Cardiovascular and Pharmacokinetic Profiles of Intravenous Etripamil in Conscious Telemetered Cynomolgus Monkeys

Abstract

Paroxysmal supraventricular tachycardia (PSVT) is a common cardiac arrhythmia associated with substantial health care burden. Etripamil, a fast-acting non-dihydropyridine calcium channel blocker developed for intranasal self-administration, is currently under investigation for acute treatment of PSVT episodes. A novel two-phase study design was used to test a series of five doses of intravenous etripamil (0, 0.025, 0.05, 0.15, and 0.3 mg/kg) in conscious cynomolgus monkeys. The cardiovascular effects (e.g., blood pressure and ECG recordings) were assessed during the first phase, and the pharmacokinetic profile was characterized during the second phase. Animals were dosed remotely to avoid the stress of intranasal dosing and minimize the impact of dose administration on measurements. Results were compared with findings from subsequent intranasal studies in cynomolgus monkeys and humans. Etripamil decreased systolic blood pressure and increased heart rate proportionately in a dose-dependent manner. Etripamil also induced dose-dependent increases in the PR interval. At a dose of 0.3 mg/kg (the highest dose), the mean highest PR prolongation from baseline during 20 minutes after dosing was 27.38%. Systemic exposure to etripamil increased in a dose-dependent manner. Mean area under the curve from administration to when drug was no longer present (AUC_0–∞) values ranged from 179 to 2364 ng • min/mL, peak plasma concentration ranged from 13.2 to 176 ng/mL, and mean half-life ranged from 12.3 to 20.8 minutes (Figure 1). Results were consistent with data from subsequent intranasal preclinical and clinical studies. Intravenous etripamil demonstrated the desired targeted pharmacokinetic and pharmacodynamic profiles in conscious cynomolgus monkeys.

Introduction

Supraventricular tachycardias (SVTs) are cardiac arrhythmias originating above the bundle of His that are characterized by an elevated atrial and/or ventricular rate (>100 bpm). ¹ SVTs are associated with impaired quality of life and considerable morbidity, accounting for an estimated 50,000 emergency department visits per year in the United States (US), of which about one-fourth require hospitalization.^1,2 Paroxysmal supraventricular tachycardia (PSVT) is a subset of SVT characterized by a regular, rapid tachycardia of abrupt onset and termination, and it includes both atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT). ¹ PSVT is estimated to affect more than 2 million individuals in the US; the syndrome is seen across the lifespan and affects both men and women, however, older patients and women are at the greatest risk of developing PSVT.^1,3 Common symptoms of PSVT may include palpitations, chest discomfort, dyspnea, syncope, dizziness, and sweating, and patients may present with symptoms than range from mild to severe, or they may be asymptomatic. ⁴

Vagal maneuvers are physical techniques used to increase vagal parasympathetic tone and are considered a first-line treatment for acute termination of various SVTs including PSVT.^1,5 However, studies have shown that even when used in the appropriate patients, this intervention is effective in fewer than half of patients. ⁶ When a vagal maneuver is unsuccessful, cardioversion via intravenous administration of adenosine, a calcium channel blocker (e.g., verapamil or diltiazem), or a β-blocker may be required to restore normal sinus rhythm. ¹ There is weak evidence for the use of on demand oral antiarrhythmic treatment, also termed the “pill-in-pocket” approach, in the outpatient setting to terminate PSVT, and some guidelines have removed this as a potential treatment option.^1,7 Currently, no short-acting, noninjectable, self-administered medications are approved for immediate treatment of acute episodes of PSVT. ¹

Etripamil is a fast-acting, intranasally administered, non-dihydropyridine calcium channel blocker developed for self-administration by patients that is currently under investigation for the treatment of AV nodal–dependent PSVT episodes outside of the healthcare setting.^8,9 Intranasal administration of etripamil 70 mg results in a rapid onset of action (T_max∼7 minutes). ¹⁰ Although etripamil is associated with an approximate 2.5-hour terminal half-life (t_1/2), ¹⁰ the drug concentration declines quickly after C_max is achieved. The average concentration of etripamil falls by approximately 80% of C_max within 50 minutes of T_max, after which the slope of the elimination curve changes, resulting in the longer half-life. Etripamil is quickly metabolized by esterases in plasma to an inactive metabolite, MSP-2030, which reaches its maximum concentrations within 15 minutes after the administration of etripamil (Unpublished Data).

