This is a report on results from an open-label extension study of fenfluramine in children and young adults (2–18 years old) with Dravet syndrome. “Open-label extension” means that the participants have participated in the Phase 3 clinical trial and are continuing with the drug, but can know information that was previously blinded, such as the amount they are taking, and they will know they are not receiving a placebo.

A total of 232 patients were studied –  55.2% were male, and the mean age was 9.1 years. Median duration of treatment was 256 days (the range was 58–634 days). Treatment was discontinued by 22 patients (16 due to lack of efficacy). Over the entire observation period, 64.4% of patients demonstrated a 50% reduction in convulsive seizure frequency, and 41.2% demonstrated a 75% reduction. At 12 months. 70.4% of caregivers and 77.8% of investigators rated patients as “much improved” or “very much improved.”

Side-effects were not overly severe. Given that fenfluramine was once a diet drug, it is of interest that 15.9% experienced decreased appetite.  Of more importance, given that higher-dose fenfluramine was withdrawn from the market due to cardiac liabilities, no patient had any echocardiographic or clinical signs of valvular heart disease or pulmonary hypertension at any time during the study. The most common finding was intermittent and transient physiologic/trace valve regurgitation, a finding seen in normal healthy children and young adults.

Pringsheim, M. et al. Fenfluramine HCl (Fintepla®) Provides Long-Term Clinically Meaningful Reduction in Seizure Frequency: Results of an Open-Label Extension Study. Neuropediatrics 2019; 50(S 02): S1-S55. doi: 10.1055/s-0039-1698219.