Fenfluramine was developed in the early 1960s and was first introduced for medical use as an appetite suppressant in France in 1963 followed by approval in the United States in 1973.[8] In the 1990s, fenfluramine came to be associated with cardiovascular toxicity, and because of this, was withdrawn from the United States market in 1997.[8][16] Subsequently, it was repurposed for the treatment of seizures and was reintroduced in the United States and the European Union in 2020.[7][4][9] Fenfluramine was previously a schedule IVcontrolled substance in the United States.[7] However, the substance has since no-longer been subject to control pursuant to rule-making issued on 23 December 2022.[17]
Dravet syndrome is a life-threatening, rare and chronic form of epilepsy.[7] It is often characterized by severe and unrelenting seizures despite medical treatment.[7]
The most common adverse reactions in people with seizures include decreased appetite; drowsiness, sedation and lethargy; diarrhea; constipation; abnormal echocardiogram; fatigue or lack of energy; ataxia (lack of coordination), balance disorder, gait disturbance (trouble with walking); increased blood pressure; drooling, salivary hypersecretion (saliva overproduction); pyrexia (fever); upper respiratory tract infection; vomiting; decreased weight; risk of falls; and status epilepticus.[7]
The U.S. Food and Drug Administration (FDA) fenfluramine labeling includes a boxed warning stating the drug is associated with valvular heart disease (VHD) and pulmonary arterial hypertension (PAH).[7] Because of the risks of VHD and PAH, fenfluramine is available only through a restricted drug distribution program, under a risk evaluation and mitigation strategy (REMS).[7] The fenfluramine REMS requires health care professionals who prescribe fenfluramine and pharmacies that dispense fenfluramine to be specially certified in the fenfluramine REMS and that patients be enrolled in the REMS.[7] As part of the REMS requirements, prescribers and patients must adhere to the required cardiac monitoring with echocardiograms to receive fenfluramine.[7]
The distinctive valvular abnormality seen with fenfluramine is a thickening of the leaflet and chordae tendineae. One mechanism used to explain this phenomenon involves heart valve serotonin receptors, which are thought to help regulate growth. Since fenfluramine and its active metabolite norfenfluramine stimulate serotonin receptors, this may have led to the valvular abnormalities found in patients using fenfluramine. In particular norfenfluramine is a potent inhibitor of the re-uptake of 5-HT into nerve terminals.[22] Fenfluramine and its active metabolite norfenfluramine affect the 5-HT2B receptors, which are plentiful in human cardiac valves. The suggested mechanism by which fenfluramine causes damage is through over or inappropriate stimulation of these receptors leading to inappropriate valve cell division. Supporting this idea is the fact that this valve abnormality has also occurred in patients using other drugs that act on 5-HT2B receptors.[23][24]
According to a study of 5,743 former users conducted by a plaintiff's expert cardiologist, damage to the heart valve continued long after stopping the medication.[25] Of the users tested, 20% of women, and 12% of men were affected. For all ex-users, there was a 7-fold increase of chances of needing surgery for faulty heart valves caused by the drug.[25]
Fenfluramine was identified as a potentpositive modulator of the σ1 receptor in 2020 and this action may be involved in its therapeutic benefits in the treatment of seizures.[13][14]
In spite of acting as a serotonin 5-HT2A receptor agonist, fenfluramine has been described as non-hallucinogenic.[34] However, hallucinations have occasionally been reported when large doses of fenfluramine are taken.[34]
Pharmacokinetics
The elimination half-life of fenfluramine has been reported as ranging from 13 to 30 hours.[6] The mean elimination half-lives of its enantiomers have been found to be 19 hours for dexfenfluramine and 25 hours for levfenfluramine.[8] Norfenfluramine, the major active metabolite of fenfluramine, has an elimination half-life that is about 1.5 to 2 times as long as that of fenfluramine, with mean values of 34 hours for dexnorfenfluramine and 50 hours for levnorfenfluramine.[8]
Fenfluramine was developed in the early 1960s and was introduced in France in 1963.[8] Approximately 50 million Europeans were treated with fenfluramine for appetite suppression between 1963 and 1996.[8] Fenfluramine was approved in the United States in 1973.[8] The combination of fenfluramine and phentermine was proposed in 1984.[8] Approximately 5 million people in the United States were given fenfluramine or dexfenfluramine with or without phentermine between 1996 and 1998.[8]
In the early 1990s, French researchers reported an association of fenfluramine with primary pulmonary hypertension and dyspnea in a small sample of patients.[8] Fenfluramine was withdrawn from the U.S. market in 1997 after reports of heart valve disease[35][16] and continued findings of pulmonary hypertension, including a condition known as cardiac fibrosis.[36] It was subsequently withdrawn from other markets around the world. It was banned in India in 1998.[37]
In June 2020, fenfluramine was approved for medical use in the United States with an indication to treat Dravet syndrome.[7][38]
The effectiveness of fenfluramine for the treatment of seizures associated with Dravet syndrome was demonstrated in two clinical studies in 202 subjects between ages two and eighteen.[7] The studies measured the change from baseline in the frequency of convulsive seizures.[7] In both studies, subjects treated with fenfluramine had significantly greater reductions in the frequency of convulsive seizures during the trials than subjects who received placebo (inactive treatment).[7] These reductions were seen within 3–4 weeks, and remained generally consistent over the 14- to 15-week treatment periods.[7]
On 15 October 2020, the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion, recommending the granting of a marketing authorization for the medicinal product Fintepla, intended for the treatment of seizures associated with Dravet syndrome.[41] Fenfluramine was approved for medical use in the European Union in December 2020.[4]
Society and culture
Legal status
Fenfluramine is a prescription medication in the US. Fenfluramine was removed from Schedule IV of the Controlled Substances Act in December 2022.[42]
^ abcOdi R, Invernizzi RW, Gallily T, Bialer M, Perucca E (October 2021). "Fenfluramine repurposing from weight loss to epilepsy: What we do and do not know". Pharmacol Ther. 226: 107866. doi:10.1016/j.pharmthera.2021.107866. PMID33895186.
