In poor metabolizers of sparteine/debrisoquine (about 8% of the Caucasian population) the elimination half-life of tropisetron is prolonged (4-5 times longer than in extensive metabolizers). Studies indicate that, for 6-day courses in patients with poor metabolism, the usual daily dose of 5 mg does not need to be reduced. No change in the pharmacokinetics of tropisetron occurs in acute hepatitis or fatty liver disease. In contrast, liver cirrhosis or impaired kidney function may have plasma concentrations up to 50% higher than those found in healthy volunteers belonging to the group of extensive metabolizers of sparteine/debrisoquine. Nevertheless, no dosage reduction is necessary in such patients when recommended 6-day courses of 5 mg tropiseron per day are given. In uncontrolled hypertension, daily doses of tropiseron higher than 10 mg should be avoided, since they may cause further increase in blood pressure. Caution should be exercised in cardiac rhythm or conduction disturbances, or in patients treated with anti-arrhythmic or β-adrenergic-blocking agents, since in these patient groups limited experience is available with concurrent use of tropiseron and anesthetics.