Aging and drug disposition--metabolism.

The kinetics of drugs are known to change in the elderly. The most unequivocal example is the decrease in renal drug clearance. Yet, few studies have been published on the renal clinically important impairment of drug metabolism occurs in the elderly, and the effect of age per se cannot easily be discerned because a number of other factors that affect drug metabolism change with age (dietary and smoking habits, disease, drug interactions, ect.). In each age group there is a marked interindividual variation in the metabolic clearance of drugs leading to pronounced differences in steady-state plasma concentrations at fixed dosage-schedules. For drugs with a narrow therapeutic range it is important to avoid standard doses in slow metabolizers. This phenotype is at risk to develop adverse drug reactions unless the dose is reduced. It may be particularly important to recognize the slow metabolizer phenotype among the elderly, who may have exaggerated drug response due to physiological and pharmacodynamic reasons.