Attempts to accurately assess the pharmacodynamic effects of intranasal etripamil during preclinical development in conscious Cynomolgus monkeys were complicated when the animals became agitated by the experimental procedures (e.g., restraining and handling of the animals to administer drug intranasally [data on file]). Although the pharmacokinetic profile of intranasal etripamil in humans and monkeys has been characterized in earlier publications, ¹¹ the pharmacologic effects of etripamil on the cardiovascular system observed during preclinical research conducted prior to the initiation of the clinical program have not been previously described in the literature. The objective of the present study was to evaluate the pharmacodynamic effects (i.e., cardiovascular effects) and the pharmacokinetic profile of intravenous etripamil in conscious cynomolgus monkeys. To provide comparative data to support the suitability of intravenous administration as a proxy for intranasal administration, the results of two subsequent but previously unpublished pharmacokinetic studies of intranasal etripamil in conscious cynomolgus monkeys and healthy humans are also reported herein (Figure 1).

Figure 1.

Cardiovascular and pharmacokinetic profiles of intravenous and intranasal etripamil in conscious telemetered cynomolgus monkeys and healthy adult humans.

Methods

Test Substance

Etripamil (MSP-2017) was manufactured and supplied by Piramal Healthcare (Canada) Ltd. The vehicle control solution was composed of sterile water (Baxter), sodium chloride (Sigma), and sodium acetate anhydrous (Sigma), and the solution was brought to a pH of 4.5 using 1N hydrochloric acid (Fisher). Based on a 96.88% calculated purity for etripamil HCl, a correction factor of 1.03 was used. The following concentrations of dosing solutions were prepared: 0 (control), 0.015, 0.03, 0.09, and 0.18 mg/mL; concentrations were verified during the study. The pH, osmolality, and specific gravity of each dosing solution were measured during the study at first formulation occasion. Solutions were stored at 2–8°C for up to 7 days, and stability was validated during the study. Etripamil and the vehicle control solution were characterized according to the Current Good Manufacturing Practice (CGMP) Regulations of the United States Food and Drug Administration (21 CFR part 210).

Animals

Four healthy non-naïve male cynomolgus monkeys (Macaca fascicularis) and two spare monkeys age 3–5 years of Chinese origin were utilized in this study. The monkeys weighed 3.6–5.6 kg at the start of treatment.

Because all monkeys were already acclimated to the laboratory environment, they had only a 9-day waiting period before the study. Monkeys were housed in individual stainless-steel cages and kept in a controlled environment. A standard commercial diet was fed to the monkeys twice daily and water was provided ad libitum, except during designated procedures. This study was conducted in compliance with the Organization for Economic Cooperation and Development and the Good Laboratory Practice (GLP) Regulations of the United States Food and Drug Administration (21 CFR Part 58).

Study Design

This study had a two-phase design (Table 1). The cardiovascular effects (e.g., blood pressure and ECG recordings) were assessed during the first phase (treatments 1 to 5), and the pharmacokinetic profile was characterized during the second phase (treatments 6 to 10). Four male monkeys each received a series of five doses (0 [vehicle control], 0.025, 0.05, 0.15, and 0.3 mg/kg) in an escalating sequence, in each phase, for a total of 10 treatments; there was a minimum washout period of 1 day between each treatment to fully eliminate etripamil.

Table 1.

Study Design and Dosing Regimens.

Treatment	Dose Level (mg/kg)	Dose Conc. (mg/mL)	Dose Volume (mL/kg)	Dose Rate (mL/kg/hr)
1. Vehicle/Control a	0	0	1.67	50
2. Dose level 1	0.05	0.03
3. Dose level 2	0.15	0.09
4. Dose level 3	0.5	0.30
5. Dose level 4	1.0	0.60
6. Vehicle/Control a	0	0	1.67	50
7. Dose level 1	0.05	0.03
8. Dose level 2	0.15	0.09
9. Dose level 3	0.5	0.30
10. Dose level 4	1.0	0.6

^aTreatment with Vehicle/Control Item alone.

