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Orlistat

Orlistat (marketed as Xenical by Roche) is a drug designed to treat obesity. Its primary function is to prevent the absorption of dietary fats, thereby reducing caloric intake. It is intended for use in conjunction with a physician-supervised reduced calorie diet. more...

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Pharmacology

Orlistat works by inhibiting pancreatic lipase, an enzyme that breaks down triglycerides in the intestine. Without this enzyme, triglycerides from the diet are prevented from being hydrolyzed into absorbable free fatty acids and are excreted undigested. Only trace amounts of orlistat are absorbed systemically, the primary effect is local lipase inhibition within the GI tract after an oral dose. The primary route of elimination is through the feces.

At the standard prescription dose of 120 mg three times daily before meals, orlistat prevents approximately 30% of dietary fat from being absorbed.

Efficacy

The amount of weight loss achieved with orlistat is variable. In 1 year clinical trials, between 35.5% and 54.8% of subjects achieved a 5% or greater decrease in body mass. Between 16.4% and 24.8% achieved at least a 10% decrease in body mass. A significant amount of subjects regained the weight after they stopped using orlistat. Despite this cosmetically small effect, there was a 37% reduction in the incidence of Type 2 diabetes, a significant difference.

Side effects

The primary side effects of the drug are GI-related. Side effects were most severe within the first year of therapy. Because its main effect is to prevent dietary fat from being absorbed, the fat is excreted unchanged in the feces and so the stool may become oily or loose. Increased flatulence is also common. Bowel movements may become frequent or urgent. Rare occurrence of fecal incontinence have been seen in clinical trials. To minimize these effects, foods with high fat content should be avoided.

The absorption of fat-soluble vitamins are inhibited by the use of orlistat. A multivitamin tablet containing these vitamins (D, E, A and beta-carotene) should be taken once a day, at least 2 hours before or after taking the drug.

Contraindications

Xenical is contraindicated in:

Malabsorption
Reduced gallbladder function (e.g. after cholecystectomy)
Pregnancy and breastfeeding
Certain kidney problems

Availability

In most areas orlistat is available by prescription only. In 2004, a lower-dose version of the drug (60 mg compared to 120 mg for the prescription version) was released over the counter in Australia and New Zealand; the United States is expected to follow in the near future.

On January 23, 2006, a US Food and Drug Administration advisory panel voted 11 to 3 to recommend the approval of an OTC formulation of orlistat (planned to be marketed under the name "Alli" by GlaxoSmithKline). The proposed product will consist of 60 mg dosage units, similar to the OTC products available elsewhere.

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Orlistat may help in treatment of PCOS, small study shows
From OB/GYN News, 3/1/05 by Christine Kilgore

The weight loss drug orlistat may prove to be a useful adjunct in the treatment of polycystic ovarian syndrome, according to findings from a small randomized study that compared the drug with metformin.

"[We've] demonstrated the therapeutic potential of orlistat in PCOS," said Vijay Jayagopal, M.D., of the University of Hull (England) and his associates.

After a 12-week treatment period, 10 women treated with orlistat lost significantly more weight than 11 patients treated with metformin (a 4.7% vs. a 1% reduction) and had similar, statistically significant reductions in total serum testosterone (J. Clin. Endocrinol. Metab. 2005;90:729-33).

Neither drug produced significant reductions in fasting insulin, insulin resistance, sex hormone-binding globulin, or any of several lipid parameters studied.

In a written statement, Andrea E. Dunaif, M.D., president-elect of the Endocrine Society, said further research is needed to determine "where [weight-loss medications] will fit into the treatment of PCOS."

The current study, however, "suggests that [the] medications may be an effective treatment option for not only the obesity but also the testosterone excess associated with PCOS," said Dr. Dunaif of Northwestern University, Chicago.

Before drug treatment, all 21 patients--white women with PCOS--underwent an 8-week period of dietary modification (there were no significant changes in weight); they were then randomized to receive orlistat, which inhibits triglyceride and lipid absorption, or the insulin-sensitizing agent metformin.

Compared with baseline, a significant reduction in serum testosterone was observed after treatment in both the orlistat-treated group (approximately 94 ng/dL vs. 115 ng/dL) and the metformin-treated group (approximately 97 ng/dlL vs. 120 ng/dL).

Investigators noted that despite the lack of statistically significant improvements in many of the endocrine and metabolic parameters studied, the percentage changes from baseline were "more marked" in the orlistat group.

This may suggest that "the weight reduction had an overall stronger impact on these parameters than the insulin-sensitizing effect of metformin, the mechanism of which remains largely unknown," they said.

Insulin resistance was calculated using the homeostasis model of assessment (HOMA-IR) method. The lack of statistically significant improvement in insulin resistance may be due in part to the large variability in HOMA-IR values in such a small group of patients, Dr. Jayagopal and his associates said.

The investigators did not collect information on menstrual change and ovulation, and the study was not powered to assess lipid changes. Such information is "clearly important" to acquire in larger studies, the investigators said.

In the meantime, Dr. Dunaif said, "we know that metformin is a proven and effective treatment for women with polycystic ovary syndrome."

BY CHRISTINE KILGORE

Contributing Author

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