Safety evaluation of ritanserin--an investigational serotonin antagonist.

Ritanserin is an investigational serotonin-S2 receptor antagonist with activity in a variety of psychiatric disturbances characterized by dysthymia or anxiety. This investigation evaluates acute safety and tolerability of ritanserin in 12 healthy males. Ritanserin 10 mg, 20 mg, and placebo were administered as single doses in a randomized, double-blind, crossover fashion. Treatment effects on vital signs, laboratory tests, a mood evaluation test, electrocardiograms (ECGs), and reported adverse experiences were monitored. Plasma levels were determined at two hours postdose. Results indicated no clinically relevant effects on vital signs, laboratory tests, ECGs, or mood evaluations. Dose proportionality was demonstrated. The incidence of total adverse effects (primarily somnolence and fatigue) after single-dose administration was 25 percent for placebo, 75 percent for 10 mg, and 81.8 percent for 20 mg. There was a relationship between incidence of adverse effects and dose, but no general correlation between plasma levels and severity of adverse experiences. The results indicate that ritanserin is safe and tolerable following acute administration of 10 mg and 20 mg oral doses.