Treatment Administration

Etripamil and the vehicle control formulations were administered as a slow bolus intravenous infusion over 2 minutes, which was designed to mimic the intranasal absorption of etripamil. Doses were administered remotely via a permanent femoral intravenous catheter connected to an infusion pump by medical-grade tubing; the pump was located in the anteroom to avoid interference of the dosing activities on cardiovascular measurements and telemetry recordings, allowing the monkeys to remain calm during the treatment and monitoring periods. Doses were calculated based on the most recent body weight of each monkey. The dose rate was 50 mL/kg/hr and the dose volume was 1.67 mL/kg for all monkeys. Once an infusion period was completed, the line was flushed with saline at the same rate to ensure complete delivery of the dose, and then saline maintenance was restarted at a rate of 4 mL/hr.

Cardiovascular and Telemetry Monitoring

The telemetry transmitter (Data Science International, Model D70-PCT) was sutured in the abdominal cavity of the animals to monitor arterial blood pressure, ECG recordings, body temperature, and locomotor activity. A pressure catheter was inserted into the femoral artery, and the ECG biopotential leads were placed in a lead II configuration. The negative lead was inserted via the jugular vein and was advanced to reach above the heart, whereas the positive lead was sutured to the diaphragm at the level of the apex of the heart. Lead positioning was confirmed by waveform recognition through use of the telemetry acquisition system. The femoral vein was catheterized per standard operating procedure.

During treatments 1 to 5, at 0, 0.025, 0.05, 0.15, and 0.3 mg/kg, respectively, cardiovascular function (arterial blood pressure and ECG recordings), body temperature, and physical activity were recorded continuously for at least 60 minutes before each dosing (at approximately the same time of day for each animal and each treatment to avoid circadian-associated fluctuations) and for at least 24 hours after each dosing relative to dosing completion. The following parameters were recorded: heart rate; PR interval; PQ interval; QRS interval; QT interval; corrected QT (QTc) intervals of QTcB (Bazett’s correction), QTcF (Fridericia’s correction), and QTcV (Van de Water’s correction); systolic blood pressure (SBP); diastolic blood pressure (DBP); arterial pulse pressure; body temperature; and physical activity. However, only the endpoints most relevant to the indication or those that showed any study drug effect were reported here. Cardiovascular function parameters were reported approximately every 1 minute for 15 min pre-dose and every 1 min for the first hour following animal dosing initiation; thereafter, parameters were reported every 15 mins for 4 hours and every hour up to 24 hours post-dosing completion.

Pharmacokinetic Assessment

For treatments 6 to 10 at 0, 0.025, 0.05, 0.15, and 0.3 mg/kg, respectively, blood samples were collected from all animals at the following 15 time points: predose and 0.5, 1.5, 2.5, 3.5, 5, 10, 15, 20, 30, 45, 60, and 90 minutes; 3 hours; and 12 hours after start of dosing. Baseline was calculated as the mean of 15 pre-dose values. The animals were placed in a sling for the first 90 minutes after dose collections. Noncompartmental pharmacokinetic analysis of the plasma concentration of etripamil and MSP-2030 was performed by Pharsight Consulting Services using validated WinNonlin software. The pharmacokinetic study assessed standard parameters, peak plasma concentration (C_max), time to peak plasma concentration (T_max), area under the curve from administration to time drug is no longer detected in plasma (AUC_0–∞), λ_z (estimate of the terminal elimination rate constant), clearance, steady-state velocity, and t_1/2 when possible.

Acidified Monkey NaF / K2C2O4 Plasma samples were analyzed using LC-MS/MS (API 5000), with ACE3 column (C18, 30 × 4.6 mm, 3 μm).

Statistical Analysis

All statistics were reported using SAS (version 9.3). Statistical analyses were performed to assess the following activities and corresponding parameters: systemic blood pressure (systolic, diastolic, mean, and pulse pressure, heart rate); ECG intervals (PR, PQ, PR, QRS, QT, RR, QTcB, QTcF, QTcV); and body temperature. Other numerical data (e.g., body weight and physical activity) and nonnumerical data obtained during the conduct of the study were reported as individual results. Individual post dose measurements were adjusted for possible differences in baseline values by expressing the values as a change from predose (both absolute change and percentage change) for cardiovascular parameters. Mean and standard error were calculated for all reported numerical data.

