Drug interactions
Diphenhydramine + Timolol
Severity: Moderate
Diphenhydramine 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
Diphenhydramine inhibits CYP2D6 and may reduce timolol clearance, increasing beta-blocker effects. This could cause more bradycardia or hypotension, particularly with oral timolol or in patients who are poor CYP2D6 metabolizers. Occasional antihistamine use is unlikely to matter much.
What this interaction means in plain words
Diphenhydramine 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.
Diphenhydramine belongs to Respiratory; Timolol belongs to Cardiovascular.
Why it happens
Inhibition of CYP2D6-mediated timolol metabolism by diphenhydramine.
What to do
Monitor heart rate and blood pressure when diphenhydramine is used regularly with timolol. Reduce the timolol dose if symptomatic bradycardia or hypotension develops.
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 Timolol
- Acebutolol + Timolol Major
- Aldesleukin + Timolol Major
- Amifostine + Timolol Major
- Amiodarone + Timolol Major
- Arformoterol + Timolol Major
- Atenolol-chlorthalidone + Timolol Major
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Timolol?
MediHelp rates the interaction as moderate. Diphenhydramine 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. Diphenhydramine inhibits CYP2D6 and may reduce timolol clearance, increasing beta-blocker effects. This could cause more bradycardia or hypotension, particularly with oral timolol or in patients who are poor CYP2D6 metabolizers. Occasional antihistamine use is unlikely to matter much.
How serious is the interaction between Diphenhydramine 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 heart rate and blood pressure when diphenhydramine is used regularly with timolol. Reduce the timolol dose if symptomatic bradycardia or hypotension develops.
What other medicines interact with Timolol?
MediHelp also lists interactions of Timolol with, for example, Acebutolol, Aldesleukin, Amifostine. The full list is on the Timolol page.
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