SD) was the same for both routes of administration, 27400 h.ng/mL (3645) for IV vs. 27400 h.ng/mL for IM (4770).

The plasma PK concentration-time profile of galidesivir at all doses (both IM and IV) was characterized by an initial rapid distribution followed by an extended terminal elimination phase with a very long plasma half-life. Following single ascending doses, galidesivir AUC and C_max increased in a dose proportional manner over the range of 5 to 20 mg/kg. With multiple doses, the long half-life of galidesivir resulted in accumulation ratios of approximately 1.5-fold for C_max and AUC. However, steady state was apparently not achieved by the 7^th day of dosing, and further accumulation would be expected to occur if dosing extended beyond 7 days. As it would be advantageous to achieve optimal drug levels as quickly as possible in the treatment of serious or life-threatening viral infections, a loading dose/maintenance dose strategy might safely achieve steady state C_tau after the first dose. Loading dose/maintenance dose regimens will be tested in future studies.

The IM formulation of galidesivir used in Study 1 has a solubility limit of 100 mg/mL in sterile solution. At galidesivir doses of ≥ 4 mg/kg, multiple IM injections (up to 4 injections for a 10 mg/kg dose) were required to deliver each dose across multiple large muscle groups (e.g., ventrogluteal, dorsogluteal, vastus lateralis). IM injection of galidesivir was associated with significant injection site pain, but the pain was greatly ameliorated by co-administration of 20 mg of lidocaine. The inclusion of lidocaine in the galidesivir injection had no effect on the PK of galidesivir. However, given the practical limitations of IM administration, especially the numerous injections that would be required for a loading dose/maintenance dose regimen with multiple day dosing, IV appears to be the preferable parenteral route of galidesivir administration.

In these 2 first-in-human studies, the safety of both IM and IV administered galidesivir was thoroughly examined with blood and urine laboratories, vital signs, physical examinations, ECGs, ECHOs, and adverse event reporting. No toxicities were identified for any galidesivir dose level, and the only adverse drug reaction identified as clearly related was injection site pain, and only when galidesivir was administered by IM injection without co-administration of lidocaine. In contrast, galidesivir IV administration was well tolerated, and the IV formulation and route of administration will be used in subsequent studies. Given the high doses administered and plasma exposures achieved in the 100 galidesivir-treated subjects, it is notable that no safety concerns were identified for galidesivir in these 2 studies.

Conclusion

Galidesivir, a broad-spectrum adenosine nucleoside analog viral RdRp inhibitor, is a safe and tolerable antiviral drug with a favorable PK profile. The findings from this study support further clinical development of the IV formulation of galidesivir as a treatment for RNA viruses.