What is topiramate?

Topiramate (Topamax®, Janssen Pharmaceuticals, Inc., Titusville, New Jersey) was originally approved in 1996 as a migraine-preventative treatment and seizure medication. Weight loss was initially seen as a side effect and it has now been studied directly for use in weight loss and in binge-eating disorder.

The mechanism of action of topiramate is not entirely known. One mechanism that may contribute to its weight loss effects is its effect on taste. Many patients taking this drug report certain foods taste different, especially diet colas. With altered taste sensations, some of the reward from eating certain foods may be altered. 

What is phentermine?

Phentermine was initially approved as a weight-loss drug in 1959. Phentermine is considered a stimulant-type appetite suppressant. Its major site of action is centrally in the brain. It effectively decreases hunger and gently increases metabolism. Phentermine has been studied numerous times for weight loss (in combination with diet and behavioral modification), as well as in the maintenance of weight loss.

It is now estimated that 2 of every 3 people are overweight, and about 30% of the population is obese. The studies that looked at Qnexa showed 9.8-14.7% weight loss, depending on the dose and the amount that you are overweight. A 10% weight loss is enough to improve many weight-related diseases such as pre-diabetes, high blood pressure, high cholesterol and sleep apnea. 

The Scottsdale Weight Loss Center has done researches on the effect of these two drugs.They were using both phentermine and topiramate for weight-loss – but individually. Their side effects are quite different so that some patients did better on one drug and some did better on the other.

if a patient had migraines, you should choose topiramate. If they were free of heart disease, you should choose phentermine. Now, as their experience with the combination has grown, the researchers commonly start with one drug, more often it is phentermine. For some, the phentermine’s effect is incomplete and adding topiramate has really helped.

Like all drug therapies, patients respond differently to the same drug. For a small few, their hunger is so little that the researchers have to decrease the dose so that they actually eat regularly. For most, adding the second drug boosts the appetite-suppressant effect and there is less hunger. In a small percentage, the second drug does not seem to add much or the side effects are too much, and researchers go back to a single drug therapy. In their practice, they always use medications in combination with dietary change, exercise, a behavior-based class series, accountability, and adequate sleep counseling.  

Summary

Qnexa, the first new weight-loss drug since 1999, is long overdue. It will be a good tool in the treatment of obesity. Combination drugs have been shown to improve compliance in taking all doses of a drug as prescribed. Although both phentermine and topiramate will remain available on their own in generic forms, Qnexa will be the strongest combination drug available to treat obesity and being overweight. Finally, it is important to remember that Qnexa is just one of many tools for weight loss. Its best effects will be seen as part of a complete program for weight loss that includes diet, exercise, behavior change, and adequate sleep.

By Craig Primack MD, FAAP Obesity Medicine Specialist Co-director, Scottsdale Weight Loss Center Posted on 4/18/2012 | By Craig Primack MD, FAAP