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Orlistat is a gastrointestinal lipase inhibitor indicated for obesity management, including weight loss and weight maintenance, when used in conjunction with a reduced-calorie diet. 

The first in a new class of drugs, orlistat works non-systemically to block the absorption of dietary fat. Even though orlistat was placed on a fast-track by the FDA, final approval was delayed when results of clinical trials suggested a higher incidence of breast cancer in the orlistat group compared to placebo. 

Based on orlistat's minimal systemic absorption, lack of an estrogen-stimulating effect in women, and evidence of tumor preexistence at randomization, investigators concluded that no biological association between orlistat and breast cancer exists. Orlistat was approved for use in Europe in July 1998, and the FDA granted approval for use in adults in April 1999. In December 2003 the FDA approved orlistat for use in obese adolescents 12 to 16 years of age.

Glaxo SmithKline, the manufacturer of Xenical®, filed a switch to over-the-counter (OTC) application in June 2005 for a reduced dose product. An FDA Joint Advisory Committee recommended approval in January 2006. On February 7, 2007, the FDA approved Alli™, an orlistat 60 mg capsules for OTC use.

Mechanism of Action: 

Orlistat produces weight loss through inhibition of nutrient absorption. 

A covalent bond is formed with the active serine residue site of gastric and pancreatic lipases within the lumen of the stomach and the small intestine. As these enzymes become unavailable to hydrolyze dietary triglycerides into free fatty acids and monoglycerides, less fat is absorbed by the body. 

This results in decreased caloric intake that may result in negative energy balance and weight loss. Therefore, systemic absorption of the drug is not needed to produce a weight-lowering effect. At the recommended therapeutic dose of 120 mg orlistat PO three times per day, dietary fat absorption is inhibited by approximately 30%.


Orlistat is administered orally and has minimal systemic absorption. Sporadic intact amounts of orlistat, low plasma concentration levels (<10 ng/ml), and no evidence of accumulation were observed during therapeutic studies. In vitro, orlistat was > 99% bound to plasma proteins (primarily lipoproteins and albumin) with minimal partitioning into erythrocytes. 

Metabolism of orlistat to weakly active and inactive metabolites is believed to occur mainly within the gastrointestinal wall. Approximately 83% of a single oral dose of orlistat was excreted unchanged in the feces. Renal excretion was < 2% of the dose. Complete excretion of both urinary and fecal orlistat was reached in 3 to 5 days. The estimated half-life of the absorbed portion of orlistat was approximately 1 to 2 hours.

•Route-Specific Pharmacokinetics

Oral Route

Peak plasma concentrations of orlistat (<5 ng/ml) occurred approximately 8 hours after a 360 mg dose. Based on fecal fat measurements, the effect of orlistat may be seen within 24 to 48 hours.

 Obesity is one of the most challenging disorder to treat for endocrinologists. To aggravate the situation the first line therapy till now that is sibutramine has been under scrutiny after SCOUT trial.... EUROPEAN UNION even has banned recently (blanket ban).
Orlistat was initially considered second line therapy after sibutramine, but many endocrinologist now considering orlistat as first line anti obesity therapy.
Orlistat main side effects is gastrointestinal ..... which rarely become intolerable. BUT problem is high cost of orlistat....sibutramine is much cheaper/ affordable drug.
so need for gud antiobesity drug is required at the earliest

IDLI versus VADA

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