Drug interactions
Phenytoin + Tetracaine
Severity: Minor
Phenytoin and Tetracaine: minor 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
Both drugs have been associated with methemoglobinemia, so combined use could add to the risk. With topical tetracaine and limited systemic absorption, the risk is low in most patients.
What this interaction means in plain words
Phenytoin and Tetracaine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Phenytoin belongs to Central Nervous System; Tetracaine belongs to Central Nervous System.
Why it happens
Additive potential to oxidize hemoglobin to methemoglobin.
What to do
Avoid excessive tetracaine dosing on large or broken skin areas or mucosa, and monitor for cyanosis or low pulse oximetry.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Other interactions of Tetracaine
- Chloroquine + Tetracaine Moderate
- Dapsone + Tetracaine Moderate
- Isosorbide dinitrate + Tetracaine Moderate
- Isosorbide mononitrate + Tetracaine Moderate
- Nitrofurantoin + Tetracaine Moderate
- Nitroglycerin + Tetracaine Moderate
Frequently asked questions
Can I take Phenytoin with Tetracaine?
MediHelp rates the interaction as minor. Phenytoin and Tetracaine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Both drugs have been associated with methemoglobinemia, so combined use could add to the risk. With topical tetracaine and limited systemic absorption, the risk is low in most patients.
How serious is the interaction between Phenytoin and Tetracaine?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid excessive tetracaine dosing on large or broken skin areas or mucosa, and monitor for cyanosis or low pulse oximetry.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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