Fenfluramine Stats & Data
CCNC(C)Cc1cccc(c1)C(F)(F)FDBGIVFWFUFKIQN-UHFFFAOYSA-NPharmacology
DrugBankDescription
Dravet syndrome is a pediatric encephalopathy that typically manifests within the first year of life following exposure to elevated temperatures. It is characterized by recurrent pharmacoresistant seizures, which increase in frequency and severity with disease progression. Concomitantly with these seizures, patients typically display delayed development and neurocognitive impairment. Fenfluramine is a serotonergic phenethylamine originally used as an appetite suppressant until concerns regarding cardiotoxicity in obese patients lead to its withdrawal from the market in 1997. Through its ability to modulate neurotransmission, fenfluramine has reemerged as an effective therapy against pharmacoresistant seizures, such as those involved in Dravet syndrome. Fenfluramine was granted initial FDA approval in 1973 prior to its withdrawal; it was granted a new FDA approval on June 25, 2020, for treatment of Dravet syndrome patients through the restricted FINTEPLA REMS program. It is currently sold under the name FINTEPLA® by Zogenix INC.
Mechanism of Action
Dravet syndrome is a complex pediatric encephalopathy characterized by recurrent pharmacoresistant seizures of variable type, delayed development, and in many cases, impairment in speech, language, gait, and other neurocognitive functions. Despite substantial variation in presentation and severity, roughly 80% of patients with Dravet syndrome have mutations in the _SCN1A_ gene, which encodes the alpha subunit of a voltage-gated sodium channel (Nav1.1). This channel is predominantly localized in inhibitory GABAergic interneurons as well as in excitatory pyramidal neurons; it is thought that dysfunction of neurotransmission regulation results in the seizures and other corresponding symptoms of Dravet syndrome. Various _in vitro_ and _in vivo_ studies have demonstrated that fenfluramine is capable of acting as an agonist of multiple serotonin receptors including 5-HT1A, 5-HT1D, 5-HT2A, 5-HT2B, and 5-HT2C, as well as a σ1 receptor antagonist. This is at least partly because fenfluramine, as well as its active metabolite norfenfluramine, can act on sodium-dependent serotonin transporters (SERTs) to reverse transport direction and thereby increase extracellular serotonin levels.
Pharmacodynamics
Fenfluramine increases extracellular serotonin levels, and also acts as both a serotonergic 5-HT2 receptor agonist and σ1 receptor antagonist. These activities, through an incompletely understood mechanism, lead to anti-epileptiform activity and therapeutic benefit. This modulation has other effects such as decreased appetite, weight loss, sedation, lethargy, increased blood pressure, and mood alteration including possible suicidal ideation. There is a risk of glaucoma and potentially fatal serotonin syndrome. Fenfluramine should be gradually withdrawn following treatment alteration or cessation.
Metabolism
Fenfluramine is metabolized primarily in the liver by CYP1A2, CYP2B6, CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 to yield the major active metabolite norfenfluramine and several other minor inactive metabolites.
Absorption
Fenfluramine has a steady-state Tmax of between four and five hours and an absolute bioavailability of approximately 68-74%. Fenfluramine administered to pediatric patients at 0.7 mg/kg/day up to 26 mg resulted in a mean Cmax of 68.0 ng/mL with a coefficient of variation of 41%; similarly the AUC0-24 was 1390 (44%) ng\*h/mL.
Toxicity
Overdosage of fenfluramine has been reported; in overdose cases, symptoms include agitation, anxiety, restlessness, twitching, tremors/muscle spasms, flushing, tachycardia, mydriasis, increased muscle tone, respiratory distress/failure, seizure, and coma. Some overdosage cases proved fatal, and in most fatal cases, patients experienced seizures, coma, and cardiorespiratory arrest. There is currently no standard practice for managing fenfluramine overdose. Symptomatic management, including ensuring proper ventilation and monitoring of both cardiac and respiratory functions is recommended.
Indication
Fenfluramine is indicated for the treatment of seizures in Dravet syndrome patients aged two years and older.
Half-life
Fenfluramine has an elimination half-life of 20 hours in healthy subjects.
Protein Binding
Fenfluramine is 50% bound to plasma proteins independent of plasma drug concentration.
