Obesity drugs are used for patients who are morbidly obese andhave health problems that are likely to improve with weight loss. They’re used in combination with a weight management program that includes diet, physical activity, and behavioral modification. Drug therapy should be used to improve health rather than pro-mote cosmetic weight loss.
Drugs for obesity fall into two categories:
§ appetite suppressants (phentermine and sibutramine)
§ fat blockers (orlistat).
Sibutramine is rapidly absorbed from the intestines and rapidly distributed to most body tissues. It’s metabolized in the liver and excreted in the urine and feces. Orlistat isn’t absorbed systemical-ly; its action occurs in the GI tract. Orlistat is excreted in the feces.
Appetite suppressants increase the amount of norepinephrine and dopamine in the brain, thereby suppressing the appetite. The fat-blocking drug orlistat binds to gastric and pancreatic lipases in the GI tract, making them unavailable to break down fats. This blocks absorption of 30% of the fat ingested in a meal.
Appetite suppressants and fat blockers are used primarily for weight loss when losing weight will improve the patient’s health and prevent death.
Obesity drugs interact with other drugs.
§ Appetite suppressants taken with cardiovascular stimulants may increase the risk of hypertension and arrhythmias.
§ Appetite suppressants taken with central nervous system (CNS) stimulants can cause increased anxiety and insomnia.
§ Appetite suppressants taken with serotonergic drugs (including fluoxetine, sumatriptan, dextromethorphan, and lithium) can cause agitation, confusion, hypomania, impaired coordination, loss of consciousness, nausea, or tachycardia.
§ Orlistat blocks the absorption of fat-soluble vitamins if taken together. (See Adverse reactions to obesity drugs.)