Effects of CYP3A4 inhibition and induction on the pharmacokinetics and pharmacodynamics of tolvaptan, a non-peptide AVP antagonist in healthy subjects

AIMS

In vitro studies indicated CYP3A4 alone was responsible for tolvaptan metabolism. To determine the effect of a CYP3A4 inhibitor (ketoconazole) and a CYP3A4 inducer (rifampicin) on tolvaptan pharmacokinetics (PK) and pharmacodynamics (PD), two clinical trials were performed.

METHODS

For CYP3A4 inhibition, a double-blind, randomized (5:1), placebo-controlled trial was conducted in 24 healthy subjects given either a single 30 mg dose of tolvaptan (n = 19) or matching placebo (n = 5) on day 1 with a 72 h washout followed by a 3 day regimen of 200 mg ketoconazole, once daily with 30 mg tolvaptan or placebo also given on day 5. For CYP3A4 induction, 14 healthy subjects were given a single dose of 240 mg tolvaptan with 48 h washout followed by a 7 day regimen of 600 mg rifampicin, once daily, with 240 mg tolvaptan also given on the seventh day.

RESULTS

When co-administered with ketoconazole, mean C_max and AUC(0,∞) of tolvaptan were increased 3.48- and 5.40-fold, respectively. Twenty-four hour urine volume increased from 5.9 to 7.7 l. Erythromycin breath testing showed no difference following a single dose of tolvaptan. With rifampicin, tolvaptan mean C_max and AUC were reduced to 0.13- and 0.17-fold of tolvaptan administered alone. Twenty-four hour urine volume decreased from 12.3 to 8.8 l.

CONCLUSIONS

Tolvaptan is a sensitive CYP3A4 substrate with no inhibitory activity. Due to the saturable nature of tolvaptan''s effect on urine excretion rate, changes in the pharmacokinetic profile of tolvaptan do not produce proportional changes in urine output.     

Pharmacokinetics of teduglutide in subjects with renal impairment

Purpose

Teduglutide is a recombinant analogue of human glucagon-like peptide-2 that has recently been approved for the treatment of short bowel syndrome in adults. This study was designed to study the influence of renal function and age on teduglutide pharmacokinetics.

Methods

This was an open-label study with six parallel groups (6 subjects each). Three groups with renal impairment (moderate, severe and end-stage renal disease) were compared to healthy subjects with normal renal function, which were matched to the renal-impaired subjects with respect to demographics. At least two elderly subjects (≥65 years) were enrolled per group. A single dose of 10 mg teduglutide was subcutaneously administered to each subject. Teduglutide plasma concentrations were measured using a validated liquid chromatography method with tandem mass spectrometric detection, and the primary pharmacokinetic variables (AUC_inf and C_max) were calculated.

Results

Area under the concentration versus time curve extrapolated to infinity (AUC_inf) and maximum plasma concentration (C_max) of teduglutide in subjects with end-stage renal disease were approximately 2.59- and 2.08-fold higher, respectively, than those of healthy subjects. The AUC_inf and C_max were also slightly higher in subjects with moderate and severe renal impairment. Comparison of healthy subjects aged <65 years with healthy elderly subjects revealed very similar pharmacokinetics in both subgroups.

Conclusions

In our study population, the primary pharmacokinetic parameters of teduglutide increased with increased severity of renal impairment. These results suggest that the daily dose of teduglutide should be reduced by 50 % in patients with moderate and severe renal impairment and end-stage disease. We found no effect of age on the pharmacokinetics of teduglutide in healthy subjects. The treatment was well tolerated, and there were no safety concerns.     

Bayesian Approach to Estimate AUC,Partition Coefficient and Drug Targeting Index for Studies with Serial Sacrifice Design

Purpose

The current study presents a Bayesian approach to non-compartmental analysis (NCA), which provides the accurate and precise estimate of AUC ₀ ^∞ and any AUC ₀ ^∞ -based NCA parameter or derivation.

Methods

In order to assess the performance of the proposed method, 1,000 simulated datasets were generated in different scenarios. A Bayesian method was used to estimate the tissue and plasma AUC ₀ ^∞ s and the tissue-to-plasma AUC ₀ ^∞ ratio. The posterior medians and the coverage of 95% credible intervals for the true parameter values were examined. The method was applied to laboratory data from a mice brain distribution study with serial sacrifice design for illustration.

Results

Bayesian NCA approach is accurate and precise in point estimation of the AUC ₀ ^∞ and the partition coefficient under a serial sacrifice design. It also provides a consistently good variance estimate, even considering the variability of the data and the physiological structure of the pharmacokinetic model. The application in the case study obtained a physiologically reasonable posterior distribution of AUC, with a posterior median close to the value estimated by classic Bailer-type methods.

