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DRUGS FOR WEIGHT LOSS: SIBUTRAMINE
Sibutramine was developed in the UK as a centrally acting, serotonin and noradrenaline reuptake inhibitor. Weight loss is facilitated by two actions:
- Sibutramine's central action on neurotransmitters causes an enhancement of satiety (fullness) after eating, which results in a 20% reduction in overall calorific intake. It is not an appetite suppressant, loss of appetite being a listed side-effect occurring in less than 10% of patients prescribed sibutramine. Prolonged satiety does, however reduce the need for snacking between meals.
- A second action is by sympathetically mediated thermogenesis, which prevents the reduction in basal metabolic rate (BMR) normally seen in individuals on restrictive diets and thereby effectively increases resting energy consumption and promotes weight loss. By virtue of its mode of action, it can cause some sympathetic stimulation and lead to unwanted cardiovascular changes.
Sibutramine is taken as a 10-mg capsule, once daily, usually in the morning. The dose can be increased to 15 mg daily after 1 month if there is insufficient weight loss (<2 kg), i.e. the patient is a 'poor responder'.
The potential side-effects of sibutramine are easily understood from its mode of action. The most common side-effects, affecting about 10% of patients, are headache, dizziness, sweating, palpitations, constipation and dry mouth. There is an average rise in diastolic blood pressure of 2.3 mmHg, the average pulse rate rising by 3 beats per minute. A significant rise in pulse rate and blood pressure can be seen in some patients, usually in the first 3 months, requiring cessation of treatment. It is therefore necessary that patients are monitored closely for cardiovascular changes, particularly in the first 3 months of treatment.
Sibutramine should not be used in patients with a proven history of coronary heart disease, cardiac arrhythmias or uncontrolled hypertension. It should also be avoided in patients who have a history of stroke, heart failure, eating disorders or psychiatric illness and in those currently treated with antipsychotics or antidepressants.
In early 2002, some concern was raised over the safety of sibutramine after the unexplained deaths of two patients in Italy. However, the European Committee for Proprietary Medicinal Products (CPMP) investigated sibutramine and concluded that it exhibits a positive favourable risk profile for the management of obesity.
Sibutramine can be used safely in well-controlled hypertensives (BP not greater than 145/90 mmHg) and in all patients blood pressure and pulse should be monitored every 2 weeks for the first 3 months of treatment, every 4 weeks for the following 3 months, and every 3 months thereafter. Treatment should be stopped if blood pressure rises by 10 mmHg on two consecutive readings or if the pulse rate rises by 10 beats per minute.
Data published by Abbott Laboratories Ltd suggest that blood pressure rises sufficiently to cause cessation of treatment in 10% of cases. Post-marketing surveillance studies from Austria have found that only 2% were sufficiently affected to require cessation of treatment on these grounds.
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WEIGHT LOSS/BODY-BUILDING
