General Information

Qsymia is a combination of phentermine, a sympathomimetic amine anorectic, and topiramate extended-release, an antiepileptic drug.

Qsymia is specifically indicated as an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in adult patients with an initial body mass index (BMI) of 30 kg/m2 or greater (obese), or 27 kg/m2 or greater (overweight) in the presence of at least one weight related comorbidity such as hypertension, type 2 diabetes mellitus, or dyslipidemia. Also improved for pediatric patients aged 12 years and older with BMI in the 95th percentile or greater standardized for age and sex.

Qsymia is supplied as a tablet for oral administration. Qsymia should be administered once daily in the morning with or without food. Avoid dosing with Qsymia in the evening due to the possibility of insomnia.

The recommended dose is as follows:

• Start treatment with Qsymia 3.75 mg/23 mg (phentermine/topiramate extended-release) daily for 14 days; after 14 days increase to the recommended dose of Qsymia 7.5 mg/46 mg once daily.
• Evaluate weight loss after 12 weeks of treatment with Qsymia 7.5 mg/46 mg. If at least 3% of baseline body weight has not been lost on Qsymia 7.5 mg/46 mg, discontinue Qsymia or escalate the dose.

To escalate the dose:

• Increase to Qsymia 11.25 mg/69 mg daily for 14 days; followed by dosing Qsymia 15 mg/92 mg daily.
• Evaluate weight loss following dose escalation to Qsymia 15 mg/92 mg after an additional 12 weeks of treatment. If at least 5% of baseline body weight has not been lost on Qsymia 15 mg/92 mg, discontinue Qsymia as directed.

Side Effects

Adverse events associated with the use of Qsymia may include, but are not limited to, the following:

• paraesthesia
• dizziness
• dysgeusia
• insomnia
• constipation
• dry mouth

Mechanism of Action

Qsymia is a combination of phentermine, a sympathomimetic amine anorectic, and topiramate extended-release, an antiepileptic drug. Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, amphetamine. The effect of phentermine on chronic weight management is likely mediated by release of catecholamines in the hypothalamus, resulting in reduced appetite and decreased food consumption, but other metabolic effects may also be involved. The exact mechanism of action is not known. The precise mechanism of action of topiramate on chronic weight management is not known. Topiramate’s effect on chronic weight management may be due to its effects on both appetite suppression and satiety enhancement, induced by a combination of pharmacologic effects including augmenting the activity of the neurotransmitter gamma-aminobutyrate, modulation of voltage-gated ion channels, inhibition of AMPA/kainite excitatory glutamate receptors, or inhibition of carbonic anhydrase.

Clinical Trial Results

The FDA approval of Qsymia was based on two randomized, double-blind, placebo controlled studies in obese patients (Study 1) and in obese and overweight patients with two or more significant co-morbidities (Study 2). Both studies had a four-week titration period, followed by 52 weeks of treatment. Two co-primary efficacy outcomes were measured after 1 year of treatment (Week 56): 1) the percent weight loss from baseline; and 2) treatment response defined as achieving at least 5% weight loss from baseline. During the studies, a well-balanced, reduced-calorie diet to result in an approximate 500 kcal/day decrease in caloric intake was recommended and subjects were offered nutritional and lifestyle modification counseling.
Study One
Obese subjects (BMI greater than or equal to 35 kg/m2) were randomized to receive 1 year of treatment with placebo (N=514), Qsymia 3.75 mg/23 mg (N=241), or Qsymia 15 mg/92 mg (N=512). At the beginning of the study the average weight and BMI was 116 kg and 42 kg/m2, respectively. In this study 40% of randomized subjects withdrew prior to week 56. After 1 year of treatment with Qsymia, all dose levels resulted in statistically significant weight loss compared to placebo. A statistically significant greater proportion of the subjects randomized to Qsymia than placebo achieved 5% and 10% weight loss: 17%, 45% and 67% and 7%, 19% and 47% in the placebo, Qsymia 3.75 mg/23 mg and Qsymia 15 mg/92 mg arms, respectively.
Study Two
Overweight and obese subjects were randomized to receive 1 year of treatment with placebo (N=994), Qsymia 7.5 mg/46 mg (N=498), or Qsymia 15 mg/92 mg (N=995). Eligible subjects had to have a BMI greater than or equal to 27 kg/m2 and less than or equal to45 kg/m2 (no lower limit on BMI for patients with type 2 diabetes) and two or more of the following obesity-related co-morbid conditions: elevated blood pressure, triglycerides greater than 200-400 mg/dL, elevated fasting blood glucose or diabetes and waist circumference greater than or equal to 102 cm for men or greater than or equal to 88 cm for women. The average weight and BMI at the start of the study was 103 kg and 36.6 kg/m2, respectively. In this study 31% of randomized subjects withdrew prior to week 56. After 1 year of treatment with Qsymia, all dose levels resulted in statistically significant weight loss compared to placebo. A statistically significant greater proportion of the subjects randomized to Qsymia than placebo achieved 5% and 10% weight loss: 21%, 62% and 70% and 7%, 37% and 48% in the placebo, Qsymia 7.5 mg/46 mg and Qsymia 15 mg/92 mg treatment arms, respectively.