Conclusions

This Bayesian NCA approach for sparse data analysis provides statistical inference on the variability of AUC ₀ ^∞ -based parameters such as partition coefficient and drug targeting index, so that the comparison of these parameters following destructive sampling becomes statistically feasible.     

Effect of Activated Charcoal on Apixaban Pharmacokinetics in Healthy Subjects

Background

Activated charcoal is commonly used to manage overdose or accidental ingestion of medicines. This study evaluated the effect of activated charcoal on apixaban exposure in human subjects.

Methods

This was an open-label, three-treatment, three-period, randomized, crossover study of single-dose apixaban (20 mg) administered alone and with activated charcoal given at 2 or 6 h post-dose to healthy subjects. Blood samples for assay of plasma apixaban concentration were collected up to 72 h post-dose. Pharmacokinetic parameters, including peak plasma concentration (C _max), time to C _max (T _max), area under the concentration–time curve from time 0 to infinity (AUC_INF), and terminal half-life (T _½), were derived from apixaban plasma concentration–time data. A general linear mixed-effect model analysis of C _max and AUC_INF was performed to estimate the effect of activated charcoal on apixaban exposure.

Results

A total of 18 subjects were treated and completed the study. AUC_INF for apixaban without activated charcoal decreased by 50 and 28 %, respectively, when charcoal was administered at 2 and 6 h post-dose. Apixaban C _max and T _max were similar across treatments. The mean T _½ for apixaban alone (13.4 h) decreased to ~5 h when activated charcoal was administered at 2 or 6 h post-dose. Overall, apixaban was well tolerated in this healthy population, and most adverse events were consistent with the known profile of activated charcoal.

Conclusion

Administration of activated charcoal up to 6 h after apixaban reduced apixaban exposure and facilitated the elimination of apixaban. These results suggest that activated charcoal may be useful in the management of apixaban overdose or accidental ingestion.     

Almorexant effects on CYP3A4 activity studied by its simultaneous and time-separated administration with simvastatin and atorvastatin

Purpose

To characterise further the previously observed cytochrome P450 3A4 (CYP3A4) interaction of the dual orexin receptor antagonist almorexant.

Methods

Pharmacokinetic interactions were investigated (n?=?14 healthy male subjects in two treatment groups) between almorexant at steady-state when administered either concomitantly or 2 h after administration of single doses of simvastatin (40 mg) or atorvastatin (40 mg).

Results

Almorexant dose-dependently increased simvastatin exposure (AUC_0–∞) when administered concomitantly [geometric mean ratios (90 % CI): 2.5 (2.1, 2.9) (100 mg), 3.9 (3.3, 4.6) (200 mg)], but not C_max [3.7 (3.0, 4.5) for both doses]. Time-separated administration resulted in relevant reductions of the interaction [AUC_0–∞: 1.4 (1.2, 1.7) (100 mg), 1.7 (1.5, 2.0) (200 mg); C_max: 1.5 (1.3, 1.9) (100 mg), 1.9 (1.6, 2.4) (200 mg)]. Similar results were obtained for hydroxyacid simvastatin. Independent of almorexant dose and relative time of administration, AUC_0–∞ and C_max of atorvastatin increased (ratios ranged from 1.1 to 1.5). AUC_0–∞ and C_max of o-hydroxy atorvastatin decreased dose-independently [AUC_0–∞: 0.8 (0.8, 0.9) (100 mg), 0.6 (0.5, 0.6) (200 mg); C_max: 0.3 (0.3, 0.4) (100 mg), 0.2 (0.2, 0.3) (200 mg)] when atorvastatin was concomitantly administered. C_max of o-hydroxy atorvastatin slightly decreased (0.8 for both doses) following time-separated administration; AUC_0–∞ was unchanged.

Conclusions

Whereas almorexant increased simvastatin exposure dose- and relative time of administration-dependently, atorvastatin exposure increased to a smaller extent and irrespective of dose and time. This suggests that the observed interaction of almorexant with simvastatin is mainly caused by intestinal CYP3A4 inhibition, whereas the interaction with atorvastatin is more due to hepatic CYP3A4 inhibition.     

Pharmacokinetic interactions of almorexant with midazolam and simvastatin, two CYP3A4 model substrates, in healthy male subjects

Purpose

Pre-clinical experiments have shown that almorexant, a dual orexin receptor antagonist, is able to inhibit cytochrome P450 3A4 (CYP3A4). Therefore, a study was conducted to investigate the effects of multiple-dose almorexant on the pharmacokinetics of midazolam and simvastatin, two CYP3A4 model substrates.

Methods

Fourteen healthy male subjects were enrolled in an open-label, randomized, two-way crossover study. Treatment period A consisted of a single oral dose of 2 mg midazolam on day 1 and 40 mg simvastatin on day 3. In treatment period B, subjects received 200 mg almorexant once daily for 9 days together with a single oral dose of midazolam on day 7 and simvastatin on day 9.

