These agents decrease food intake by reducing appetite or increasing satiety. The mechanisms of action are to increase secretion of dopamine, norepinephrine, or serotonin into the synaptic neural cleft, to inhibit the reuptake of these neurotrans-mitters into the neuron or a combination of the two effects. There are three classes of anorexiant drugs, and all affect neurotransmitters in the brain.
1. Affect catecholamines: dopamine and norepinephrine. These noradrenergic agents are useful for short term treatment and include the drugs phenteremine, diethylpropion, phendimetrazine and benzphetamine. Stimulants act via catecholamine neurotransmitters, such as amphetamines and phenylpropanolamine. Phenylpropanolamine, which was an over-the-counter medication, was removed secondary to an association with hemorrhagic stroke. Side effects of this class of medications include insomnia, dry mouth, constipation, euphoria, palpitations and hypertension.
2. Affect serotonergic: Fenfluramine and dexfenfluramine are included in this class. These medications have been associated with valvular heart disease and pulmonary hypertension. In 1997, the "Phen/fen" combination was withdrawn from the market after reports of valvopathy after as little as one month's use of this medication. The mechanism apparently involves serotonin stimulation of fibroblast growth and fibrogenesis.
3. Affect more than one neurotransmitter. Sibutramine (Meridia) is an appetite suppressant that works via norepi and serotonergic mechanisms in the brain (Fig. 6.1). Side effects include tachycardia and hypertension.
The newly discovered endocannabinoid (EC) system and cannabinoid CB1 receptor play an important role in appetite and energy regulation and offer a novel target for a new class of anti-obesity drugs. Rimonabant, the first specific CB1-receptor blocker to enter clinical development, has been shown to reduce food intake and body weight in treated animals, and there are also beneficial effects in the adipocyte. The results of phase 3 studies involving obese patients have shown that rimonabant induces significant weight loss and improves metabolic risk factors for diabetes and cardiovascular disease. It is anticipated that this drug will be available in the near future for the treatment of obesity in the U.S. Common side effects in preclinical studies included depression, anxiety, and nausea.
Certainly, close monitoring for side effects with any weight loss medication is necessary. Several randomized controlled studies of weight loss medications have been performed, but questions remain concerning long-term effects on health, the
optimal duration of treatment, and the use of combination regimens including polypharmacy and combination with lifestyle interventions.
Orlistat (Xenical) binds GI lipases in the lumen of gut, which prevents hydrolysis of dietary fat (triglycerides) into absorbable free fatty acids and monoacylglycerols (Fig. 6.2). Orlistat is an irreversible lipase inhibitor and thus decreases the amount of ingested dietary fat that is absorbed Side effects of this medication include decreased absorption of fat-soluble vitamins and nutrients, flatulence, fecal urgency and incontinence, steatorrhea, oily spotting and increased frequency of defecation.
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Make a plan If you want to lose weight, you need to make a plan for it. Planning involves setting your goals both short term and long term ones. With proper planning, you would be able to have an effective guide on the steps that you want to take, towards losing pounds of weight. Aside from that, it would also keep you motivated.