^Vickers SP, Dourish CT, Kennett GA (2001). "Evidence that hypophagia induced by d-fenfluramine and d-norfenfluramine in the rat is mediated by 5-HT2C receptors". Neuropharmacology. 41 (2): 200–9. doi:10.1016/s0028-3908(01)00063-6. PMID11489456. S2CID23374227.
^ abcdefghiRothman RB, Clark RD, Partilla JS, Baumann MH (2003). "(+)-Fenfluramine and its major metabolite, (+)-norfenfluramine, are potent substrates for norepinephrine transporters". J. Pharmacol. Exp. Ther. 305 (3): 1191–9. doi:10.1124/jpet.103.049684. PMID12649307. S2CID21164342.
^ abcdefgSetola V, Hufeisen SJ, Grande-Allen KJ, Vesely I, Glennon RA, Blough B, et al. (2003). "3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") induces fenfluramine-like proliferative actions on human cardiac valvular interstitial cells in vitro". Mol. Pharmacol. 63 (6): 1223–9. doi:10.1124/mol.63.6.1223. PMID12761331. S2CID839426.
^Nestler EJ (2001). Molecular Neuropharmacology: A Foundation for Clinical Neuroscience. McGraw-Hill.
^Fitzgerald LW, Burn TC, Brown BS, Patterson JP, Corjay MH, Valentine PA, et al. (2000). "Possible role of valvular serotonin 5-HT(2B) receptors in the cardiopathy associated with fenfluramine". Mol. Pharmacol. 57 (1): 75–81. PMID10617681.
^"Drugs banned in India". Central Drugs Standard Control Organization, Dte.GHS, Ministry of Health and Family Welfare, Government of India. Archived from the original on 21 February 2015. Retrieved 17 September 2013.
^"Fintepla: Pending EC decision". European Medicines Agency (EMA). 16 October 2020. Archived from the original on 21 October 2020. Retrieved 16 October 2020. Text was copied from this source which is copyright European Medicines Agency. Reproduction is authorized provided the source is acknowledged.
^ abGunne LM (1977). "Effects of Amphetamines in Humans". Drug Addiction II: Amphetamine, Psychotogen, and Marihuana Dependence. Berlin, Germany; Heidelberg, Germany: Springer. pp. 247–260. ISBN9783642667091. However, LEVIN recently (1972, 1974) reported on abuse of fenfluramine among LSD and cannabis abusers in South Africa. This group of abusers seems to have appreciated the hallucinogenic LSD-Iike effects, which fenfluramine exerts when applied in high doses (200—600 mg). At this dose level, the fenfluramine abusers (a total of 115) experienced euphoria with laughing attacks, followed some hours later by depressive symptoms. They reported visual and olfactory hallucinations, anxiety, sometimes with attacks of panic, nausea, and diarrhea.
^Connell PH (1979). "Drug dependence liability of anorectic drugs: a clinical viewpoint, with particular reference to fenfluramine". Current Medical Research and Opinion. 6 (sup1): 153–159. doi:10.1185/03007997909117502. ISSN0300-7995. Griffith et a1.6 compared fenfluramine with d-amphetamine and noted that fenfluramine was usually identified as LSD by subjects, and LSD scale scores after fenfluramine were significantly elevated. Three subjects receiving 240 mg fenfluramine experienced a psychedelic state characterized by visual and olfactory hallucination, cyclic alterations of mood, distorted time sense, fleeting paranoia, and sexual ideation. They noted that fenfluramine was a weak hallucinogen and, although sharing some features in common with amphetamine, "its overall profile of effects is quite different".
