Initial weight loss as a predictor of response to obesity drugs

BACKGROUND: Initial weight loss has been used as a predictor of long-term response to obesity drugs. Discontinuation of drugs has been recommended if weight loss is not ≥ 1.81 kg (4 lb) in the first month of treatment. OBJECTIVE: We compared the weight loss response at 6 months of patients losing ≥ 1.81 kg (responders) vs < 1.81 kg (non-responders) in the first month of treatment with the combination of fenfluramine and phentermine. DESIGN: Outcomes at 6 months in 975 patients treated in a comprehensive program of phentermine (15-30 mg/d) d,l-fenfluramine (20-60 mg/d), were compared for responders vs non-responders. RESULTS: In the total population, first month weight loss highly correlated with % reduction in body mass index (BMI) after 6 months of treatment (P < 0.001). The reduction in baseline BMI after 6 months treatment was greater for the responders (15.9% vs 10%, P < 0.02). However, the North American Association for the Study of Obesity (NAASO) guidelines for drug treatment of obesity state that a 5% weight loss produces significant health benefits, and may be used as a criteria for success. At 6 months, 76%, 37% and 14% of the non-respondents had lost ≥ 5%, ≥ 10% and ≥ 15% of baseline BMI, respectively. After 6 months treatment the reductions in serum cholesterol, triglycerides and LDL-cholesterol were 0.55, 0.31 and 0.42 mmol/L, respectively, (P ≤ 0.006), for the non-responders. Adverse effects after 6 months of treatment and the dropout rates after 1 y of treatment were not significantly different for the two groups. CONCLUSIONS: Although, the first month weight loss predicted the long-term response to phen-fen treatment, it was inadequate in identifying the non-responders and may unnecessarily preclude potential beneficiaries of the treatment.