Results

Concomitant administration of midazolam with almorexant at steady-state levels, achieved within 4–5 days, resulted in an increase of 1.2-fold [90 % confidence interval (CI) 1.0–1.4], 1.4-fold (90 % CI 1.2–1.6), and 1.3-fold (90 % CI 1.2–1.4) in the maximum plasma concentration (C_max), area under the concentration–time curve from time 0 to infinity (AUC_0-∞), and terminal half-life (t_1/2), respectively, of midazolam; the time to peak plasma concentration (t_max) was unchanged. Whereas C_max and t_max were not influenced by almorexant, the AUC_0-∞ of hydroxy-midazolam increased by 1.2-fold (90 % CI 1.1–1.4) and the t_1/2 by 1.3-fold (90 % CI 1.0–1.5). Concomitant administration of simvastatin with almorexant at steady-state resulted in an increase of 2.7-fold (90 % CI 2.0–3.7) and 3.4-fold (90 % CI 2.6–4.4) in C_max and AUC_0-∞, respectively, for simvastatin; the t_1/2 and t_max were unchanged. The C_max and AUC_0-∞ of hydroxyacid simvastatin both increased by 2.8-fold, with 90 % CIs of 2.3–3.5 and 2.2–3.5, respectively; the t_max increased by 2 h and the t_1/2 was unchanged. The urinary 6-β-hydroxycortisol/cortisol ratio was unaffected by almorexant.

Conclusions

Our results suggest that the observed interaction was caused by the inhibition of CYP3A4 activity, most probably at the gut level.     

Lack of effect of continuous glycyrrhizin administration on the pharmacokinetics of the P-glycoprotein substrate talinolol in healthy volunteers

Purpose

To investigate the effects of repeated glycyrrhizin ingestion on the oral pharmacokinetics of talinolol, a probe drug for P-glycoprotein (P-gp) activity in humans.

Methods

Fourteen healthy adult male subjects were enrolled in a two-phase randomized crossover-design study. In each phase the volunteers received placebo or compound glycyrrhizin tablets (75 mg glycyrrhizin three times daily) for 6 days. On the seventh day, a single oral dose of 100 mg talinolol was administered, and blood samples were obtained to determine plasma talinolol concentrations, measured in plasma by high-performance liquid chromatography with an ultraviolet detector. Non-compartmental analysis was used to characterize talinolol plasma concentration–time profiles. All pharmacokinetics parameters were calculated using DAS ver. 2.1 software, and statistical analyses were performed with SPSS ver. 13.0 software. Analysis of variance was used to check the difference of the means of the pharmacokinetic parameters between the two treatments at a significance level of 0.05.

Results

All treatments were well tolerated during the study period. The geometric mean ± standard deviation of the AUC_0–∞ for talinolol treated by glycyrrhizin and talinolol treated by placebo was 2,218.3?±?724.3 and 1,988.2?±?649.2 ng·h/mL, respectively. The 90 % confidence intervals for the ratio of adjusted geometric means (glycyrrhizin:placebo) for AUC_0–∞ and C _max fell wholly within the interval [80, 125]. Six days of glycyrrhizin treatment resulted in no significant alterations in the pharmacokinetic parameters (AUC_0–∞, AUC_0–24, C _max, t _max, t _½) for talinolol.

Conclusions

Continuous glycyrrhizin administration had no induction effect on the expression of P-gp in our trial. Further research is needed to study the direct inhibition effect of glycyrrhizin on the function of P-gp with the simultaneous administration of both glycyrrhizin and P-gp substrate.     

No differences in the pharmacodynamics and pharmacokinetics of the thrombin receptor antagonist vorapaxar between healthy Japanese and Caucasian subjects

Background

Vorapaxar, a novel antiplatelet agent in advanced clinical development for the prevention and treatment of atherothrombotic disease, is a potent, orally bioavailable thrombin receptor antagonist selective for the protease-activated receptor 1 (PAR-1).

Methods

Since race/ethnicity may affect the safety, efficacy and dosage of drugs, this study was conducted to evaluate potential differences in the pharmacodynamics, pharmacokinetics and safety of vorapaxar after single (5, 10, 20, or 40?mg) or multiple (0.5, 1, or 2.5?mg once daily) doses in healthy Japanese and matched (gender, age, height, and weight) Caucasian volunteers.

Results

Vorapaxar was well tolerated in both Japanese and Caucasian subjects. Pharmacodynamic and pharmacokinetic profiles of vorapaxar in the two racial/ethnic groups were similar. In both racial groups, complete inhibition of platelet aggregation was achieved most rapidly with vorapaxar 40?mg and was consistently achieved and maintained with a 2.5?mg daily maintenance dose.

