A pharmacokinetic/pharmacodynamic study comparing arformoterol tartrate inhalation solution and racemic formoterol dry powder inhaler in subjects with chronic obstructive pulmonary disease.

BACKGROUND: Arformoterol is a single-isomer (R,R-formoterol) nebulized long-acting beta(2)-agonist approved for use in patients with chronic obstructive pulmonary disease (COPD). Exposure (plasma concentrations of (R,R)-formoterol) and forced expiratory volume in 1s (FEV(1)) were compared for 15 microg nebulized arformoterol and 12 and 24 microg racemic formoterol (containing 6 and 12 microg (R,R)-formoterol, respectively) delivered by dry powder inhaler (DPI). METHODS: An open-label, randomized, three-way crossover study in 39 subjects with COPD (FEV(1) 1.4L, 44.4% predicted). Twice-daily treatments included nebulized arformoterol (15 microg) and racemic formoterol DPI (12 and 24 microg) for 14 days. Plasma concentrations of (R,R)- and (S,S)-formoterol were determined on days 1 and 14 of each treatment period. Airway function efficacy endpoints included the percent change in trough FEV(1) from baseline on day 14 of each treatment period. RESULTS: At steady state, exposure to (R,R)-formoterol was similar following nebulized 15 microg arformoterol (C(max): 6.5 pg/mL; AUC(0-tau): 56.5 pgh/mL) and 12 microg racemic formoterol DPI (C(max): 6.2 pg/mL; AUC((0-)(tau)()): 46.3 pgh/mL). The geometric mean ratios between these two treatments (90% confidence intervals) for C(max) and AUC((0-)(tau)()) were 0.91 (0.76, 1.09) and 1.16 (1.00, 1.35), respectively. Treatment with 24 microg racemic formoterol DPI resulted in dose proportionally higher (R,R)-formoterol: C(max) (10.8 pg/mL) and AUC((0-)(tau)()) (83.6 pgh/mL). Detectable (S,S)-formoterol was consistently measured only after treatment with racemic formoterol. The mean percent increase in trough FEV(1) was 19.1% in the arformoterol group, and 16.0% and 18.2% in the 12 and 24 microg racemic formoterol groups, respectively. Changes in (R,R)-formoterol concentrations over time paralleled changes in FEV(1). CONCLUSIONS: In this study, plasma exposure to (R,R)-formoterol was similar for nebulized 15 microg arformoterol and 12 microg racemic formoterol DPI, and 40% lower than 24 microg racemic formoterol DPI. There was no evidence of chiral interconversion following treatment with arformoterol. Finally, temporal changes in airway function in all treatment groups corresponded to changes in (R,R)-formoterol plasma concentrations.

Use of truncated areas to measure extent of drug absorption in bioequivalence studies: effects of drug absorption rate and elimination rate variability on this metric.

PURPOSE: To compare the applicability and accuracy of truncated area (AUCt; where t represents truncated time) versus area to the last quantifiable time point [AUC(O-T)] for assessing bioequivalence. Drugs with either very low or very high intra-subject variability in clearance (CL) were selected for study. Clearance variability was defined by the number of subjects with a quantifiable plasma value (Cp) at each collection time from 24 hrs to last collection time (T). METHODS: Data for amiodarone and danazol, drugs with different distributions of subject CL were examined. For amiodarone, the number of subject samples observed (test + reference) at the time of the last quantifiable concentrations was 60 at 240 hrs(T), 16 at 144 hrs and 4 at 96 hrs: while danazol had 4 at 96 hr(T), 3 at 72 hrs, 16 at 60 hrs, 7 at 48 hrs, 14 at 36 hrs, 11 at 24 hrs, 13 and 2 at 16 and 12 hrs, respectively. Simulations (Scenarios A and B) were performed to obtain populations (N = 24) with CL patterns similar to those of amiodarone and danazol. For scenario A (CL pattern similar to amiodarone), log-normally distributed CL values (28.8 L/HR) with intra-subject coefficient of variation (CV) of 25%, 40% and 60% gave the desired CL pattern. Scenario B (CL pattern similar to danazol) required that a subpopulation with an increase in CL of 40% from baseline (i.e., 40.32 L/HR) in 5%, 10% and 20% of the population represent the desired distribution. Power was evaluated by the percentage of times the simulated trials were declared bioequivalent (i.e., the number of times the test vs. reference 90% CI was within 80-125%), while accuracy was determined when the true difference in fraction absorbed (i.e., 1.25) was within the CI. Each simulation was repeated 300 times. RESULTS: The simulation results for Scenario A indicated that the statistical results using truncated area (AUCt) had power and accuracy equivalent to that obtained using the AUC(O-T) metric. However, results for Scenario B indicated that AUCt had less power and accuracy than that obtained using AUC(0-T). The confidence interval (CI) for amiodarone was the same whether AUC (0-T) or AUCt was used as the metric for extent, while for danazol, the AUC(0-T) and AUCt differed in the lower limit by 7%. CONCLUSIONS: The truncated area, AUCt, has the greatest power and accuracy when the population clearance is such that most subjects have measurable plasma concentrations at last collection time(T), resulting in a proportional loss of data from each subject.

