AbstractObjectiveTo assess efficacy and tolerability of stiripentol (STP) as adjunctive treatment in Dravet syndrome and non‐Dravet refractory developmental and epileptic encephalopathies (DREEs).MethodsRetrospective observational study of all children and adults with DREE and prescribed adjunctive STP at Hospital Ruber Internacional from January 2000 to February 2023. Outcomes were retention rate, responder rate (proportion of patients with ≥50% reduction in total seizure frequency relative to baseline), seizure freedom rate, responder rate for status epilepticus, rate of adverse event and individual adverse events, reported at 3, 6, and 12 months and at final visit. Seizure outcomes are reported overall, and for Dravet and non‐Dravet subgroups.ResultsA total of 82 patients (55 Dravet syndrome and 27 non‐Dravet DREE) were included. Median age was 5 years (range 1–59 years), and median age of epilepsy onset was younger in the Dravet group (4.9 [3.6–6] months) than non‐Dravet (17.9 [6–42.3], P < 0.001). Median follow‐up time STP was 24.1 months (2 years; range 0.3–164 months) and was longer in the Dravet group (35.9 months; range 0.8–164) than non‐Dravet (17 months range 0.3–62.3, P < 0.001). At 12 months, retention rate, responder rate and seizure free rate was 68.3% (56/82), 65% [48–77%] and 18% [5.7–29%], respectively. There were no statistically significant differences between groups on these seizure outcomes. Adverse events were reported in 46.3% of patients (38/82), without differences between groups.SignificanceIn this population of patients with epileptic and developmental encephalopathies, outcomes with adjunctive STP were similar in patients with non‐Dravet DREE to patients with Dravet syndrome.