A review of the metabolic effects of controlled-release Phentermine/Topiramate

Very few drugs are approved for obesity treatment by regulatory agencies. Very recently phentermine/topiramate controlled-release [PHEN/TPM CR; (Qsymia®)] obtained Food and Drug Administration (FDA) approval as an addition to a reduced-calorie diet and exercise for chronic weight management. Our aim was to review the available clinical evidence on weight loss, metabolic effects and adverse events associated with use of this product.

Randomized controlled trials with phentermine/topiramate controlled-release were selected through a Medline search using the terms: phentermine and topiramate, phentermine and controlled release topiramate, new anti-obesity drugs and phentermine/topiramate, recent combinations of anti-obesity drugs and Qnexa®.

PHEN/TPM CR was associated with a weight loss of 8.1-10.9 % (mid and high dose, respectively), while patients in placebo groups lost 1.4-1.8 % of their initial weight. PHEN/TPM CR also resulted in a significant decrease of waist circumference. Weight loss with PHEN/TPM CR was associated with a decrease in blood pressure but with a slight increase in the heart rate. Furthermore, in all trials it exerted favorable effects on lipid profile, especially on triglycerides and high-density lipopoprotein (HDL) cholesterol. PHEN/TPM CR treatment also improved insulin sensitivity and glycemia. Moreover, it decreased significantly progression to type 2 diabetes. In all of the studies the severe adverse events were similar between the control groups and the groups of PHEN/TPM CR. The most frequent side-effects observed in the active treatment group were paresthesia, dysgeusia, dry mouth, constipation and insomnia.

PHEN/TPM CR combined with lifestyle modification may be an effective and well-tolerated treatment for obesity and weight-related metabolic complications. Its long-term efficacy and safety have yet to be defined.