Drug interactions
Fexofenadine + Phenytoin
Severity: Minor
Fexofenadine and Phenytoin: 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
Phenytoin is an inducer of drug transporters and enzymes and may increase P-glycoprotein expression, possibly lowering fexofenadine absorption. A reduced antihistamine effect is conceivable but poorly documented.
What this interaction means in plain words
Fexofenadine and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Fexofenadine belongs to Respiratory; Phenytoin belongs to Central Nervous System.
Why it happens
Possible induction of intestinal P-glycoprotein by phenytoin, reducing fexofenadine bioavailability.
What to do
No routine change is needed; if allergy symptom control worsens, consider increasing the dose within labeled limits or choosing another antihistamine.
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 Fexofenadine
- Danicopan + Fexofenadine Moderate
- Erdafitinib + Fexofenadine Moderate
- Fexofenadine + Glecaprevir / pibrentasvir Moderate
- Fexofenadine + Grapefruit Moderate
- Fexofenadine + Juice Moderate
- Acrivastine + Fexofenadine Minor
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
Frequently asked questions
Can I take Fexofenadine with Phenytoin?
MediHelp rates the interaction as minor. Fexofenadine and Phenytoin 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 is an inducer of drug transporters and enzymes and may increase P-glycoprotein expression, possibly lowering fexofenadine absorption. A reduced antihistamine effect is conceivable but poorly documented.
How serious is the interaction between Fexofenadine and Phenytoin?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No routine change is needed; if allergy symptom control worsens, consider increasing the dose within labeled limits or choosing another antihistamine.
What other medicines interact with Fexofenadine?
MediHelp also lists interactions of Fexofenadine with, for example, Danicopan, Erdafitinib, Glecaprevir / pibrentasvir. The full list is on the Fexofenadine page.
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