Drug interactions
Fosphenytoin + Montelukast
Severity: Moderate
Fosphenytoin and Montelukast: 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 inducer of CYP3A4 and CYP2C enzymes, which may lower montelukast exposure. Loss of asthma control is possible with prolonged use.
What this interaction means in plain words
Fosphenytoin and Montelukast 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; Montelukast belongs to Respiratory.
Why it happens
Phenytoin induces CYP3A4 and CYP2C enzymes, increasing montelukast clearance.
What to do
Monitor asthma symptom control when fosphenytoin is started or stopped. Consider additional or alternative controller therapy if control is lost.
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 Montelukast
- Apalutamide + Montelukast Moderate
- Carbamazepine + Montelukast Moderate
- Deferasirox + Montelukast Moderate
- Enzalutamide + Montelukast Moderate
- Gemfibrozil + Montelukast Moderate
- Mitotane + Montelukast Moderate
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 Montelukast?
MediHelp rates the interaction as moderate. Fosphenytoin and Montelukast 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 inducer of CYP3A4 and CYP2C enzymes, which may lower montelukast exposure. Loss of asthma control is possible with prolonged use.
How serious is the interaction between Fosphenytoin and Montelukast?
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 asthma symptom control when fosphenytoin is started or stopped. Consider additional or alternative controller therapy if control is lost.
What other medicines interact with Montelukast?
MediHelp also lists interactions of Montelukast with, for example, Apalutamide, Carbamazepine, Deferasirox. The full list is on the Montelukast page.
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