Tropisetron

Indications

Tropisetron is primarily indicated for the prevention of nausea and vomiting associated with cytotoxic chemotherapy and surgical procedures. Its effectiveness in managing these symptoms makes it a vital component in treatment protocols that involve agents known to induce these side effects.

Absorption

The absorption characteristics of Tropisetron are noteworthy, as it is rapidly assimilated from the gastrointestinal tract, with a mean half-life of approximately 20 minutes, and absorption is nearly complete at over 95%. Despite this efficient absorption, the drug undergoes significant first-pass metabolism in the liver, resulting in an absolute bioavailability of 60% for a 5 mg oral dose. Tropisetron reaches its peak plasma concentration within three hours post-administration.

Metabolism

Tropisetron undergoes metabolic transformation primarily through hydroxylation at the 5, 6, or 7 positions on its indole ring, followed by conjugation with glucuronide or sulphate, and is subsequently excreted in urine or bile. The urine-to-feces excretion ratio is approximately 5:1. Notably, the metabolites exhibit significantly reduced potency at the 5-HT3 receptor and thus do not substantially contribute to the drug's overall pharmacological effects.

Mechanism of Action

Tropisetron functions by competitively binding to and inhibiting serotonin activity at 5HT3 receptors, both on the vagus nerve terminals in the gastrointestinal (GI) tract and centrally within the chemoreceptor trigger zone (CTZ) of the area postrema in the central nervous system (CNS). This mechanism effectively suppresses nausea and vomiting associated with chemotherapy and radiotherapy treatments.