^Griffith JD (1977). "Structure-Activity Relationships of Several Amphetamine Drugs in Man". Cocaine and Other Stimulants. Vol. 21. Boston, MA: Springer US. p. 705–715. doi:10.1007/978-1-4684-3087-5_36. ISBN978-1-4684-3089-9. Fenfluramine (60, 120, 240 mg orally) [...] caused a marked dilation of pupils and elevation of the LSD Scale. [...] Fenfluramine was more often identified as an "LSD" or "barbiturate-like" substance. An unexpected response [...] was observed among 3 subjects who manifested hallucinatory states characterized by visual and olfactory hallucinations, rapid and polar changes of mood, distorted time sense, fleeting paranoia, and sexual hallucinations. [...] The remaining five subjects receiving the largest dose of fenfluramine experienced a chlorpromazine-like sedation without hallucinations or other psychedelic effects (Griffith, Nutt, and Jasinski, 1975). Chlorphentermine (50, 100, 200 mg) was similarly assessed. In certain respects, chlorphentermine resembles fenfluramine (Fig. 4), especially in terms of its mydriatic and sedative effects [...] On the other hand, chlorphentermine [...] is not hallucinogenic. [...] the utility of [amphetamine aromatic ring substitution] may be limited by the emergence of certain side-effects [...] e.g., dysphoria, sedation, and/or psychedelic properties.
^Griffith JD, Nutt JG, Jasinski DR (November 1975). "A comparison of fenfluramine and amphetamine in man". Clin Pharmacol Ther. 18 (5 Pt 1): 563–570. doi:10.1002/cpt1975185part1563. PMID1102234. dl-Fenfluramine hydrochloride (60, 120, 240 mg), d-amphetamine sulfate (20, 40 mg), and placebo were compared in 8 postaddict volunteers, each dose given orally [...] Fenfluramine [...] caused a marked dilation of pupils [...] While fenfluramine produced euphoria in some subjects, its overall effects were unpleasant, sedative, and qualitatively different from amphetamine. Three subjects given 240 mg of fenfluramine experienced brief but vivid hallucinogenic episodes characterized by olfactory, visual, and somatic hallucinations, abrupt polar changes in mood, time distortion, fleeting paranoia, and sexual ideation. These observations indicate that fenfluramine is a hallucinogenic agent with a pharmacologic profile in man that is not amphetamine-like.
^ abBrauer LH, Johanson CE, Schuster CR, Rothman RB, de Wit H (April 1996). "Evaluation of phentermine and fenfluramine, alone and in combination, in normal, healthy volunteers". Neuropsychopharmacology. 14 (4): 233–241. doi:10.1016/0893-133X(95)00113-R. PMID8924191.
^Cherek DR, Lane SD (September 2001). "Acute effects of D-fenfluramine on simultaneous measures of aggressive escape and impulsive responses of adult males with and without a history of conduct disorder". Psychopharmacology (Berl). 157 (3): 221–227. doi:10.1007/s002130100812. PMID11605076.
^Hetem LA, de Souza CJ, Guimarães ES, Zuardi AW, Graeff FG (October 1996). "Effect of d-fenfluramine on human experimental anxiety". Psychopharmacology (Berl). 127 (3): 276–282. PMID8912406.
^Aman MG, Kern RA (July 1989). "Review of fenfluramine in the treatment of the developmental disabilities". J Am Acad Child Adolesc Psychiatry. 28 (4): 549–565. doi:10.1097/00004583-198907000-00014. PMID2670881.
^Behera HK, Joga R, Yerram S, Karnati P, Mergu T, Gandhi K, et al. (September 2024). "Exploring the regulatory framework of psychedelics in the US & Europe". Asian J Psychiatr. 102: 104242. doi:10.1016/j.ajp.2024.104242. PMID39305768.
^Markopoulos A, Inserra A, De Gregorio D, Gobbi G (2021). "Evaluating the Potential Use of Serotonergic Psychedelics in Autism Spectrum Disorder". Front Pharmacol. 12: 749068. doi:10.3389/fphar.2021.749068. PMC8846292. PMID35177979. Fenfluramine, a serotonin-releasing agent, enhances serotonin signaling in the brain. While few small-sample, placebo-controlled studies found moderate efficacy in fenfluramine's ability to increase IQ in individuals with ASD (Geller et al., 1982; Ritvo et al., 1984), far more have found that this treatment is only effective in mildy reducing some of the motor and attentional atypicalities in people with ASD. This data suggests that increasing brain serotonin levels (and consequently serotonin signaling) is generally ineffective in improving the behavioural condition of individuals with ASD.
^Kostrzewa RM (2022). "Survey of Selective Monoaminergic Neurotoxins Targeting Dopaminergic, Noradrenergic, and Serotoninergic Neurons". Handbook of Neurotoxicity. Cham: Springer International Publishing. pp. 159–198. doi:10.1007/978-3-031-15080-7_53. ISBN978-3-031-15079-1.
^McCann UD, Seiden LS, Rubin LJ, Ricaurte GA (August 1997). "Brain serotonin neurotoxicity and primary pulmonary hypertension from fenfluramine and dexfenfluramine. A systematic review of the evidence". JAMA. 278 (8): 666–672. doi:10.1001/jama.1997.03550080076043. PMID9272900.
^Johnson MP, Nichols DE (May 1990). "Comparative serotonin neurotoxicity of the stereoisomers of fenfluramine and norfenfluramine". Pharmacol Biochem Behav. 36 (1): 105–109. doi:10.1016/0091-3057(90)90133-3. PMID2140899.