PHARMACOKINETICS OF PSYCHOTROPIC-DRUGS IN SPECIAL POPULATIONS

Patients treated for psychiatric illness may have a variety of charact eristics that alter the pharmacokinetic profiles of psychotropic drugs . Genetic background, age, health status, and personal habits can chan ge the body's ability to absorb, distribute, and metabolize medication s. Most psychotropic drugs, with the exception of lithium, are elimina ted via biotransformation in the liver rather than renal excretion, an d a number of studies have demonstrated distinct phenotypes for hepati c metabolism involving the cytochrome P450 system. ''Slow'' metabolize rs are likely to develop higher plasma concentrations of several diffe rent classes of psychotropic drugs, including tricyclic antidepressant s. Advancing age reduces renal function but has little effect on hepat ic metabolism. Volume of distribution may also be increased in elderly patients because of their greater percentage of adipose tissue. Ethni c background can significantly influence both drug metabolism and the pharmacodynamics of a variety of drugs. Thus, the physician should car efully consider patient characteristics when prescribing psychotropic medications and should engage in therapeutic drug monitoring when ther e is any doubt about the plasma drug levels that a given dosing regime n will achieve.