XENICAL is a potent, specific and long acting inhibitor of gastrointestinal lipases. It exerts its therapeutic activity in the lumen of the stomach and small intestine by forming a covalent bond with the active serine site of the gastric and pancreatic lipases. The inactivated enzyme is thus unable to hydrolyse dietary fat, in the form of triglycerides, into absorbable free fatty acids and monoglycerides. As undigested triglycerides are not absorbed, the resulting caloric deficit has a positive effect on weight control. Systemic absorption is therefore not needed for activity.

Single and repeated dose toxicity studies in rodents and dogs have demonstrated a similar pattern of dose related effects across species, none of which is considered relevant to the recommended use in man.

No orlistat associated mutagenicity or genotoxicity has been observed in a standard battery of five different short-term assays.

Carcinogenicity studies in rats and mice have not shown a carcinogenic potential for orlistat at doses up to 1000mg/kg/day and 1500mg/kg/day respectively. These doses are 182 and 125 times the daily human dose calculated on a body surface area (mg/m 2) basis. There was a decreased incidence of mammary fibroadenoma in female rats in the high dose group. No orlistat associated adverse effects were observed in Segment l, ll and Ill reproductive toxicity studies at doses ranging 62-241 times the recommended clinical dose.