Drug interactions
Doxycycline + Phenytoin
Severity: Moderate
Doxycycline and Phenytoin: 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
Phenytoin induces hepatic enzymes and shortens the half-life of doxycycline, which can lower its concentrations. This may lead to subtherapeutic antibiotic exposure and treatment failure.
What this interaction means in plain words
Doxycycline and Phenytoin 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.
Doxycycline belongs to Anti Bacterial; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces hepatic microsomal enzymes, increasing doxycycline clearance.
What to do
Consider increasing the doxycycline dose (for example twice-daily dosing) or choosing an alternative antibiotic. Monitor clinical response.
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 Doxycycline
- Acitretin + Doxycycline Contraindicated
- Aminolevulinic acid + Doxycycline Major
- Cholera vaccine + Doxycycline Major
- Doxycycline + Isotretinoin Major
- Doxycycline + Methoxyflurane Major
- Doxycycline + Microbiota Major
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 Doxycycline with Phenytoin?
MediHelp rates the interaction as moderate. Doxycycline and Phenytoin 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. Phenytoin induces hepatic enzymes and shortens the half-life of doxycycline, which can lower its concentrations. This may lead to subtherapeutic antibiotic exposure and treatment failure.
How serious is the interaction between Doxycycline and Phenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Consider increasing the doxycycline dose (for example twice-daily dosing) or choosing an alternative antibiotic. Monitor clinical response.
What other medicines interact with Doxycycline?
MediHelp also lists interactions of Doxycycline with, for example, Acitretin, Aminolevulinic acid, Cholera vaccine. The full list is on the Doxycycline page.
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