A Benefit-Risk Assessment of Sibutramine in the Management of Obesity

Obesity is a multifactorial, chronic disorder that has reached epidemic proportions in most industrialised countries and is threatening to become a global epidemic. Clinical management of obese patients is complex and serious doubts have arisen with regard to safety and efficacy of drug therapy. Following the withdrawal of fenfluramine and dexfenfluramine in 1997, interest has focused on novel anti-obesity drugs. Pharmacological approaches to the management of obesity can, in broad terms, use different distinct strategies: firstly, to reduce energy intake; secondly, to increase energy expenditure; and thirdly, to alter the partitioning of nutrients between fat and lean tissue.

Sibutramine is a serotonin-noradrenaline (norepinephrine) reuptake inhibitor indicated for the management of obesity in conjunction with a reduced calorie diet. The pharmacological mechanisms by which sibutramine exerts its weight loss effect are likely due to a combination of reduced appetite, feelings of satiety and possibly the induction of thermogenesis.

The efficacy of sibutramine for inducing initial weight loss and the subsequent maintenance of weight loss is well proven in short- and long-term clinical trials of up to 2 years’ duration. Most individual placebo-controlled trials and pooled estimates found that the drug produced statistically significant greater weight loss than placebo at all observed endpoints (weighted mean difference for weight change at 8 weeks: −3.4kg; mean difference range for weight change at 6 months: −4.0 to −9.1kg; and at 1 year: −4.1 to −4.8kg). The most frequent dosage regimen in these trials was 10–20mg daily. Findings suggested a dose-effect relationship in terms of weight loss. Sibutramine was also associated with better weight maintenance relative to placebo (statistically significant difference). Results from mainly small trials showed that sibutramine produced more favourable outcomes in terms of loss of fat mass, reduction in body mass index and loss of ≥5–10% of initial bodyweight.

The most commonly reported adverse effects of sibutramine are headache, constipation and nausea. Certain adverse events associated with the nervous system, including dizziness, dry mouth and insomnia, are reported by >5% of patients receiving sibutramine. Increases in blood pressure and heart rate were possible adverse effects that require regular monitoring especially in obese hypertensive patients. Neither left-sided cardiac valve disease nor primary pulmonary hypertension was associated with the use of sibutramine. The assessment of the benefit-risk profile of sibutramine remained positive, although the product must be kept under regular review.