Fenfluramine is an amphetamine derivative that was withdrawn from the market worldwide in the 1990s due to the fatal cardiovascular adverse effects it caused when used as an appetite suppressant. It was recently authorised in the European Union for patients aged 2 years or older with Dravet syndrome (severe myoclonic epilepsy of infancy). This rare but severe form of epilepsy, usually of genetic origin, presents before the age of 2 years, mainly as convulsive seizures, often triggered by fever, that become increasingly frequent. The seizures are particularly serious when they last longer than 30 minutes, potentially leaving neurological sequelae or even resulting in death. About one in 6 affected children die before the age of 10 years. Treatment with antiepileptic drugs reduces the number of seizures, without preventing them entirely.

Fenfluramine (Fintepla°) was evaluated in two trials, conducted for 14 and 15 weeks, each of which included about 200 patients, in which fenfluramine or placebo was added to an antiepileptic treatment that had been deemed insufficiently effective. Adding fenfluramine reduced the frequency of convulsive seizures, when seizures of any severity were taken into account. But the incidence of the most serious seizures (convulsive status epilepticus) increased, with an additional 10% to 15% of patients experiencing such seizures. Moreover, it would be impossible to measure the impact of serious convulsive seizures on the children’s psychomotor development in such short-term trials.

In practice, given its neuropsychiatric risks, its serious cardiac risks, the risk of addiction, the excess of unexplained deaths in the group of children exposed to fenfluramine, the risk of overdose, mainly due to the drug’s unsuitable packaging, and the high risk of drug interactions, fenfluramine is not an acceptable option.

©Prescrire 1 January 2022

Source: "Fenfluramine (Fintepla°) in Dravet syndrome. Higher incidence of convulsive status epilepticus, and serious cardiovascular risks in the long term" Prescrire International 2022; 31 (233): 9-11. Subscribers only.

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