Conclusion

There were no substantial differences in the safety, pharmacokinetics or pharmacodynamics of vorapaxar between Japanese and Caucasian subjects.     

Preservation of Bioavailability of Ingredients and Lack of Drug-Drug Interactions in a Novel Five-Ingredient Polypill (Polycap™)

Background

The Polycap? (polypill; aspirin [acetylsalicylic acid], ramipril, simvastatin, atenolol, and hydrochlorothiazide) was found to be safe and effective for reducing multiple cardiovascular risk factors in The Indian Polycap? Study (TIPS).

Objective

We evaluated the bioavailability of each ingredient of the Polycap? and determined any drug-drug interactions relative to single component reference preparations.

Methods

The bioavailability of the ingredients of the Polycap? (T; test) when formulated as a single capsule was compared with that of identical capsules with each of its ingredients administered separately (R; reference) in a five-arm, randomized, single-dose, two-period, two-treatment, two-sequence, crossover trial with at least a 2-week washout period in a total of 195 healthy volunteers. Plasma concentrations of each drug and, where applicable, its active metabolite were measured using validated liquid chromatographytandem mass spectrometry and ultra-performance liquid chromatography. Mean pharmacokinetic parameters and their standard deviations were computed for each analyte.

Results

Comparative bioavailability was computed and no drug-drug interactions and no difference in comparative bioavailability were concluded for each ingredient based on point estimates of the T/R ratio of the geometric means falling within 80–125% for peak plasma concentration (C_max), area under the plasma concentration-time curve from time zero to the last measurable concentration (AUC_t), and AUC from time zero to infinity (AUC_∞). The T/R ratio for C_max, AUC_t and AUC∞ was within 80–125% for atenolol, hydrochlorothiazide, ramipril, ramiprilat and dose-normalized salicylic acid. However, for simvastatin, the T/R point estimates for C_max, AUC_t and AUC∞ for Ln-transformed data were significantly lower (～3–4%) than the lower bound of 80%. For its active metabolite, simvastatin acid, these estimates were significantly higher (～25–35%) than the higher bound of 125%. Thus, the increased bioavailability of active simvastatin acid appeared to compensate for the loss of bioavailability of simvastatin.

Conclusion

The Polycap? was found to be effective and safe in the previously published TIPS trial. The present study in healthy volunteers establishes that Polycap? is safe (no serious adverse events) and well tolerated, and that there is no indication of pharmacokinetic drug-drug interactions for any of the ingredients, with their bioavailabilities being well preserved.     

Effect of age and gender on pharmacokinetics and pharmacodynamics of a single ticagrelor dose in healthy individuals

Purpose

The aim of this study was to assess age and gender effects on ticagrelor pharmacokinetics and pharmacodynamics (PK/PD).

Methods

Forty healthy individuals [18–45?years (young); ≥65?years (elderly); ten men, ten women per age group) received 200?mg ticagrelor.

Results

Ticagrelor was rapidly absorbed [time to maximum concentration (C_max) (t_max) 2.5–3.0?h], and its major active metabolite, AR-C124910XX rapidly formed (t_max 3.0–3.5?h) in all groups. Ticagrelor exposure was higher in elderly vs. the young [area under the curve from time 0 to infinity (AUC_0-∞) 52%; C_max 63% higher] and women vs. men (AUC_0-∞ 37%; C_max 52% higher). Mean terminal elimination half-life was slightly longer in women vs. men but was unaffected by age. Similar results were observed for AR-C124910XX (elderly vs. young, AUC_0-∞ 48%; C_max 61% higher), and in women vs. men (AUC_0-∞ 55%; C_max 56% higher). Across all groups, ticagrelor produced substantial final-extent inhibition of platelet aggregation (IPA): >90% at 4 and 8?h postdose. Individuals with highest ticagrelor exposure (i.e., elderly) had the lowest IPA, indicating an age-related platelet sensitivity effect. In young individuals, platelet sensitivity was greater in men vs. women. Ticagrelor tolerability was not affected by age or gender.

Conclusions

Systemic exposures to ticagrelor and AR-C124910XX were higher in elderly vs. young and in women vs. men. Age- and gender-related changes in IPA were apparent, but substantial IPA was achieved in all groups. No adjustment in ticagrelor dose should be considered necessary based on age and gender.     

The pharmacokinetics and pharmacodynamics of prasugrel in healthy Chinese, Japanese, and Korean subjects compared with healthy Caucasian subjects

Purpose

Prasugrel is a novel thienopyridine prodrug metabolised to an active metabolite that binds irreversibly to the platelet P2Y₁₂ receptor and inhibits adenosine diphosphate (ADP)-induced platelet aggregation. We compared prasugrel pharmacokinetics, pharmacodynamics, and tolerability in healthy Chinese, Japanese, Korean and Caucasian subjects.