Because the effectiveness of etripamil in terminating PSVT events appears to be directly proportional to the maximum effect on PR interval shortening and this maximum effect occurs at different times post dose for individual animals, evaluating the mean change in PR interval (vs the maximum peak effect) had the potential to underestimate the effect. To account for this, the maximum effect on PR interval in individual animals during the 20 minutes post dose was averaged to give the mean maximum effect during 20 minutes post dose, expressed as a percent change from baseline.

Because the study design corresponds to escalating doses, the dose factor was confounded with the occasion factor. The differences between etripamil and the vehicle control were assessed independently for each defined time point using a repeated measures analysis of variance with dose as the repeated factor. To express the correlations across time, the Compound Symmetry and the Heterogeneous Compound Symmetry were fitted as covariance structures in the repeated measures analysis of variance. Each pairwise comparison was conducted via a two-sided test at the 5% significance level, and significant results were reported as either P ≤ 0.001, P ≤ 0.01, or P ≤ 0.05, where P represents the considered probability.

Intranasal Studies

Brief methods for a preclinical study of intranasal etripamil in cynomolgus monkeys (MSP-2017-1212) and a phase 1 clinical study of intranasal etripamil in healthy human adults (MSP-2017-1205) are reported in the Supplement.

Results

Cardiovascular and Telemetry Monitoring

Intravenous Study

The SBP decreased in a dose-dependent manner from 0.05 to 0.3 mg/kg, starting 1 minute after dosing, except for the lowest dose (0.025 mg/kg; Figure 2A). Heart rate increased proportionately to the decreases in SBP; the rise in heart rate was also dose-dependent (Figure 2B). Peak SBP and HR values are reported in Table 2 for up to 60 min. PR intervals across dose levels are shown in Figures 3A and B, and percent change in HR and SBP following etripamil administration are depicted in Figures 3C and D.

Figure 2.

Effect of intravenous etripamil treatment on arterial blood pressure and heart rate. (A) Etripamil treatment reduced SBP in a dose-dependent manner. (B) Etripamil treatment resulted in a dose-dependent increase in heart rate proportional to the decreases in SBP. bpm: beats per minute: SBP: mean arterial blood pressure.

Table 2.

Maximum Changes in Systolic Blood Pressure and Heart Rate Across All Doses Up to 60 mins Post-Dosing.

	Systolic Blood Pressure			Heart Rate
Dose mg/kg	Baseline mmHg ± SEM	Nadir mmHg ± SEM	% Change	Baseline BPM ± SEM	Maximum Changes BPM ± SEM	% Change
0	122 ± 3.44	114.4 ± 3.86	−6.16 ± 2.47	156.1 ± 14.56	160.3 ± 10.18	3.36 ± 4.72
0.025	111.2 ± 2.76	106.4 ± 4.74	−4.27 ± 4.26	145.2 ± 11.9	175.1 ± 16.09	20.69 ± 5.45
0.05	118.8 ± 5.38	104.5 ± 2.57	−11.76 ± 2.23	150.4 ± 14.12	194.2 ± 11.19	30.54 ± 5.14
0.15	121.1 ± 1.29	94.3 ± 5.26	−22.18 ± 3.93	154.3 ± 11.84	209.4 ± 4.74	37.75 ± 9.35
0.3	119.3 ± 1.26	73.4 ± 4.15	−38.46 ± 3.35	143.4 ± 8.19	200.5 ± 6.12	40.76 ± 5.92

SEM, standard error of the mean.

Figure 3.

Effect of intravenous etripamil treatment on PR-interval, percent change in heart rate, and percent change in SBP. (A) The absolute mean of PR-interval increased after etripamil administration in a dose-dependent manner. (B) The percent change in PR-interval from baseline varied by dose level after etripamil administration. (C) Heart rate increased at all dose levels after etripamil administration and normalized by 60 min post dose. (D) SBP decreased after etripamil administration at most dose levels and SBP normalized by 60 min post dose.

Etripamil induced dose-dependent increases in the PR interval. The mean maximum effect during 20 minutes post dose was 4.53% for placebo, 6.60% at 0.025 mg/kg, 6.15% at 0.05 mg/kg, 12.13% at 0.15 mg/kg, and 27.38% at 0.3 mg/kg (Figure 4).

