Pharmacology, toxicology and human pharmacokinetics of tropisetron.

Tropisetron is a novel, potent and highly selective 5-HT3 receptor antagonist, which is active in the treatment of nausea and vomiting induced by highly emetogenic chemotherapeutic drugs such as cisplatin. Tropisetron selectively blocks the excitation of the presynaptic 5-HT receptors of the peripheral neurones involved in the emetic reflex, and may have other direct actions in the CNS on 5-HT3 receptors, mediating the actions of vagal inputs to the area postrema. Toxicological studies show that tropisetron is generally well tolerated by all animal species investigated and no specific organ toxicity was observed, other than slight loss of body weight development. In man, tropisetron metabolism is linked to the cytochrome P-450 2D6 isoenzyme system, which determines the polymorphism of debrisoquine/sparteine metabolism. As a result, there are phenotypical populations of extensive and poor metabolizers. The two main adverse events in human volunteer tolerability studies with tropisetron were headache and constipation. These adverse events tended to be slightly more intense and to last longer in poor metabolizers, compared with extensive metabolizers. Tropisetron had similar pharmacokinetic characteristics in elderly patients and renal patients, compared with healthy subjects. From a toxicological and pharmacokinetic point of view, therefore, daily doses of 5 mg tropisetron can be administered to both poor and extensive metabolizers, as well as to special populations, without any particular precautions.