Drug interactions
Phenoxybenzamine + Phenylephrine
Severity: Moderate
Phenoxybenzamine 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
Phenoxybenzamine causes irreversible alpha-adrenergic blockade, which counteracts the vasoconstriction and pressor effect of phenylephrine. Higher phenylephrine doses may be needed to raise blood pressure, and the response can be unpredictable.
What this interaction means in plain words
Phenoxybenzamine 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.
Why it happens
Pharmacodynamic antagonism through irreversible blockade of alpha-adrenergic receptors.
What to do
Monitor blood pressure closely when phenylephrine is given to a patient on phenoxybenzamine, and titrate the vasopressor to effect. Avoid phenylephrine as a decongestant in these patients.
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
Frequently asked questions
Can I take Phenoxybenzamine with Phenylephrine?
MediHelp rates the interaction as moderate. Phenoxybenzamine 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. Phenoxybenzamine causes irreversible alpha-adrenergic blockade, which counteracts the vasoconstriction and pressor effect of phenylephrine. Higher phenylephrine doses may be needed to raise blood pressure, and the response can be unpredictable.
How serious is the interaction between Phenoxybenzamine 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 closely when phenylephrine is given to a patient on phenoxybenzamine, and titrate the vasopressor to effect. Avoid phenylephrine as a decongestant in these patients.
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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