Steady-state plasma concentrations of mianserin and its major active metabolite, desmethylmianserin

The steady-state plasma concentrations of mianserin and its major active metabolite, desmethylmianserin, were measured in 76 depressed patients receiving 30 mg of mianserin at bedtime. There were considerable inter-individual variations in the steady-state plasma concentrations of these compounds; the plasma concentrations of mianserin plus desmethylmianserin were within the therapeutic range suggested previously by us in only 43% of the patients. With advancing age, the plasma concentrations of mianserin increased significantly, while those of mianserin plus desmethylmianserin remained unchanged. Sex, smoking, and coadministration of benzodiazepines did not affect the drug's metabolism. There was no evidence that the kinetics of these compounds were nonlinear with increasing doses. The present study thus suggests that measuring the plasma concentrations of mianserin and desmethylmianserin contributes to rational treatment with this drug, that age, sex, smoking, and coadministration of benzodiazepines are not important factors in determining the dose, and that these compounds have linear kinetics.