Pharmacokinetic and pharmacodynamic characteristics of trazodone in the elderly.

The pharmacokinetic and some pharmacodynamic characteristics of a single oral dose of 100 mg trazodone were compared in young and elderly volunteers. The maximum plasma concentration of trazodone was similar in both age groups. The time to maximum concentration was apparently prolonged in four subjects who swallowed the capsule with a minimal volume of fluid. This may have been due to the capsule being retained in the oesophagus. The terminal phase half-life of trazodone was significantly prolonged (P less than 0.05) and area under the plasma concentration-time curve was significantly larger (P less than 0.01) in the elderly. Apparent oral clearance was significantly reduced (P less than 0.01) in the elderly. Measurement of critical flicker fusion threshold and subjective assessment of alertness using a visual analogue scale, confirmed the sedative effect of trazodone in both age groups. The elderly subjects were less alert for a longer period following drug administration than the young. The differing pharmacokinetic and pharmacodynamic characteristics of trazodone in the young and elderly may be due to an age-related reduction in hepatic drug-metabolising activity, a difference in regional distribution or a change in CNS sensitivity to the drug.