Methods

In an open-label, single-centre, parallel-design study, 89 healthy subjects (25 Chinese, 20 Japanese, 22 Korean and 22 Caucasian) aged 20–65 years were given a prasugrel 60-mg loading dose (LD) followed by daily 10-mg maintenance doses (MD) for 7 days and then 5-mg MD for 10 days. Plasma concentrations of prasugrel’s active metabolite and inhibition of ADP-induced platelet aggregation (IPA) were determined.

Results

Mean exposure to prasugrel’s active metabolite in all treatment regimens was higher in each of the Asian groups than in the Caucasian group, although there was considerable overlap between individual exposure estimates in Asians and Caucasians. The mean IPA was also higher in Asians than in Caucasians following a prasugrel 60-mg LD, although the difference did not consistently achieve statistical significance. Prasugrel 10-mg or 5-mg MD produced statistically significantly higher IPA in each Asian group compared with that in the Caucasians. Prasugrel was well tolerated during the LD and MD regimens by all groups.

Conclusions

Mean exposure to the prasugrel active metabolite following prasugrel 60-mg LD and during daily 10-mg or 5-mg MD was higher in each of the Asian groups than in the Caucasian group, which resulted in greater platelet inhibition.     

Tolerability and Pharmacokinetics of Ranolazine Following Single and Multiple Sustained-release Doses in Chinese Healthy Adult Volunteers

Background and Objectives

Ranolazine was approved by the US Food and Drug Administration in January 2006 for the treatment of chronic angina pectoris, and is the first approved agent from a new class of anti-anginal drugs in almost 25 years. The primary objective of this study was to determine the concentration of ranolazine in human plasma using the liquid chromatography/tandem mass spectrometry (LC-MS/MS) method and to compare the pharmacokinetic properties of ranolazine after administration of single and multiple doses of ranolazine in healthy Chinese adult volunteers.

Methods

A randomized, open-label, single- and multiple-dose study design was used in the study. Subjects were randomized to receive a single dose of 500, 1,000, or 1,500 mg of ranolazine. Those who received the single dose continued on to the multiple-dose phase and received 500 mg twice daily for 7 days. In the single-dose phase, blood samples were collected from 0 to 48 h after drug administration. In the multiple-dose phase, samples were obtained before drug administration at 8:00 am and 8:00 pm on days 6 and 7 to determine the minimum steady-state plasma concentration (C_min,ss) of ranolazine; on day 8, samples were collected from 0 to 48 h after drug administration. All values were expressed as means (standard deviations [SDs]). Adverse events (AEs) were monitored throughout the study via subject interview, vital signs, and blood sampling.

Results

The LC-MS/MS method was developed and validated. Twelve Chinese subjects (six men, six women) were enrolled in the single-dose phase of the pharmacokinetic study. The mean (SD) age of the subjects was 24.7 (1.6) years; their mean (SD) weight was 61.3 (6.4) kg, their mean (SD) height was 165.7 (4.5) cm, and their mean (SD) body mass index was 21.6 (6.6) kg/m². The main pharmacokinetic parameters [mean (SD)] for ranolazine after administration of a single oral dose of 500, 1,000, and 1,500 mg were as follows: maximum plasma concentration (C_max) 741.5 (253.0), 1,355.0 (502.0), and 2,328.7 (890.5) ng/mL, respectively; area under the concentration–time curve from time zero to 48 h (AUC₄₈) 9,071.9 (3,400.0), 16,573.5 (6,806.2), and 29,324.5 (10,857.2) ng·h/mL; AUC from time zero extrapolated to infinity (AUC_∞) 9,826.7 (3,152.0), 16,882.4 (6,790.8), and 29,923.5 (10,706.3) ng·h/mL; time to reach C_max (t_max) 5.3 (1.4), 4.2 (1.2), and 5.9 (2.8) h; elimination half-life (t_½) 6.4 (3.3), 6.4 (3.5), and 6.7 (4.3) h. Mean (SD) values for the main pharmacokinetic parameters for ranolazine after administration of multiple doses were as follows: steady-state C_max (C_max,ss) 1,732.9 (547.3) ng/mL; C_min,ss 838.1 (429.8) ng/mL; steady-state AUC at time t (AUC_ss,(t)) 14,655.5 (5,624.2) ng·h/mL; average steady-state plasma drug concentration during multiple-dose administration (C_av,ss) 1,221.3 (468.7) ng/mL; t_max 3.46 (1.48) h; t_½ 6.28 (2.48) h.