The influence of moderate and chronic exercise training on the pharmacokinetics of procainamide and N-acetylprocainamide.

The effect of moderate and prolonged exercise on the disposition and metabolism of drugs has not been extensively examined. The present study examined the effect of exercise training on the pharmacokinetics of procainamide and its active metabolite, N-acetylprocainamide. Male Sprague Dawley rats were randomly assigned to three testing groups: (1) sedentary, (2) 4 weeks of exercise training and (3) 8 weeks of exercise training. Treadmill speed and exercise duration were gradually increased, reaching a final rate of 24 m min-1 for an hour by the end of the 4-week or 8-week period. Sedentary and exercise trained rats received a single i.p. dose of procainamide (100 mg kg-1). Serial blood samples were collected over a 10 h period and plasma samples were analysed by an UV-HPLC method. Noncompartmental analysis was performed to estimate the pharmacokinetic parameters. The t1/2 of procainamide was significantly (p < 0.05) higher in the 8 week exercise group (331 min) as compared to the sedentary group (77 min). In addition, there was a significant reduction in the amount of N-acetylprocainamide formed after 8 weeks of exercise (AUCNAPA = 739 ng mL-1 min-1). Results of this study suggest that prolonged exercise (8 weeks of training) alters the pharmacokinetics of procainamide by modifying the amount of active metabolite formed.

Application of computer-assisted radiotelemetry in the pharmacokinetic and pharmacodynamic modeling of procainamide and N-acetylprocainamide.

The cardiovascular pharmacodynamics (PD) of procainamide and N-acetylprocainamide have not been well characterized in small rodents without the presence of anesthesia or restraint. This study was undertaken to examine the pharmacokinetics (PK) and PD relationship of procainamide and N-acetylprocainamide by use of electrocardiogram (ECG) telemetry in unrestrained rats. Male Sprague Dawley rats received the following treatments: vehicle, procainamide 50 and 100 mg/kg and N-acetylprocainamide 50 and 100 mg/kg via intraperitoneal (i.p.) administration. Blood samples were collected over 8 h and subsequently analyzed. PD measurements (PQ, QS, QR, QT, RR, and HR) were collected prior to dosing and over a 24 h period. Mean PK parameters after the 50 mg/kg dose were as follows: Cls/Fprocainamide = 86.42 mL min-1 kg-1, Cls/FN-acetylprocainamide = 36.62 mL min-1 kg-1, Vdprocainamide = 10.42 L/kg, and VdN-acetylprocainamide = 5.91 L/kg. The relationship between concentration (procainamide or N-acetylprocainamide) and effect (percent change QT interval) was best described by an Emax model for procainamide (EC50 = 445 ng/mL; Emax = 30.09%). These results approximate ECG changes noted in procainamide clinical studies, suggesting that telemetry can be used as a predictive tool of efficacy. Furthermore, the proposed PK-PD model describes the electrophysiological effects associated with procainamide.

Effects of desethylamiodarone on the electrocardiogram in conscious freely moving animals: pharmacokinetic and pharmacodynamic modeling using computer-assisted radio telemetry.

Desethylamiodarone (DEA), the major active metabolite of amiodarone (AMD), plays a significant role in the electrophysiological effects observed during AMD therapy. The pharmacokinetics and pharmacodynamics of DEA were studied in rats. Animals were administered DEA (20 or 40 mg kg-1) and blood samples were collected. The heart rate, PQ, QR, QS, QT, RR intervals, and P,R,S, and T amplitudes were also measured after dosing using telemetry. DEA followed a biexponential decline with a t1/2beta of 54 center dot 8 and 46 center dot 2 h after the 20 and 40 mg kg-1 doses, respectively. The relationship between DEA and the QT interval or T amplitude was best described by a sigmoid Emax model. The mean (+/- SD) Emax for QT and T amplitude was 32 center dot 23 (+/- 2 center dot 47)% and 0 center dot 12(+/- 00 center dot 9) mV, respectively. The mean (+/- SD) EC50 value was 297 center dot 5 (+/- 22 center dot 80) ng ml-1 for QT and 139 center dot 8 (+/- 28 center dot 69) ng mL-1 for the T amplitude. The electrophysiological changes observed with DEA are similar to those with AMD. These results further support the contribution of DEA to the efficacy noted during AMD therapy and provide and viable animal for continued description of this relationship.