Drug interactions
Fenfluramine + Phenylephrine
Severity: Moderate
Fenfluramine and Phenylephrine: 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 raises serotonergic and, to a lesser extent, noradrenergic tone, and phenylephrine is a direct vasoconstrictor. Used together they may increase blood pressure and heart rate beyond either drug alone. Fenfluramine also carries a risk of valvular disease and pulmonary hypertension, which makes pressor excess less desirable.
What this interaction means in plain words
Fenfluramine and Phenylephrine 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; Phenylephrine belongs to Respiratory.
Why it happens
Additive sympathomimetic pressor effects from direct alpha-1 agonism and fenfluramine-mediated monoamine release.
What to do
Monitor blood pressure and heart rate when starting or adjusting systemic phenylephrine in patients on fenfluramine. Avoid routine use of oral decongestants where possible.
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 Phenylephrine
- Isocarboxazid + Phenylephrine Contraindicated
- Phenelzine + Phenylephrine Contraindicated
- Phenylephrine + Tranylcypromine Contraindicated
- Bromocriptine + Phenylephrine Major
- Cocaine + Phenylephrine Major
- Dihydroergotamine intranasal + Phenylephrine 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 Phenylephrine?
MediHelp rates the interaction as moderate. Fenfluramine and Phenylephrine 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 raises serotonergic and, to a lesser extent, noradrenergic tone, and phenylephrine is a direct vasoconstrictor. Used together they may increase blood pressure and heart rate beyond either drug alone. Fenfluramine also carries a risk of valvular disease and pulmonary hypertension, which makes pressor excess less desirable.
How serious is the interaction between Fenfluramine and Phenylephrine?
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 blood pressure and heart rate when starting or adjusting systemic phenylephrine in patients on fenfluramine. Avoid routine use of oral decongestants where possible.
What other medicines interact with Phenylephrine?
MediHelp also lists interactions of Phenylephrine with, for example, Isocarboxazid, Phenelzine, Tranylcypromine. The full list is on the Phenylephrine page.
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