How Stiripentol Reduces Seizures in Dravet Syndrome
Stiripentol works primarily as an allosteric modulator of GABAA receptors, boosting inhibitory signaling in the brain to suppress seizure activity. It also inhibits CYP450 enzymes (like CYP2C19 and CYP3A4), which increases levels of clobazam—a common add-on therapy in Dravet—amplifying its antiseizure effects indirectly. In clinical trials like the STICLO study, add-on stiripentol reduced monthly convulsive seizure frequency by over 50% in 71% of Dravet patients aged 1-30, compared to 42% on placebo.[1] It targets generalized tonic-clonic and myoclonic seizures effectively but shows limited impact on atypical absences.
How Fenfluramine Reduces Seizures in Dravet Syndrome
Fenfluramine acts through multiple pathways: it releases serotonin to activate inhibitory 5-HT1 receptors, modulates sigma-1 receptors for neuroprotection, and inhibits persistent sodium currents in neurons. Approved as an add-on therapy, pivotal trials (e.g., Zephyr and Study 3) showed 0.4 mg/kg/day fenfluramine cutting monthly drop seizures by 54-63% versus 20-39% for placebo in children aged 2-18.[2] It excels against drop seizures and tonic-clonic events, with broader efficacy across seizure types than stiripentol.
Key Differences in Mechanisms and Efficacy
| Aspect | Stiripentol | Fenfluramine |
|--------|-------------|--------------|
| Primary Mechanism | GABAA enhancement + CYP inhibition (boosts clobazam) | Serotonin release + sigma-1/sodium channel modulation |
| Best for Seizure Types | Tonic-clonic, myoclonic (pairs with clobazam/ valproate) | Drop seizures, tonic-clonic (monotherapy potential emerging) |
| Responder Rate (≥50% reduction) | 71% (STICLO, with clobazam)[1] | 54-74% (Zephyr/Study 3)[2] |
| Dependency | Relies heavily on clobazam co-therapy | Independent; can combine with stiripentol or cannabidiol |
| Onset and Duration | Slower buildup due to enzyme effects; sustained with chronic use | Faster onset (weeks); effects maintain over 1+ years |
Stiripentol's edge lies in synergy with clobazam for motor seizures, but it lacks standalone approval and performs poorly without it. Fenfluramine offers more consistent drop seizure control and flexibility in combinations, though its amphetamine-like history prompted cardiac monitoring requirements.[3]
Direct Comparison in Head-to-Head Data
No large randomized trials directly compare them, but real-world studies (e.g., French cohort analysis) show similar overall seizure reductions (40-60%) when both are added to stiripentol-clobazam baselines. Fenfluramine edges out in refractory drop seizures, while stiripentol better preserves clobazam responders. Combo use (fenfluramine + stiripentol) yields up to 80% response rates in some patients.[4]
Side Effects and Safety Profiles
Stiripentol commonly causes sedation, appetite loss, and tremor (20-30% incidence), worsened by CYP effects raising clobazam levels. Fenfluramine risks weight loss, diarrhea, and rare cardiac valve issues (monitored via echocardiograms), but less sedation. Long-term data favor fenfluramine for tolerability in extended trials up to 3 years.[2][3]
When to Choose One Over the Other
Clinicians pick stiripentol first for clobazam users with prominent tonic-clonic seizures; fenfluramine suits drop-heavy cases or clobazam intolerance. Cost and access vary: stiripentol (Diacomit) runs $100K+/year without insurance; fenfluramine (Fintepla) similar but with patient assistance. Patents expire around 2027-2030.5
[1]: https://pubmed.ncbi.nlm.nih.gov/23072775/
[2]: https://pubmed.ncbi.nlm.nih.gov/31141271/
[3]: https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-new-add-on-treatment-seizures-dravet-syndrome
[4]: https://pubmed.ncbi.nlm.nih.gov/34766447/