Pharmacotherapy for Pediatric Obesity: A Phentermine Clinical Trial

Obesity in children and adolescents (body mass index [BMI] ≥95th percentile) is a chronic, progressive, and debilitating disease with a prevalence of >20% in the U.S.1 Cardiovascular (CV) complications of obesity in this population are common,2 with nearly 40% of youth having ≥2 CV risk factors. Moreover, obesity in youth increases the risk of CV mortality in adulthood by nearly 5-fold. Treatment of obesity in adolescents includes lifestyle therapy (LST), and when this is ineffective, adjunct pharmacotherapy is recommended.5 However, there are few pharmacological options for pediatric obesity, and none are utilized to any significant degree by primary care pediatricians, even though obesity is the most common chronic disease of childhood.

Currently, orlistat is the only medication approved by the U.S. Food and Drug Administration (FDA) for the treatment of obesity in youth ages ≥12 years. However, adoption of orlistat in the clinical setting has been hampered by its significant side effects and poor accessibility due to high cost and poor insurance coverage. Two additional anti-obesity medications, liraglutide and combination phentermine-topiramate, are in the FDA approval pipeline for pediatric obesity, yet these are also unlikely to be widely prescribed by primary care pediatricians. Both of these medications are also expensive and are unlikely to be covered by many insurance plans. Furthermore, liraglutide is delivered by injection and topiramate has associated cognitive side effects. The paucity of safe, effective, and accessible pharmacological options has spurred pediatric obesity specialists to improvise by utilizing medications in an "off-label" manner, resorting to extrapolation of safety and efficacy data from adult clinical trials and opting for medications that are either covered by insurance or are inexpensive. One of the most commonly used medications prescribed in an "off-label" manner is phentermine.

Phentermine, a sympathomimetic, was FDA approved for obesity in 1959, before obesity was considered a chronic disease and when standards for clinical trials were lower than today. Accordingly, it was approved for short-term use, often interpreted as ≤12 weeks, in people ages >16 years. The popularity of phentermine among pediatric obesity specialists is likely driven by its demonstrated safety and efficacy in adults (4-5% mean placebo-subtracted weight loss over 26-28 weeks), oral route of administration, and affordability. Yet in spite of its popularity and routine use beyond 12 weeks, significant gaps exist in our knowledge regarding its safety and efficacy in children and adolescents, many of whom may have abnormal CV profiles at baseline. Indeed, pediatric data regarding phentermine use are sparse: only one retrospective clinical report (published by our group), demonstrated a 4% BMI reduction at 6 months with no significant increase in blood pressure.

To address these important gaps and generate evidence to directly inform clinical care, we propose this multi-site, randomized, placebo-controlled clinical trial to examine the weight loss efficacy and CV safety of phentermine 15 mg daily plus LST vs. placebo plus LST among 200 adolescents ages ≥10 to <18 years with obesity. To maximize the overall impact and clinical scalability, our explicit goal will be to generate the data necessary to support an FDA label change for phentermine to include a pediatric indication (down to age 10 years) and remove restrictions on the duration of use, thereby setting the stage for utilization in the primary care setting.