Stiripentol vs. Fenfluramine – a quick comparison of how each drug fights “refractory” seizures
| Feature | Stiripentol | Fenfluramine |
|---------|-------------|--------------|
| Primary target | GABA‑A receptor – enhances chloride influx (positive allosteric modulator). | Serotonin system – releases serotonin, acts as an agonist at 5‑HT2A/2C receptors (and modulates other serotonin‑related pathways). |
| Mechanistic core | • Boosts inhibitory tone – increases GABA availability and prolongs GABA‑mediated currents.
• Metabolism modulation – inhibits CYP2C19/CYP3A4, raising plasma levels of co‑administered AEDs (e.g., clobazam, valproate). | • Elevates serotonergic activity – serotonin release, receptor activation, and downstream signaling that dampen seizure networks.
• Indirect GABA effect – some pre‑clinical data suggest fenfluramine can modestly enhance GABAergic transmission, but this is secondary. |
| Typical clinical use | Combination therapy in Dravet syndrome (often with clobazam & valproate). | Add‑on therapy in Dravet syndrome and, increasingly, in Lennox‑Gastaut syndrome. |
| Key interactions | Very significant – can raise levels of clobazam, clobazam‑N‑hydroxyl derivative, valproate, and carbamazepine. | Minimal – few CYP interactions; mainly affects serotonergic pathways. |
| Side‑effect profile | CNS: drowsiness, dizziness; metabolic: weight gain, hypertrichosis. | Cardiac: valvulopathy (rare with low doses used for epilepsy); CNS: nausea, constipation. |
| Evidence base | Large, prospective open‑label studies (e.g., Dravet trials) show >50 % reduction in convulsive seizures. | Randomised controlled trial (RCT) in Dravet (N= 300+) showed 70 % median seizure‑frequency reduction. |
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What drives their different effects?
1. Stiripentol – a “GABA‑boosting” agent
- Pharmacology: Binds to the GABA‑A receptor complex at distinct sites, potentiating the inhibitory chloride current. This is the classic mechanism of many benzodiazepines and barbiturates, but stiripentol has a unique binding profile that is not fully understood.
- Why it works in refractory seizures: The Dravet syndrome brain has a pronounced deficiency in inhibitory tone; by strengthening GABA‑mediated inhibition, stiripentol helps tip the balance back toward stability.
- Metabolic twist: It blocks CYP enzymes, so the drug does not act only directly—it also indirectly raises the levels of other AEDs, giving a dual hit on the epileptic circuitry.
2. Fenfluramine – a “serotonin‑based” anticonvulsant
- Pharmacology: Originally a weight‑loss drug, fenfluramine releases serotonin from presynaptic terminals and activates 5‑HT2A/2C receptors. In epilepsy, the key action appears to be the serotonin‑mediated modulation of cortical excitability rather than GABA.
- Why it works in refractory seizures: Serotonin is a powerful modulator of cortical networks. By boosting serotonergic tone, fenfluramine dampens hyper‑excitable pathways that drive Dravet and Lennox‑Gastaut seizures.
- Secondary GABA link: Some preclinical studies suggest that serotonin receptor activation can indirectly influence GABA release or receptor sensitivity, but this is a secondary mechanism, not the primary driver.
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Bottom line
- Stiripentol = direct GABA‑A potentiation + metabolic amplification of other AEDs.
- Fenfluramine = enhancement of serotonin release and receptor activation (with a modest, indirect GABA effect).
Because their primary targets differ, they can be complementary in a treatment regimen: stiripentol bolsters the inhibitory system, while fenfluramine shifts the broader serotonergic tone to stabilize seizure networks. That’s why both are approved as add‑ons in Dravet syndrome, each providing a distinct mechanistic edge.