Drug interactions
Fosphenytoin + Metyrapone
Severity: Moderate
Fosphenytoin and Metyrapone: 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, a known enzyme inducer, and phenytoin is reported to reduce the response to metyrapone testing. Lower metyrapone exposure can cause loss of the expected cortisol suppression and can lead to misinterpretation of diagnostic testing or reduced treatment effect.
What this interaction means in plain words
Fosphenytoin and Metyrapone 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; Metyrapone belongs to Endocrine.
Why it happens
Phenytoin-mediated enzyme induction increases the metabolic clearance of metyrapone.
What to do
Monitor cortisol and precursor steroid levels and increase the metyrapone dose if needed. Take the anticonvulsant into account when interpreting metyrapone test results.
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 Metyrapone
- Metyrapone + Pacritinib Major
- Budesonide + Metyrapone Moderate
- Cortisone + Metyrapone Moderate
- Cyproheptadine + Metyrapone Moderate
- Deflazacort + Metyrapone Moderate
- Desogestrel-ethinyl estradiol + Metyrapone 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 Metyrapone?
MediHelp rates the interaction as moderate. Fosphenytoin and Metyrapone 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, a known enzyme inducer, and phenytoin is reported to reduce the response to metyrapone testing. Lower metyrapone exposure can cause loss of the expected cortisol suppression and can lead to misinterpretation of diagnostic testing or reduced treatment effect.
How serious is the interaction between Fosphenytoin and Metyrapone?
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 cortisol and precursor steroid levels and increase the metyrapone dose if needed. Take the anticonvulsant into account when interpreting metyrapone test results.
What other medicines interact with Metyrapone?
MediHelp also lists interactions of Metyrapone with, for example, Pacritinib, Budesonide, Cortisone. The full list is on the Metyrapone page.
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