Stiripentol vs. Fenfluramine: How Their Mechanisms Differ
Stiripentol and fenfluramine, both used in epilepsy treatment, operate through distinct primary mechanisms of action. Stiripentol primarily enhances the activity of gamma-aminobutyric acid (GABA), the brain's main inhibitory neurotransmitter, by interacting with GABA-A receptors [1]. It also inhibits some cytochrome P450 enzymes, which can affect the metabolism of other anti-epileptic drugs [1]. Fenfluramine, on the other hand, works by increasing serotonin release and activity in the brain [2]. This serotonergic action is thought to be its main anti-seizure effect, particularly in certain genetic epilepsies [2].
What is Stiripentol's Primary Action?
Stiripentol's core function in treating epilepsy is its positive allosteric modulation of GABA-A receptors [1]. This means it binds to a site on the receptor different from GABA itself, making the receptor more responsive to GABA and increasing inhibitory neurotransmission [1]. This dampens neuronal excitability, which is a hallmark of seizure activity.
How Does Fenfluramine Affect Seizures?
Fenfluramine's anti-seizure effects are largely attributed to its impact on the serotonergic system [2]. It promotes the release of serotonin from presynaptic neurons and may also inhibit its reuptake, leading to higher levels of serotonin in the synaptic cleft [2]. This increased serotonergic activity is believed to have a stabilizing effect on neuronal networks, reducing the likelihood of seizures.
Are There Other Ways These Drugs Work?
Beyond their primary mechanisms, stiripentol has been noted to inhibit certain cytochrome P450 enzymes, specifically CYP1A2, CYP2C19, and CYP3A4 [1]. This can lead to increased levels of other anti-epileptic drugs that are metabolized by these enzymes, potentially enhancing their efficacy but also their side effects [1]. Fenfluramine's direct impact on other neurotransmitter systems is less characterized as a primary mechanism for its anti-epileptic effects, though its serotonergic action is complex and may involve multiple receptor subtypes [2].
What Side Effects Are Associated with Each?
Stiripentol is associated with side effects such as somnolence, anorexia, weight decrease, and sometimes agitation or ataxia [1]. Fenfluramine's side effects are a significant area of concern, particularly its potential for cardiac valvulopathy and pulmonary arterial hypertension when used long-term or at higher doses, which led to its withdrawal from the market for weight loss in the past [2, 3]. However, in the context of epilepsy treatment, these risks are carefully managed [2, 3]. Other reported side effects can include fatigue, diarrhea, and decreased appetite [2].
Sources
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6809521/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7925170/
3. https://www.ema.europa.eu/en/documents/overview/fintepla-epar-public-assessment-report_en.pdf