Comparative oral bioavailability of azimilide dihydrochloride in the fed and fasted states

Abstract

Aims

This study investigated the relative oral bioavailability of azimilide dihydrochloride following administration in the fed (high-fat meal) and fasted states.

Methods

This was a single-dose, randomized, two-way crossover study in 30 healthy, Caucasian, male subjects. Following oral administration, blood samples were collected over 27 days and analysed for azimilide using h.p.l.c. with u.v. detection. Pharmacokinetic parameters were determined using ‘noncompartmental’ analysis and compared using an anova and 90% or 95% confidence intervals.

Results

The extent of absorption was equivalent in the fed and fasted states (ratio = 96.2%; 90% CI = 90.5% −102.4%). However, C_max was decreased 19% following a high-fat meal (ratio = 81.4%; 90% CI = 76.2% −87.0%). No difference in t_max or t_½,z was observed.

Conclusions

Azimilide dihydrochloride may be orally administered to patients without regard to the prandial state.

Introduction

Azimilide dihydrochloride is a novel class III antiarrhythmic which blocks both the slowly and rapidly activating components of the delayed rectifier cardiac potassium current [1]. Clinical studies have demonstrated the drug is effective in reducing the frequency of symptomatic episodes in patients with atrial fibrillation, atrial flutter and paroxysmal supraventricular tachycardia at a maintenance dose of 100 or 125 mg day⁻¹.

Azimilide pharmacokinetics have been determined following intravenous and oral administration [2, 3]. Results from these studies indicate that azimilide is extensively metabolized with renal clearance comprising approximately 10% of total clearance. Parameters following intravenous administration includes: total clearance = 0.136 lh⁻¹ kg⁻¹; renal clearance = 0.013 lh⁻¹ kg⁻¹; steady-state volume of distribution = 12.9 l kg⁻¹; and terminal exponential half-life = 71.4 h. Following oral administration, azimilide is completely absorbed with peak concentrations occurring at approximately 6 h.

The purpose of this study was to investigate the relative bioavailability of orally administered azimilide dihydrochloride following an overnight fast and following a high fat meal.

Methods

Protocol, subjects and dosage forms

This was a single-dose, randomized, two-way crossover study in 30 healthy, drug-free, nonsmoking, Caucasian, male subjects. Subjects were institutionalized for 5 days (2 days prior to, and for 3 days after dosing). Mean (± s.d.) demographic characteristics included: age, 25.4 ± 4.81 years; height, 178.6 ± 5.72 cm; and weight (fasted dosing), 74.2 ± 3.80 kg.

All procedures were conducted in accordance with the Declaration of Helsinki and its amendments. The protocol and written consent form were approved by the Research Consultants' Review Committee, an independent review board located in Austin, TX, USA. All subjects signed informed consent forms prior to participation.

Each period lasted 27 days, and there was at least a 28 day wash-out between drug administration. Subjects were not permitted food 8 h prior to drug administration, and water (and other fluids) was withheld 4 h before dosing. Fifteen minutes prior to dosing, fed subjects began ingesting a high-fat breakfast consisting of 240 ml orange juice, one small box of cereal with whole milk, two scrambled eggs, two strips of bacon, one sweet roll, and one slice of toast with one pat of butter (fat 360 kCal; carbohydrate 284 kCal; protein 96 kCal). All subjects were administered 70 mg azimilide dihydrochloride with 180 ml tap water. A standard lunch was served at 4 h after dosing.

Venous blood samples (7 ml; sodium heparin) were collected prior to dosing and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 24, 36, 48, 72, 96, 120, 144, 192, 240, 288, 360, 432, 504, 576 and 648 h after dosing. Urine was collected before dosing and over the following intervals: 0–2, 2–4, 4–6, 6–8, 8–10, 10–12, 12–16, 16–24, 24–36, 36–48 h, and then at 24 h intervals up to 27 days. Aliquots of blood and urine were pipetted into tubes under yellow light and frozen at −20°C until assayed.

Adverse events and safety

Subjects were monitored for adverse events (AEs), abnormalities in clinical laboratory tests, vital signs, as well as with ECG and Holter monitoring throughout the study. AEs were evaluated through interviews and physical evaluations. Based on the investigator's clinical judgement, AEs were categorized as mild, moderate or severe, and causality was classified by the clinical investigator as either probably drug-related, possibly drug-related, or doubtfully drug-related.

Bioanalytical methodologies

A sensitive and specific h.p.l.c. assay with u.v. absorbance detection (340 nm) was used to determine azimilide concentrations in blood and urine [2]. Whole blood cells were lysed by successive freezing and warming. An internal standard was added to the lysed blood samples and urine samples. The samples were extracted with acetonitrile/methanol/ammonium acetate buffer, and the evaporated extract was reconstituted in mobile phase and injected into a reverse phase h.p.l.c. system. The lower limit of quantification for azimilide was 5.0 ng ml⁻¹ in blood and 50 ng ml⁻¹ in urine. The CV% for azimilide blood quality control samples was 14.9% or less over the range from 6.96 to 460 ng ml^−1. The CV% for azimilide urine quality control samples was 16.7% or less over the range of 0.12–7.08 µg ml^−1.

