Drug interactions
Doxycycline + Fosphenytoin
Severity: Moderate
Doxycycline and Fosphenytoin: 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, the active form of fosphenytoin, induces hepatic enzymes and shortens the half-life of doxycycline, potentially causing subtherapeutic antibiotic levels. This can lead to treatment failure, especially with prolonged phenytoin use.
What this interaction means in plain words
Doxycycline and Fosphenytoin 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; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin-mediated hepatic enzyme induction increases doxycycline clearance.
What to do
Consider increasing doxycycline dose frequency (for example twice daily) or choosing an alternative antibiotic, and 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 Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Doxycycline with Fosphenytoin?
MediHelp rates the interaction as moderate. Doxycycline and Fosphenytoin 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, the active form of fosphenytoin, induces hepatic enzymes and shortens the half-life of doxycycline, potentially causing subtherapeutic antibiotic levels. This can lead to treatment failure, especially with prolonged phenytoin use.
How serious is the interaction between Doxycycline and Fosphenytoin?
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 doxycycline dose frequency (for example twice daily) or choosing an alternative antibiotic, and 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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