Conclusion

In this group of healthy Chinese subjects, AUC and C_max increased proportionally with the dose, whereas t_½ was independent of the dose. The pharmacokinetic properties of ranolazine were linear after administration of single oral doses of 500 to 1,500 mg. Compared with the pharmacokinetic parameters of the subjects who received a single dose, those who received multiple doses (twice daily) of ranolazine had a larger AUC from time zero to the time of the last measurable concentration (AUC_last), AUC_∞, C_max, and apparent total body clearance of drug from plasma after oral administration (CL/F), and shorter t_max (all p < 0.05). Furthermore, some of the main pharmacokinetic parameters of ranolazine may reflect ethnic differences. This dosage was generally well tolerated by all the subjects.     

Pharmacokinetic–Pharmacodynamic Relationships of Macitentan,a New Endothelin Receptor Antagonist,After Multiple Dosing in Healthy Korean Subjects

Background and objectives

Macitentan is a novel dual endothelin (ET)-1 receptor antagonist to be used in patients with pulmonary arterial hypertension. This study aimed to assess the pharmacokinetics (PK) and pharmacodynamics (PD) of macitentan after administration of multiple doses to healthy Korean male subjects.

Methods

A randomized, double-blind, placebo-controlled, multiple-ascending dose study was performed in 30 healthy male subjects receiving oral macitentan (3, 10, or 30 mg) or placebo once daily for 10 days. Plasma concentrations of macitentan, its active metabolite ACT-13277, and ET-1 were evaluated. Safety and tolerability measurements were conducted throughout the study.

Results

The concentration–time profile of macitentan was characterized by slow absorption (median time to maximum plasma concentration [t _max] 9–10 h) and slow elimination (mean elimination half-life [t _½] 11–15 h). After repeated doses of 3, 10, and 30 mg of macitentan over the course of 10 days, the peak concentration (C _max) increased as the dose increased and the area under the plasma concentration–time curve during the dosing interval (AUC _τ ) increased in a dose-proportional manner. Plasma concentrations showed approximately 1.5- to 1.9-fold accumulation on day 10 compared with day 1. ACT-132577 showed higher levels of exposure than macitentan, its mean half-life was 46–48 h, and it accumulated 7- to 12-fold. Macitentan increased plasma ET-1 concentrations at all doses tested and was well tolerated and elicited no serious adverse events.

Conclusion

Multiple oral doses of 3, 10, and 30 mg of macitentan were well tolerated in healthy Korean subjects, and its pharmacokinetics correlated positively with ET-1 concentrations.     

Tolvaptan: the evidence for its therapeutic value in acute heart failure syndrome

Introduction:

Acute heart failure syndrome (AHFS) is one of the leading causes of hospital admission in the US. Tolvaptan is a vasopressin V₂ receptor antagonist that blocks the effect of arginine vasopressin (AVP) in reabsorbing water from the collecting ducts of the nephrons in congestive heart failure.

Aims:

To review the evidence for utilizing tolvaptan in the treatment of AHFS.

Evidence review:

Several clinical trials have sought to assess the clinical effects of tolvaptan in heart failure. Compared with placebo, tolvaptan has been shown to reduce bodyweight and improve serum sodium in patients with AHFS without worsening renal function. Tolvaptan appeared to be well tolerated with a good safety profile. It caused a significant reduction in pulmonary capillary wedge pressure compared with placebo, but has yet to demonstrate reversal of cardiac remodeling. A large-scale mortality trial showed no differences in long-term mortality rates between tolvaptan and placebo, although early symptom relief was apparent with tolvaptan and lower diuretic use.

Place in therapy:

Tolvaptan has shown to be safe and effective in treating congestion in AHFS. Free water excretion in fluid-overloaded patients vulnerable to cardiorenal compromise with standard diuretic therapy makes V₂ vasopressin receptor blockade an attractive adjunct to standard medical therapy aimed at reducing congestion in AHFS.     

Pharmacokinetics,Tolerability, and Safety of the Single Oral Administration of AGSAV301 vs Exforge: A Randomized Crossover Study of Healthy Male Volunteers

Background and Objective

Valsartan, an angiotensin receptor blocker, is often used with calcium channel blockers (CCBs) such as amlodipine to control hypertension. Recently, the fixed-dose combination (FDC) of amlodipine 10 mg/valsartan 160 mg (Exforge) was approved. Amlodipine is a racemic mixture of CCB; S-amlodipine has higher activity than R-form. Therefore, AGSAV301, the FDC of S-amlodipine 5 mg/valsartan 160 mg was recently developed. The objective of this study was to compare the pharmacokinetic (PK) characteristics of S-amlodipine and valsartan when administered as one tablet each of Exforge and AGSAV301 to healthy male subjects.