Elimination
Over 90% of fenfluramine is excreted in urine and less than 5% in feces; unchanged fenfluramine and the major active metabolite norfenfluramine account for less than 25% of the recovered amount.
Volume of Distribution
Fenfluramine has an apparent volume of distribution of 11.9 L/kg with a coefficient of variation of 16.5% following oral administration in healthy subjects.
Clearance
Fenfluramine has a mean clearance of 24.8 L/h with a coefficient of variation of 29% in healthy subjects.
Tolerance & Pharmacokinetics
drugs.wikiTolerance Decay
Robust human data describing pharmacodynamic tolerance to fenfluramine’s antiseizure effect are lacking; some tolerance to anorectic effects likely develops with repeated exposure, as seen historically with serotonergic anorectics, but magnitude and timeline are poorly characterized. Treat as unknown; avoid dose escalation outside medical guidance.
Cross-Tolerances
Harm Reduction
drugs.wikiRationale for updated harm reduction and medical-use guidance:
- Cardiac valvulopathy mechanism: Fenfluramine’s active metabolite norfenfluramine is a potent 5‑HT2B agonist on heart valves; activation drives fibroblast proliferation and valvular thickening. This mechanistic link is supported by receptor-binding and functional assays and is widely accepted as the likely cause of fenfluramine-associated valvular heart disease (VHD). Therefore, any non‑medical use is high risk, and medical use generally requires baseline and periodic echocardiography under restricted programs.
- Pulmonary arterial hypertension (PAH) has been associated historically with fenfluramine/dexfenfluramine exposure; although RCTs in Dravet syndrome did not detect PAH over short durations, the risk justifies ongoing cardiopulmonary monitoring and symptom education (dyspnea, syncope, edema).
- Dosing must follow mg/kg regimens used in epilepsy trials/labels: typical titration is from 0.1 mg/kg/day to 0.35 mg/kg/day in divided doses, with lower maxima when co‑administered with stiripentol + clobazam; exceeding these regimens increases cardiotoxic risk.
- Serotonergic risk: Fenfluramine increases extracellular serotonin and carries a stated risk of potentially fatal serotonin syndrome; combining with MAOIs, SSRIs/SNRIs, triptans, or serotonin releasers markedly elevates risk. Educate users to avoid such combinations and to recognize red‑flag symptoms (agitation, hyperthermia, clonus).
- Pharmacokinetics and interactions: Oral absorption is unaffected by food; elimination half‑life is ~20 h; it is metabolized by multiple CYPs (1A2, 2B6, 2D6, 2C9, 2C19, 3A4/5). This supports caution with strong inhibitors/inducers and justifies slow titration and tapering to avoid adverse effects or seizure destabilization.
- Sedation and anorexia are common adverse effects in RCTs; in pediatric patients, monitor weight, nutritional status, and fall risk; advise against driving/operating machinery during initiation/titration due to somnolence/ataxia.
- Restricted access programs (e.g., REMS) exist due to VHD/PAH risk; this underscores the need for supervised use and routine echocardiography.
- Discontinuation should be gradual to limit rebound issues (including seizure destabilization in treated populations).
Harm-reduction additions applied to the JSON above reflect these points: dosing corrected to mg/kg/day with stiripentol-specific maxima; interactions expanded with serotonergic, CYP, and CNS depressant cautions; subjective effects adjusted toward sedation/anorexia rather than stimulation; and notes emphasize cardiac monitoring and avoidance of non‑medical use.
References
Drugs.wiki References
- DrugBank: Fenfluramine DB00574
- PubMed 10617681: Possible role of 5‑HT2B receptors in fenfluramine cardiopathy (1999)
- PubMed 11104741: 5‑HT2B receptors implicated in drug‑induced VHD (2000)
- PMC2695569: Serotonergic drugs and valvular heart disease (2009 review)
- PubMed 31862249: Dravet RCT (0.2 and 0.7 mg/kg/day)
- PubMed 31790543: Dravet RCT with stiripentol-inclusive regimens (0.4 mg/kg/day; max 17 mg/day)
- PubMed 37543865: Third Dravet phase 3 trial (0.7 mg/kg/day)