Drug interactions
Epinephrine + Phenoxybenzamine
Severity: Major
Epinephrine and Phenoxybenzamine: major interaction.
Last updated Sources: US FDA label
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 irreversibly blocks alpha-adrenergic receptors, so epinephrine's vasoconstrictor effect is lost while its beta-2 vasodilating and cardiac effects persist. This can cause pronounced hypotension and reflex tachycardia, which may be hard to correct.
What this interaction means in plain words
Epinephrine and Phenoxybenzamine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Alpha-adrenergic blockade leaves epinephrine's beta-mediated vasodilation and cardiac stimulation unopposed (epinephrine reversal).
What to do
Avoid epinephrine for hypotension in patients on phenoxybenzamine and use a pure alpha agonist such as phenylephrine or norepinephrine if a vasopressor is needed. If epinephrine is unavoidable, as in anaphylaxis, monitor blood pressure continuously and give fluids.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Epinephrine
- Epinephrine + Isocarboxazid Contraindicated
- Epinephrine + Phenelzine Contraindicated
- Epinephrine + Tranylcypromine Contraindicated
- Acebutolol + Epinephrine Major
- Amitriptyline + Epinephrine Major
- Amoxapine + Epinephrine Major
Frequently asked questions
Can I take Epinephrine with Phenoxybenzamine?
MediHelp rates the interaction as major. Epinephrine and Phenoxybenzamine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Phenoxybenzamine irreversibly blocks alpha-adrenergic receptors, so epinephrine's vasoconstrictor effect is lost while its beta-2 vasodilating and cardiac effects persist. This can cause pronounced hypotension and reflex tachycardia, which may be hard to correct.
How serious is the interaction between Epinephrine and Phenoxybenzamine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid epinephrine for hypotension in patients on phenoxybenzamine and use a pure alpha agonist such as phenylephrine or norepinephrine if a vasopressor is needed. If epinephrine is unavoidable, as in anaphylaxis, monitor blood pressure continuously and give fluids.
What other medicines interact with Epinephrine?
MediHelp also lists interactions of Epinephrine with, for example, Isocarboxazid, Phenelzine, Tranylcypromine. The full list is on the Epinephrine page.
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