Methods

This was a single-dose, randomized, open-label, two-way, two-period crossover study. Each subject received a single dose of AGSAV301 and Exforge, separated by a 3-week washout period. Plasma samples for the PK analysis of valsartan and S-amlodipine were collected at predose (0) and 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 16, 24, 36, 48, 72, 96, 120, and 168 h after administration. Tolerability was also evaluated.

Results

A total of 29 subjects were enrolled; 24 completed this study. The S-amlodipine maximum plasma concentration (C _max) geometric mean ratio (GMR) between AGSAV301 and Exforge was 0.951 (90 % CI 0.983–1.014), and area under the concentration–time curve from time 0 to last measured time point (AUC_last) was 0.917 (90 % CI 0.861–0.976). The GMR of valsartan C _max was 0.994 (90 % CI 0.918–1.076), and the AUC_last was 0.927 (90 % CI 0.821–1.047). All adverse events (AEs) were resolved without sequelae; no serious AEs were reported. Two drugs showed similar tendencies to lower blood pressure in healthy subjects.

Conclusions

The PK profiles of AGSAV301 and Exforge were bioequivalent. Both drugs were also well tolerated, with comparable AE profiles and similar blood pressure-lowering tendencies in healthy volunteers, suggesting equivalent therapeutic indications.     

Pharmacokinetic and pharmacodynamic interactions between the hepatitis C virus protease inhibitor,boceprevir, and the oral contraceptive ethinyl estradiol/norethindrone

Purpose

The purpose of this study was to examine drug interactions between boceprevir, a hepatitis C virus NS3/4A protease inhibitor, and a combined oral contraceptive containing ethinyl estradiol (EE) and norethindrone (NE).

Methods

A single-center, open-label study was conducted in 20 healthy female volunteers. In three consecutive 28-day treatment periods, subjects received EE/NE (0.035 mg/1 mg; 21 days on, 7 days off). During period 3, subjects also received boceprevir (800 mg three times daily) for 28 days.

Results

Coadministration of boceprevir with EE/NE did not affect NE AUC_0–24 but slightly reduced NE C _max. Geometric mean ratios (GMRs) for NE AUC_0–24 and C _max with EE/NE alone and EE/NE plus boceprevir were 0.96 (90 % confidence interval (CI), 0.87–1.06) and 0.83 (90 % CI, 0.76–0.90). Coadministration of boceprevir with EE/NE reduced EE AUC_0–24 and C _max by 26 and 21 %, with GMRs of 0.74 (90 % CI, 0.68–0.80) and 0.79 (90 % CI, 0.75–0.84). Boceprevir had no effect on mid-cycle luteinizing hormone (LH), follicle-stimulating hormone (FSH), or sex hormone-binding globulin levels, and progesterone concentrations remained <1 ng/ml during the luteal phase. Adverse events reported in this study were consistent with the well-established safety profile of boceprevir.

Conclusion

Serum progesterone, LH, and FSH levels indicate that ovulation was suppressed during coadministration of boceprevir with EE/NE. Coadministration of boceprevir with combined oral contraceptives containing EE and ≥1 mg of NE is therefore unlikely to alter contraceptive effectiveness. The ovulation suppression activity of oral contraceptives containing lower doses of NE, and of other forms of hormonal contraception during coadministration with boceprevir, has not been established.     

In Vivo Absorption and Disposition of Cefadroxil After Escalating Oral Doses in Wild-Type and PepT1 Knockout Mice

Purpose

To determine the effect of PepT1 on the absorption and disposition of cefadroxil, including the potential for saturable intestinal uptake, after escalating oral doses of drug.

Methods

The absorption and disposition kinetics of [³H]cefadroxil were determined in wild-type and PepT1 knockout mice after 44.5, 89.1, 178, and 356 nmol/g oral doses of drug. The pharmacokinetics of [³H]cefadroxil were also determined in both genotypes after 44.5 nmol/g intravenous bolus doses.

Results

PepT1 deletion reduced the area under the plasma concentration-time profile (AUC_0-120) of cefadroxil by 10-fold, the maximum plasma concentration (C_max) by 17.5-fold, and increased the time to reach a maximum plasma concentration (T_max) by 3-fold. There was no evidence of nonlinear intestinal absorption since AUC_0-120 and C_max values changed in a dose-proportional manner. Moreover, the pharmacokinetics of cefadroxil were not different between genotypes after intravenous bolus doses, indicating that PepT1 did not affect drug disposition. Finally, no differences were observed in the peripheral tissue distribution of cefadroxil (i.e., outside gastrointestinal tract) once these tissues were corrected for differences in perfusing blood concentrations.

Conclusions

The findings demonstrate convincingly the critical role of intestinal PepT1 in both the rate and extent of oral administration for cefadroxil and potentially other aminocephalosporin drugs.     

