Granisetron hydrochloride (Granisetron HCl) is a serotonin receptor (5HT-3 selective) antagonist that has been used as an antiemetic for cancer chemotherapy patients.

Granisetron blocks the delayed rectifier current (IK) of feline isolated ventricular myocytes with a KD of 4.3 mM. Granisetron shows an intrinsic voltage-dependence as the block increases with depolarization. Granisetron blocks from the intracellular side at a binding site located 10% across the transmembrane electrical field. Granisetron (3 mM) prolongs the action potential duration (APD) by about 30% at 0.5 Hz in feline isolated ventricular myocytes. [1] Granisetron but not Ondansetron, could prevent the activation of putative 5-H; autoreceptors, thus leading to a decrease in serotonin release by the enterochromaffin cells. [2]

Granisetron provides a substantial benefit against cisplatin-induced emesis in the piglet, some animals being completely protected during both the acute and the delayed phases. [2] Granisetron (1 mg/kg, i.m.) administered three times per day reduces significantly the retching+vomiting response induced by cisplatin on days 1 and 2 by 100.0% and 75.0%, respectively, in cats. [3] Granisetron or dexamethasone significantly improves macroscopic and histologic scores, curtails myeloperoxidase activity and diminishes colonic levels of inflammatory cytokines and malondialdehyde in rats. [4] Granisetron, not only prevents cholera toxin-induced jejunal net fluid secretion but also, and in proportion, inhibits 5-HT release into the intestinal lumen of mice. [5]