Drug interactions
Fosphenytoin + Leflunomide
Severity: Moderate
Fosphenytoin and Leflunomide: 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
Teriflunomide, the active metabolite of leflunomide, weakly inhibits CYP2C9, which is a main route of phenytoin clearance. Phenytoin levels may rise modestly, and because phenytoin has a narrow therapeutic index this could cause nystagmus, ataxia or sedation.
What this interaction means in plain words
Fosphenytoin and Leflunomide 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; Leflunomide belongs to Musculoskeletal.
Why it happens
Teriflunomide inhibits CYP2C9, reducing phenytoin metabolism.
What to do
Monitor phenytoin concentrations and for signs of toxicity after starting leflunomide. Adjust the fosphenytoin dose according to levels and 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 Leflunomide
- Bcg vaccine live + Leflunomide Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Leflunomide Contraindicated
- Leflunomide + Measles mumps and rubella vaccine live Contraindicated
- Leflunomide + Measles mumps rubella and varicella vaccine live Contraindicated
- Leflunomide + Measles vaccine Contraindicated
- Leflunomide + Smallpox vaccine live Contraindicated
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 Leflunomide?
MediHelp rates the interaction as moderate. Fosphenytoin and Leflunomide 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. Teriflunomide, the active metabolite of leflunomide, weakly inhibits CYP2C9, which is a main route of phenytoin clearance. Phenytoin levels may rise modestly, and because phenytoin has a narrow therapeutic index this could cause nystagmus, ataxia or sedation.
How serious is the interaction between Fosphenytoin and Leflunomide?
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 phenytoin concentrations and for signs of toxicity after starting leflunomide. Adjust the fosphenytoin dose according to levels and clinical response.
What other medicines interact with Leflunomide?
MediHelp also lists interactions of Leflunomide with, for example, Bcg vaccine live, Influenza virus vaccine quadrivalent intranasal, Measles mumps and rubella vaccine live. The full list is on the Leflunomide page.
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