Pharmacokinetic and statistical methods

Pharmacokinetic parameters were determined using ‘noncompartmental’ methods [4]. These included: maximum blood concentration (C_max) and time of maximum blood concentration (t_max), determined by visual inspection; terminal exponential rate constant (λ_z), determined from log-linear least-squares regression analysis of data during the terminal exponential phase of the blood concentration-time profile; terminal exponential half-life (t_½,z), equal to ln 0.5/λ_z; area under the blood concentration-time curve (linear trapezoidal rule) to the last quantifiable blood concentration (AUC_tlast); extrapolated area under the blood concentration-time curve (AUC_ext), equal to the predicted blood concentration at the time of the last quantifiable azimilide blood concentration divided by λ_z; area under the blood concentration-time profile from 0 to infinity (AUC(0,∞)), as the sum of AUC_tlast and AUC_ext; oral clearance (CL_O), equal to Dose/AUC(0,∞); terminal volume of distribution (V_z/F), equal to CL_O divided by λ_z; and renal clearance (CL_R), equal to amount of azimilide excreted in urine from 0 to 648 h divided by area under the blood concentration-time curve from 0 to 648 h.

An analysis of variance (anova) for a two period crossover design was performed on natural logarithmic transformations of AUC(0,∞), AUC_tlast and C_max, with model terms of sequence, subject within sequence, period and treatment. The 90% confidence intervals corresponding to Schuirmann's two one-sided t-tests [5] were constructed to evaluate bioequivalence. t_max and t_½,z were assessed for normality using the Shapiro-Wilks' test, transformed if necessary and analysed using the above model with treatment comparison at the 0.05 level.

Results

Pharmacokinetics

Figure 1 illustrates mean azimilide blood concentration-time profiles following dosing in the fed (high-fat meal) and fasted states. Table 1 summarizes azimilide pharmacokinetic parameters and the statistical analysis. These results indicate that the extent of absorption is unaffected (90% CI falls within 80% to 125%) when azimilide dihydrochloride is administered after a high fat meal but that the rate of absorption is decreased. In addition, no difference is observed for t_max or t_½,z (95% CI includes 100% and 0, respectively). In addition, CL_R (0.013 l h⁻¹ kg⁻¹) comprises approximately 9% of CL_O (0.14 l h⁻¹ kg⁻¹) and V_z/F (15–18 l kg⁻¹) is consistent with wide tissue distribution.

Figure 1.

Mean azimilide blood concentration-time profiles (n = 30) following single dose oral administration of 70 mg azimilide dihydrochloride in the fed (high-fat meal, •) and fasted (□) states.

Table 1.

Bioequivalence assessment and statistical analysis of azimilide pharmacokinetic parameters in the fed (high-fat meal) and fasted states.^a

	Least square geometric means
Parameter	Fed state	Fasted stated	Point estimate of ratio: fed to fasted (%)	90% confidence interval of ratio (%)
AUCtlast (ng ml−1 h)	4825	5086	94.9	88.8, 101.3
AUC(0,∞) (ng ml−1 h)	5578	5796	96.2	90.5, 102.4
Cmax (ng ml−1)	63.7	78.3	81.4	76.2, 87.0

	Least square means
	Fed state	Fasted state	Point estimate of ratio: fed to fasted (%)	95% confidence interval: ratio of fed to fasted (%) (P value)
	Geometric means
tmax (h)	6.84	6.29	108.8	92.1, 123.2 (P = 0.1764)
	Arithmetric means		Difference of test – reference
t½,Z (h)	89.1	79.9	9.25	−0.5, 19.0 (P = 0.0626)

^aAUC_tlast = area under the blood concentration-time curve from time zero to the last quantifiable concentration; AUC(0,∞) = area under the blood concentration-time curve from time zero to infinity; C_max = maximum blood concentration; t_max = time at which the maximum blood concentration occurs; and t_½,Z = terminal exponential half-life

Adverse events and safety

A total of 47 adverse events were reported in 21 of 30 subjects. None was serious, and there were no subject withdrawals. Three subjects reported six adverse events evaluated as possibly related to study drug. These included one incidence each of headache, dizziness, euphoria, abdominal pain, diarrhoea and dyspepsia. The remaining 41 events were considered unrelated to study drug. None of the adverse events was cardiovascular in nature. No clinically significant changes in ECG, vital signs or laboratory parameters were observed.

Discussion

Azimilide pharmacokinetic parameters obtained in this study are consistent with those previously reported [2, 3]. Azimilide is a low clearance drug [3] exhibiting extensive tissue distribution and these characteristics lead to a relatively long-terminal exponential half-life, which in this study was approximately 80 h. As in previous studies [2, 3], renal clearance comprises a small percent of oral clearance (approximately 9%).

Based on the 90% confidence interval for the ratio of the azimilide AUC(0,∞) (ratio = 96.2%; 90% CI = 90.5% −102.4) the extent of azimilide absorption is equivalent in the fed (high-fat meal) and fasted states [5]. However, relative to the fasting state, C_max is decreased 19% following the high-fat meal (ratio = 81.4%; 90% CI = 76.2% −87.0%), which is not considered clinically important. Azimilide t_max and t_½,z are not significantly different between prandial states. This indicates that a high-fat meal causes an initial slowing of the absorption rate, but this does not appreciably affect the amount absorbed as illustrated in Figure 1. Based on these results, azimilide dihydrochloride may be administered without regard to timing of meals.