DRUGS FOR WEIGHT LOSS: ORLISTAT
Orlistat was developed to reduce the amount of dietary fat absorbed from the small intestine and so decrease an individual's
total calorific intake. Acting locally to block the action of pancreatic and gastric lipase enzyme, it reduces absorption of fat -
in particular triglycerides - by up to one-third. The unabsorbed dietary fat is excreted through the intestine.
The average fat content of a Western diet can be as high as 45% and contributes greatly to overall calorific intake. Reducing
fat intake by dietary means can produce significant benefits. However, further reductions in dietary fat absorption can be achieved
by the addition of orlistat, thereby achieving further net decreases in energy intake and contributing to a negative energy equation
that can result in net weight loss. It is absolutely essential that the patient has been instructed in, and has adapted to, a low-fat
diet before treatment is commenced.
Orlistat is prescribed as 120-mg capsules, one of which is to be taken three times a day during (or up to one hour after) meals.
Patients must have been instructed in, and demonstrated that they can follow, a low-fat dietary regime. Failure to adhere to a low-fat
diet can result in unpleasant side-effects and will lead to poor compliance and early cessation of treatment. If a meal is missed, the
medication should be omitted. Some patients will choose to omit individual doses when eating out or when knowingly eating a high-fat meal.
Patients taking vitamin supplements should ensure they do not take them within 2 hours of taking orlistat.
Because of its local mode of action, orlistat has no common systemic side-effects. If the patient fails to adhere to a low-fat diet (less than 30%
calories taken in as fat) the inhibited intestinal absorption can lead to oily spotting, flatus, faecal urgency and anal leakage.
Patients can be helped to view these effects positively, as 'treatment effects' and learn to adapt their dietary intake accordingly.
Occasionally, malabsorption of the fat-soluble vitamins A, D, E and E might occur, although this is not a practical risk in normal clinical practice
or when a patient is limited to a prescription duration of 12 months. Some clinicians choose to prescribe vitamin supplements in those taking
orlistat for more than 1 year.
Orlistat is contraindicated in patients with cholestasis or malabsorptive syndromes. It should also not be used in patients who are unable to
tolerate or maintain a low-fat diet.
Treatment with orlistat can reduce vitamin E absorption so special attention is warranted in anticoagulated patients. Patients on warfarin therapy
should have their international normalized ratio (INR) checked regularly.
Orlistat might also reduce the absorption of cyclosporin and it is therefore advisable to monitor blood levels. Despite initial concerns, there is no
data to support the association of orlistat with breast cancer.