Figure 4.

Mean maximum percent change from baseline during 20 minutes post dose.

At the mid-high dose (0.3 mg/kg), the mean highest PR prolongation was observed 2 minutes after dosing (17.31%). The increase in PR interval 2 minutes after dosing was observed in all animals (1001, 23.89%; 1002, 31.41%; 1004, 19.47%) except 1003; however, a 22.49% PR interval increase was observed for this animal 7 minutes after dosing. At the mid-dose (0.15 mg/kg), the mean PR prolongation 2 minutes after dosing was 7.91%; the increase in PR interval 2 minutes after dosing was observed in all animals except 1004 (1001, 16.91%; 1002, 8.74%; 1003, 7.00%). A dose-dependent QTc shortening was observed at all doses and was likely due to the changes in heart rate. A review of the printed ECGs did not show any morphologic abnormalities or dysrhythmias.

Comparison with Intranasal Clinical Study

The pharmacodynamic profile of intranasal etripamil was similar to the observations in the intravenous study in monkeys. PR interval and heart rate increased in all groups compared to placebo. The rise in these parameters occurred rapidly, in less than 10 minutes. Furthermore, the pharmacodynamic changes were transient and correlated to etripamil pharmacokinetic parameters. There was no dose-response relationship in systolic blood pressure.

Pharmacokinetic Analysis

Intravenous Study

The maximum concentration of etripamil was reached immediately or shortly after the end of the 2-minute intravenous bolus infusion (Figure 5). The mean clearance values of etripamil were consistent across the dose range studied (139 to 153 mL/min/kg), and systemic exposure to etripamil increased proportionally with the dose. The mean AUC_0–∞ values of etripamil increased from 179 to 2364 ng • min/mL; C_max of etripamil increased from 13.2 to 176 ng/mL across the dose range studied. The mean half-life values of etripamil were consistent across the dose levels and ranged from 12.3 to 20.8 minutes (Table 3).

Figure 5.

Pharmacokinetic profile of etripamil administered intravenously in cynomolgus monkeys.

Table 3.

Summary PK Parameters of Etripamil in Cynomolgus Monkey Plasma.

Plasma Etripamil PK Parameters [Mean (CV%)]
Parameters	Etripamil (0.3 mg/kg)	Etripamil (0.15 mg/kg)	Etripamil (0.05 mg/kg)	Etripamil (0.025 mg/kg)
AUC0–t (ng∙min/mL)	2289 (46.5)	1070 (39.4)	349 (30.3)	149 (31.5)
AUC0–∞ (ng∙min/mL)	2364 (44.9)	1113 (38.6)	385 (26.6)	179 (26.3)
CL (mL/min/kg)	153 (52.2)	153 (41.7)	139 (33.3)	149 (31.0)
Cmax (ng/mL)	176 (104.1)	79.8 (100.9)	30.5 (58.0)	13.2 (76.9)
t1/2 (min)	20.8 (24.8)	15.3 (19.6)	12.3 (21.0)	15.3 (46.7)
tmax a (min)	3.00 (2.03, 10.00)	2.00 (2.50, 10.00)	2.50 (2.50, 3.50)	3.00 (2.50, 3.50)
Vss (mL/kg)	3681 (66.5)	3019 (55.9)	2209 (40.6)	3100 (52.8)

^aMedian (Min, Max).

Intranasal Preclinical Study (MSP-2017-1212)

Mean plasma pharmacokinetic profiles were similar on each of the pharmacokinetic measurement days for both etripamil and MSP-2030 (Days 1, 92, and 176). Measurable plasma concentrations of etripamil were observed up to 1 hour post dose for the 1.9 mg/kg/dose level (except 1 animal on day 1) and up to 1 or 4 hours post dose for the 3.8 and 5.7 mg/kg/dose levels, respectively (except for in two animals at the 5.7 mg/kg/dose), on days 1 and 92 (Figure 6).

Figure 6.

Etripamil plasma concentration following intranasal administration in cynomolgus monkeys on Day 1.

Intranasal Clinical Study (MSP-2017-1205)

Systemic exposure to etripamil following intranasal administration in humans increased in a dose-dependent manner. Across all doses investigated in the study, the peak concentrations were reached at a median time of 7 minutes. The plasma concentrations of the inactive metabolite MSP-2030 increased in a dose-proportional manner.

