Drug interactions
Fosphenytoin + Primaquine
Severity: Moderate
Fosphenytoin and Primaquine: 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
Fosphenytoin is converted to phenytoin, an enzyme inducer, which may lower primaquine concentrations and reduce its efficacy in radical cure. The clinical significance is predicted from the mechanism rather than well documented.
What this interaction means in plain words
Fosphenytoin and Primaquine 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.
Fosphenytoin belongs to Central Nervous System; Primaquine belongs to Anti Parasitic.
Why it happens
Phenytoin induces CYP enzymes including CYP3A4, increasing primaquine metabolism.
What to do
Monitor for treatment failure or relapse of malaria, or consider a non-inducing anticonvulsant if clinically feasible. Do not change antiepileptic therapy without neurology input.
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 Primaquine
- Pimozide + Primaquine Contraindicated
- Amiodarone + Primaquine Major
- Amisulpride + Primaquine Major
- Anagrelide + Primaquine Major
- Arsenic trioxide + Primaquine Major
- Asenapine + Primaquine 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 Fosphenytoin with Primaquine?
MediHelp rates the interaction as moderate. Fosphenytoin and Primaquine 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. Fosphenytoin is converted to phenytoin, an enzyme inducer, which may lower primaquine concentrations and reduce its efficacy in radical cure. The clinical significance is predicted from the mechanism rather than well documented.
How serious is the interaction between Fosphenytoin and Primaquine?
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 for treatment failure or relapse of malaria, or consider a non-inducing anticonvulsant if clinically feasible. Do not change antiepileptic therapy without neurology input.
What other medicines interact with Primaquine?
MediHelp also lists interactions of Primaquine with, for example, Pimozide, Amiodarone, Amisulpride. The full list is on the Primaquine page.
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