Does a Hot Drink Provide Faster Absorption of Paracetamol Than a Tablet? A Pharmacoscintigraphic Study in Healthy Male Volunteers

Purpose

To investigate the hypothesis that paracetamol is absorbed faster from a hot drink than from a standard tablet using simultaneous scintigraphic imaging and pharmacokinetic sampling.

Methods

Twenty-five healthy male volunteers received both paracetamol formulations in a randomised manner. The formulation administered in the first treatment arm was radiolabelled to allow scintigraphic monitoring. In both treatment arms, blood samples were taken for assessing paracetamol absorption.

Results

Following the hot drink, paracetamol absorption was both significantly faster and greater over the first 60 min post-dose compared with the tablet, as evidenced by the median time to reach t_0.25?μg/mL of 4.6 and 23.1 min, respectively, and AUC_0-60 of 4668.00 and 1331.17 h*ng/mL, respectively. In addition, t_max was significantly shorter for the hot drink (median time = 1.50 h) compared with the tablet (1.99 h). However, C_max was significantly greater following the tablet (9,077 ng/mL) compared with the hot drink (8,062 ng/mL). Onset of gastric emptying after the hot drink was significantly faster than after the standard tablet (7.9 versus 54.2 min), as confirmed scintigraphically.

Conclusions

Compared with a standard tablet, a hot drink provides faster absorption of paracetamol potentially due to more rapid gastric emptying.     

Rationale and conditions for the requirement of chiral bioanalytical methods in bioequivalence studies

Purpose

The aim of the present work was to assess the need for chiral bioanalytical methods in bioequivalence studies.

Methods

The samples from a bioequivalence study of two ibuprofen 2% oral suspensions that had shown bioequivalence for AUC and C_max, but not for t_max (medians of 2.0 and 0.75 h) with a non-chiral method were assayed with a chiral method to investigate whether there was an actual difference in the rate of absorption within the limits of C_max and AUC bioequivalence.

Results

The non-chiral method and the sum of concentrations of both enantiomers obtained with the chiral method gave a similar outcome (90% CI C_max non-chiral: 82.77–96.09, sum of enantiomers: 82.19–98.23; 90% CI AUC_t non-chiral: 107.23–115.49, sum of enantiomers: 105.73–121.35). However, the chiral method showed differences in AUC and C_max that resulted in non-bioequivalence for the individual enantiomers (90% CI C_max S-ibuprofen: 76.05–91.36, R-ibuprofen: 87.84–113.05; 90% CI AUC_t S-ibuprofen: 96.67–105.86, R-ibuprofen: 118.86–142.24). The differences in the pharmacokinetics of each enantiomer, and thus in the enantiomer concentration ratio, were dependent on the rate of absorption.

Conclusions

Due to the fact that in bioequivalence studies the rate of absorption of the new product is unknown, chiral bioanalytical methods should be employed for chiral drugs, such as ibuprofen, whose enantiomers exhibit different pharmacodynamic characteristics and whose enantiomer concentration ratio might be modified by the rate of absorption, irrespective of whether the eutomer is the minor enantiomer or the similarity of the pharmacokinetics of the enantiomers at a given rate of absorption.     

Effects of enzyme inducers efavirenz and tipranavir/ritonavir on the pharmacokinetics of the HIV integrase inhibitor dolutegravir

Purpose

Dolutegravir (DTG) is an unboosted, integrase inhibitor for the treatment of HIV infection. Two studies evaluated the effects of efavirenz (EFV) and tipranavir/ritonavir (TPV/r) on DTG pharmacokinetics (PK) in healthy subjects.

Methods

The first study was an open-label crossover where 12 subjects received DTG 50 mg every 24 hours (q24h) for 5 days, followed by DTG 50 mg and EFV 600 mg q24h for 14 days. The second study was an open-label crossover where 18 subjects received DTG 50 mg q24h for 5 days followed by TPV/r 500/200 mg every 12 hours (q12h) for 7 days and then DTG 50 mg q24h and TPV/r 500/200 mg q12h for a further 5 days. Safety assessments and serial PK samples were collected. Non-compartmental PK analysis and geometric mean ratios and 90 % confidence intervals were generated.

Results

The combination of DTG with EFV or TPV/r was generally well tolerated. Four subjects discontinued the TPV/r study due to increases in alanine aminotransferase that were considered related to TPV/r. Co-administration with EFV resulted in decreases of 57, 39 and 75 % in DTG AUC_(0–τ), C _max and C _τ , respectively. Co-administration with TPV/r resulted in decreases of 59, 46 and 76 % in DTG AUC_(0–τ), C _max and C _τ , respectively.

Conclusions

Given the reductions in exposure and PK/pharmacodynamic relationships in phase II/III trials, DTG should be given at an increased dose of 50 mg twice daily when co-administered with EFV or TPV/r, and alternative regimens without inducers should be considered in integrase inhibitor-resistant patients.