Drug interactions
Phenylephrine + Timolol
Severity: Moderate
Phenylephrine and Timolol: 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
Nonselective beta-blockade leaves alpha-mediated vasoconstriction from phenylephrine unopposed, which can cause a marked rise in blood pressure with reflex bradycardia. This is mainly relevant with systemic phenylephrine or oral timolol, and is uncommon with eye drops.
What this interaction means in plain words
Phenylephrine and Timolol 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.
Phenylephrine belongs to Respiratory; Timolol belongs to Cardiovascular.
Why it happens
Blockade of beta-2 vasodilation leaves unopposed alpha-1 vasoconstriction, with reflex bradycardia.
What to do
Monitor blood pressure and heart rate when systemic phenylephrine is given to patients taking timolol. Use the lowest effective phenylephrine dose or choose a non-pressor alternative.
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 Timolol
- Acebutolol + Timolol Major
- Albuterol + Timolol Major
- Aldesleukin + Timolol Major
- Amifostine + Timolol Major
- Amiodarone + Timolol Major
- Arformoterol + Timolol Major
Frequently asked questions
Can I take Phenylephrine with Timolol?
MediHelp rates the interaction as moderate. Phenylephrine and Timolol 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. Nonselective beta-blockade leaves alpha-mediated vasoconstriction from phenylephrine unopposed, which can cause a marked rise in blood pressure with reflex bradycardia. This is mainly relevant with systemic phenylephrine or oral timolol, and is uncommon with eye drops.
How serious is the interaction between Phenylephrine and Timolol?
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 systemic phenylephrine is given to patients taking timolol. Use the lowest effective phenylephrine dose or choose a non-pressor alternative.
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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