Drug interactions
Fenfluramine + Promethazine
Severity: Moderate
Fenfluramine and Promethazine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Fenfluramine can cause somnolence and lowers seizure threshold in some settings, while promethazine is sedating and may also lower seizure threshold. Both CNS effects may be additive, and fenfluramine also carries serotonergic effects, though no specific significant interaction is firmly documented.
What this interaction means in plain words
Fenfluramine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Fenfluramine belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive CNS effects; no clearly established pharmacokinetic mechanism.
What to do
Monitor for excessive sedation and for changes in seizure frequency in patients with epilepsy.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Other interactions of Fenfluramine
- Fenfluramine + Isocarboxazid Contraindicated
- Fenfluramine + Linezolid Contraindicated
- Fenfluramine + Phenelzine Contraindicated
- Fenfluramine + Selegiline Contraindicated
- Fenfluramine + Tranylcypromine Contraindicated
- Almotriptan + Fenfluramine Major
Frequently asked questions
Can I take Fenfluramine with Promethazine?
MediHelp rates the interaction as moderate. Fenfluramine and Promethazine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Fenfluramine can cause somnolence and lowers seizure threshold in some settings, while promethazine is sedating and may also lower seizure threshold. Both CNS effects may be additive, and fenfluramine also carries serotonergic effects, though no specific significant interaction is firmly documented.
How serious is the interaction between Fenfluramine and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for excessive sedation and for changes in seizure frequency in patients with epilepsy.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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