Assessment of CYP2D6 activity in very elderly healthy subjects

Effect of Gender and Age on the Pharmacokinetics of Repinotan

OBJECTIVE

Repinotan hydrochloride (repinotan) is a selective, high-affinity, full serotonin receptor agonist at the 5-HT(1A) subtype that is undergoing clinical development in acute stroke. To investigate whether gender is an important covariable for repinotan pharmacokinetics, two studies were performed in subjects of different age and gender who had been phenotyped as extensive metabolisers for cytochrome P450 (CYP)2D6 using dextromethorphan as model substrate.

SUBJECTS AND METHODS

Both studies were placebo-controlled, double-blind, randomised, parallel-group studies. Study I was conducted in six healthy young males, five healthy elderly males, and four healthy elderly females receiving a continuous intravenous (IV) infusion of repinotan 0.45 microg/kg/h or placebo for a duration of 12 hours. Study II was performed in healthy elderly male and female volunteers aged >/=65 years with 67 subjects receiving repinotan and 34 receiving placebo. Subjects received a 12-hour infusion of repinotan at doses of 0.1, 0.3, 0.5, 1.0, 2.0 or 3.0 microg/kg/h.

RESULTS

Following IV infusion, the steady-state plasma concentration (C(ss)) for repinotan was reached after 4-6 hours consistent with its half-life of 0.8-1.8 hours. In both male and female subjects, the volume of distribution at steady-state and plasma clearance (CL) were independent of dose, indicating linear pharmacokinetics and dose-proportionality for area under the concentration-time curve (AUC) and peak plasma concentration (C(max)) over the dose range of 0.1-3.0 microg/kg/h. Compared with elderly subjects, repinotan CL was unchanged in a subgroup of young subjects. The pooled evaluation of elderly subjects (n = 67) showed that gender had no influence on the pharmacokinetics of repinotan. The ratios male : female and their 90% CIs were: 0.91 (0.789, 1.052) for dose/bodyweight-normalised C(max) (C(max,norm)), 0.95 (0.808, 1.110) for half-life, 0.97 (0.900, 1.044) for V(ss,) and 1.11 (0.923, 1.336) for CL.

CONCLUSION

These results indicate that gender does not affect the pharmacokinetics of repinotan in healthy subjects whose age (>/=65 years) was representative of the target patient population for repinotan in acute stroke.

Drug metabolism and drug interactions in the elderly

In the elderly concomitant use of several drugs (polypharmacy) is very common. Thus, the risk for drug interactions might be increased in this population. Since most drugs are hepatically eliminated by various metabolic pathways, liver function has to be considered as an additional factor modifying drug response. This chapter focuses on the hepatic mechanisms of interactions, especially on various inhibitors and inducers of the most important cytochrome P450 isoenzymes involved in drug metabolism. In addition, age-dependent changes in liver function are addressed. Based on pharmacokinetic results with different probe drugs, some inconsistencies in this area are discussed. The most important metabolic drug-drug interactions are independent of the age of the patients. However, since elderly patients consume a greater proportional share of drugs, they represent a population at risk for interactions. Awareness of this clinical problem may help to diminish those risks.