Effect of Multiple-Dose Diltiazem on the Pharmacokinetics of the Renin Inhibitor ACT-077825

Population Pharmacokinetic Modeling of Diltiazem in Chinese Renal Transplant Recipients

BACKGROUND AND OBJECTIVES

Diltiazem is a benzothiazepine calcium blocker and widely used in renal transplant patients since it improves the level of tacrolimus or cyclosporine A concentration. Several population pharmacokinetic (PopPK) models had been established for cyclosporine A and tacrolimus but no specific PopPK model was established for diltiazem. The aim of the study is to develop a PopPK model for diltiazem in renal transplant recipients and provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study.

METHODS

Patients received tacrolimus as primary immunosuppressant agent after renal transplant and started administration of diltiazem 90 mg twice daily on 5th day. The concentration of diltiazem at 0, 0.5, 1, 2, 8, and 12 h was measured by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Genotyping for CYP3A4*1G, CYP3A5*3, and MDR1 3435 was conducted by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). 25 covariates were considered in the stepwise covariate model (SCM) building procedure.

RESULTS

One-compartment structural pharmacokinetic model with first-order absorption and elimination was used to describe the pharmacokinetic characteristics of diltiazem. Total bilirubin (TBIL) influenced apparent volume of distribution (V/F) of diltiazem in the forward selection. The absorption rate constant (K _a), V/F, and apparent oral clearance (CL/F) of the final population pharmacokinetic (PopPK) model of diltiazem were 1.96/h, 3550 L, and 92.4 L/h, respectively.

CONCLUSION

A PopPK model of diltiazem is established in Chinese renal transplant recipients and it will provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study.

Single-dose pharmacokinetics of the renin inhibitor ACT-077825 in elderly and young subjects of both sexes

BACKGROUND/AIMS

The study objective was to investigate and compare the pharmacokinetics of a single oral dose of ACT-077825, a novel direct renin inhibitor, in young and elderly, male and female healthy subjects and to evaluate the safety and tolerability of ACT-077825 in these population groups.

METHODS

A total of 32 healthy subjects were included in this single-center, open-label study. The subjects were divided into 4 groups, including 8 young male, 8 young female, 8 elderly male and 8 elderly female subjects. Each participant received a single 200-mg dose of ACT-077825. Blood samples were taken over 5 days (120 h) to determine the plasma levels of ACT-077825. Safety and tolerability were monitored using standard assessments before drug administration, on the administration day and at the end of the blood sampling period.

RESULTS

Upon pooling male and female subjects, exposure was higher in elderly compared to young subjects, showing an increase of 65% for AUC0-∞, 40% for Cmax and 38% for t1/2. While young male and female subjects showed similar plasma profiles and exposure, a significant increase in exposure occurred with age in both sexes compared to younger subjects. The difference was largest between young and elderly females. Furthermore, the exposure to ACT-077825 was around 30% higher in elderly female compared to elderly male subjects. ACT-077825 was well tolerated by all groups, including the elderly females who showed the highest exposure.

CONCLUSIONS

ACT-077825 exposure is moderately increased in elderly subjects. The clinical relevance of this observation should be explored in the context of further studies.