Effect of Fenfluramine on convulsive seizures and rescue medication usage: A case series of adults within the Lennox-Gastaut syndrome spectrum

Abstract

Introduction Adults with Developmental and epileptic encephalopathies (DEE) within the Lennox-Gastaut Syndrome (LGS) spectrum suffer disabling convulsive seizures which may remain refractory and are associated with increased risk of hospitalisations and death. Fenfluramine (FFA) was licenced in the UK for seizures associated with LGS in March 2025. Methods Adjunctive FFA was assessed in a series of 6 adults with a genetic DEE within the LGS spectrum treated for refractory convulsive seizures. The minimum period of observation was 9 months (range 9–32 months). 3 patients commenced FFA pre-licencing on compassionate grounds. 4 patients had a VNS, 5 patients were prescribed concomitant Cannabidiol. Reduction in convulsive seizures and reduction in use of rescue medications/ frequency of hospitalisations was also assessed. Caregiver responses were recorded using the Clinical Global Improvement of Change (CGI—I). Results At last follow up, all 6 patients remained on FFA. No significant side effects were observed. There was a significant reduction in seizures at last follow up (p = 0.035), with a corresponding reduction in use of rescue medications and hospitalisations. On the CGI—I, 5 of the 6 patients were rated as much/ very much improved, the remaining patient was rated as minimally improved. Conclusion Adjunctive FFA was tolerated without significant side effects and associated with a significant reduction in convulsive seizures in this limited cohort. Corresponding reduction in use of rescue medications and hospitalisations has the potential to impact on both patient and caregiver quality of life.