Comparison with Intranasal Preclinical and Clinical Studies

The pharmacokinetic profile for intranasal etripamil in humans was found to be comparable to the pharmacokinetic profile for intravenous etripamil in monkeys in this study, and to the intranasal pharmacokinetic profile in monkeys, at allometrically comparable doses (Figure 7). ¹¹

Figure 7.

Pharmacokinetic profile of intranasal delivery in humans compared with intranasal and intravenous delivery in monkeys. Pharmacokinetic profile for intranasal etripamil in humans (data not published) was comparable with the pharmacokinetic profile for intravenous etripamil in monkeys.

Discussion

Findings from this study (MSP-2017-1042) show that a slow intravenous bolus of etripamil had dose-related and reversible effects on heart rate, SBP and PR interval. The decrease in SBP was not observed in previous studies with intranasal etripamil in monkeys possibly because the excitability of the animals interfered with measurements, as described previously. Increase in heart rate and PR interval had been observed in previous intranasal etripamil studies, but it was unclear if this effect was due to behavioral effects or a true pharmacological effect of etripamil. In humans, treatment with etripamil resulted in dose-dependent decreases in SBP, which were inversely proportional to increases in heart rate. ¹⁰ In addition, etripamil induced dose-dependent increases in the PR interval.

The innovative design of remote IV dosing utilized in this study enabled more precise observations of the pharmacodynamic effects of etripamil in cynomolgus monkeys. The increase in PR interval is consistent with the expected effect of etripamil on AV nodal conduction, and the innovative design allowed for the elimination of the behavioral impact on the observations and isolate the pharmacological effect of etripamil. The therapeutic goal of etripamil is to terminate PSVT episodes through prolongation of AV nodal conduction, as reflected by an increase in the PR interval, so the objective of this study in isolating the pharmacological effect was achieved. This study may have some limitations. Using conscious telemetered cynomolgus monkeys in a controlled environment may not resemble real-world conditions that could influence pharmacokinetic and pharmacodynamic readouts.

The pharmacokinetic analysis confirmed an appropriate span of exposures generally correlated with pharmacodynamic effects. The pharmacodynamic effects observed in this study are consistent with findings in subsequent studies in humans,^8,11,12 including a phase 1 trial in healthy volunteers that showed intranasal etripamil caused PR-interval prolongation indicative of the targeted pharmacologic effect on AV nodal conduction. Furthermore, in the phase 2 NODE-1 study, intranasal etripamil rapidly terminated induced AV node–dependent SVT with a high conversion rate, ⁸ illustrating that the pharmacokinetic and pharmacodynamic properties observed in the preclinical and clinical studies presented here had the desired therapeutic effect in humans.

The pharmacokinetic and pharmacodynamic profiles observed in the current study are comparable to those observed with intranasal administration in humans, which provides valuable insights for the use of etripamil to rapidly treat patients with episodes of PSVT. Historically, noninvasive approaches for the treatment of PSVT have been limited to vagal maneuvers, per current guidelines.^1,7 However, given the low and unpredictable success rates of vagal maneuvers, a novel, noninvasive drug therapy such as intranasal etripamil, which can provide drug exposure akin to parenterally administered therapies, could emerge as a useful treatment to address the historically unmet clinical need in treating PSVT.

Conclusions

In this study, etripamil administered intravenously via remote intravenous pumps exhibited the desired targeted pharmacokinetic and pharmacodynamic profiles in conscious cynomolgus monkeys, and the results were consistent with data from subsequent preclinical and clinical studies of intranasal etripamil. These findings also confirm that the chosen study design for intravenous etripamil successfully predicted the pharmacokinetic and pharmacodynamic effects of intranasal etripamil in humans.

Appendix.

Abbreviations

AUC_0–∞

area under the curve from administration (time 0) to when drug is no longer present in plasma (∞)

ECG

electrocardiogram

SBP

systolic blood pressure

PSVT

paroxysmal supraventricular tachycardia

ORCID iDs

David B. Bharucha https://orcid.org/0009-0005-9125-3090

Douglas Wight https://orcid.org/0009-0005-3608-3228