Pharmacological aspects of mianserin.

S(+)-mianserin is the more potent enantiomer of mianserin in pharmacological tests indicative for antidepressant activity. Pharmacological tests indicative for sedation suggest that sedative effects are similar for mianserin and its enantiomers. Racemic mianserin had the optimal therapeutic ratio of antidepressant-like activity versus sedative properties when assessed by computerised EEG in healthy volunteers participating in a double-blind placebo-controlled single dose trial. Of the known metabolites, desmethylmianserin and 8-hydroxymianserin substantially retain pharmacological properties indicative for antidepressant activity but are less active than mianserin in tests indicative for sedation. Mianserin-N-oxide is inactive or only weakly active in most pharmacological tests. Desmethylmianserin occurs in human plasma after both single and multiple dosage to an extent of about one-third that of mianserin. Mianserin has optimal clinical efficacy as the racemate. Desmethyl-mianserin and 8-hydroxymianserin are pharmacologically active metabolites and may contribute to the overall antidepressant effects of mianserin.