Pharmacokinetics of the selective serotonin reuptake inhibitors

The pharmacokinetic properties of the newer specific serotonin (5-HT) reuptake inhibitors are reviewed. Fluoxetine, paroxetine, sertraline, and fluvoxamine show kinetic characteristics similar to those of the older tricyclic antidepressants. They are well absorbed orally but exhibit an extensive first-pass extraction in the liver. They are widely distributed in body tissues and highly bound to plasma proteins. The clearance of these drugs by the body is accomplished almost entirely by hepatic metabolism. Fluoxetine and sertraline both produce a pharmacologically active metabolite, although insufficient data are available to evaluate the clinical significance of desmethylsertraline. With the exception of fluoxetine, which has an elimination half-life of 2 to 3 days, the other drugs have half-lives of about 1 day. Available data indicate that paroxetine and fluvoxamine achieve steady state within 4 to 14 days of chronic dosing, whereas for fluoxetine, and particularly norfluoxetine, steady state is not reached for weeks. The pharmacokinetics of these drugs are characterized by marked intersubject variability. Only preliminary data are available on steady-state plasma concentrations achieved during treatment and correlations to therapeutic or adverse effects.