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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.

Read more at Wikipedia.org

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Orlistat does not improve insulin sensitivity independent of weight loss - Weight Loss
From Nutrition Research Newsletter, 2/1/04

It has been shown that diet composition influences insulin sensitivity independent of body weight. Diets with a high fat content seem to impair insulin sensitivity more than high-carbohydrate, low-fat diets do. However, not all fats impact insulin sensitivity in the same way. It appears that decreasing the proportion of saturated fatty acids (SFAs) and increasing that of mono-unsaturated fatty acids (MUFAs) improves insulin sensitivity, although, the underlying mechanism is unknown. Orlistat, a weight loss medication that inhibits gastric and pancreatic lipases, has also been shown to alter the proportion of fatty acids in serum triacylglycerols. The inhibition of fat absorption with the use of orlistat has been associated with a greater improvement in insulin sensitivity than has the use of placebos.

In order to ascertain whether orlistat has weight loss-independent effects on insulin sensitivity or body composition in obese women with a history of gestational diabetes (a risk factor for developing type 2 diabetes), a double-blind, placebo-controlled study was conducted. The aim was to achieve 8% weight loss over a similar period in women taking orlistat and in those taking a placebo. Forty-seven obese women were randomly assigned to receive either orlistat (120 mg 3 times per day; n = 23) or placebo (n = 24) with a hypocaloric diet. Whole-body insulin sensitivity (insulin clamp technique), serum fatty acids, and body composition (magnetic resonance imaging) were measured before and after weight loss.

The two groups did not differ significantly at baseline in regard to age, body weight, intra-abdominal and subcutaneous fat volumes, or insulin sensitivity. Weight loss did not differ significantly between the orlistat (7.3 kg [+ or -] 0.2 kg, or 8.3% [+ or -] 0.1%) and placebo (7.4 kg [+ or -] 0.2 kg, or 8.2% [+ or -] 0.1%) groups. Insulin sensitivity improved significantly (P < 0.001) after weight loss in the orlistat (from 4.0 [+ or -] 0.3 mg x kg fat-free [mass.sup.-1] x [min.sup.-1] to 5.1 [+ or -] 0.3 mg x kg fat-free [mass.sup.-1] x [min.sup.-1]) and placebo (from 4.4 [+ or -] 0.4 mg x kg fat-free [mass.sup.-1] x [min.sup.-1] to 5.4 [+ or -] 0.4 mg x kg fat-free [mass.sup.-1] x [min.sup.-1]) groups. Intra-abdominal fat and subcutaneous fat decreased significantly in both groups, but the ratio of these two decreased significantly only in the orlistat group. The proportion of dihomo-a-linolenic acid (20:3n-6) in serum phospholipids was inversely related to insulin sensitivity both before (r=-0.48, P<0.001) and after (r = -0.46, P < 0.001) weight loss, but it did not change significantly in either group.

It appears that weight loss, rather than the inhibition of fat absorption, improves insulin sensitivity. A decrease in fat absorption caused by orlistat does appear to favorably influence the ratio between intra-abdominlal and subcutaneous fat.

M. Tiikkainen, R. Bergholm, A. Rissanen, et al. Effects of equal weight loss with orlistat and placebo on body fat and serum fatty acid composition and insulin resistance in obese women. Am. J. Clin. Nutr. 79:22-30 (January 2004) [Correspondence: H Yki-Jarvinen, Department of Medicine, University of Helsinki, P.O. Box 340, FIN-00029 HUCH, Helsinki, Finland E-mail: ykijarvi@helsinki.fi.]

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