Drug interactions
Phentolamine + Timolol
Severity: Moderate
Phentolamine 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
Phentolamine is an alpha-blocker vasodilator that can cause marked hypotension and reflex tachycardia. Timolol adds to the blood pressure lowering and blunts the compensatory tachycardia. Excessive hypotension is possible, especially with injected phentolamine.
What this interaction means in plain words
Phentolamine 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.
Phentolamine belongs to Cardiovascular; Timolol belongs to Cardiovascular.
Why it happens
Additive hypotensive effects from alpha-adrenergic blockade and beta-adrenergic blockade.
What to do
Monitor blood pressure and heart rate closely when phentolamine is given to patients taking timolol. Use the lowest effective phentolamine dose.
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
- Albuterol + Timolol Major
- Aldesleukin + Timolol Major
- Amifostine + Timolol Major
- Amiodarone + Timolol Major
- Arformoterol + Timolol Major
Other interactions of Phentolamine
Frequently asked questions
Can I take Phentolamine with Timolol?
MediHelp rates the interaction as moderate. Phentolamine 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. Phentolamine is an alpha-blocker vasodilator that can cause marked hypotension and reflex tachycardia. Timolol adds to the blood pressure lowering and blunts the compensatory tachycardia. Excessive hypotension is possible, especially with injected phentolamine.
How serious is the interaction between Phentolamine 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 closely when phentolamine is given to patients taking timolol. Use the lowest effective phentolamine dose.
What other medicines interact with Timolol?
MediHelp also lists interactions of Timolol with, for example, Acebutolol, Albuterol, Aldesleukin. The full list is on the Timolol page.
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