Using pharmacokinetics in drug therapy. VII: Pharmacokinetic factors influencing drug therapy in the aged.

The pharmacokinetic factors influencing drug therapy in the elderly are reviewed with special attention on dosage regimens. Deterioration in the effectiveness of drug clearance appears to be the principal pharmacokinetic factor that is altered with age. Prolonged half-life and reduced volume of distribution are the primary and secondary causes, respectively, of the altered clearance. Studies relating age to changes in the pharmacokinetics of propranolol, digoxin, quinidine, warfarin, lithium, benzodiazepines, theophylline, cimetidine, phenytoin, and kanamycin are reviewed. Decreased drug clearance in the elderly may merit a compensatory reduction in dosage, especially for drugs with a narrow therapeutic index.