Drug interactions
Fosphenytoin + Ifosfamide
Severity: Major
Fosphenytoin and Ifosfamide: major interaction.
Last updated Sources: US FDA label
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, which induces CYP3A4 and CYP2B6 and can increase ifosfamide conversion to toxic metabolites such as chloroacetaldehyde. This may increase encephalopathy and nephrotoxicity risk, and ifosfamide neurotoxicity may itself provoke seizures.
What this interaction means in plain words
Fosphenytoin and Ifosfamide can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Fosphenytoin belongs to Central Nervous System; Ifosfamide belongs to Oncology.
Why it happens
Induction of CYP3A4 and CYP2B6 by phenytoin increases ifosfamide metabolism and toxic metabolite formation.
What to do
Monitor for neurotoxicity, renal function and marrow suppression, and consider a non-inducing anticonvulsant such as levetiracetam. Adjust the ifosfamide dose if toxicity occurs.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Ifosfamide
- Adenovirus types 4 and 7 live + Ifosfamide Contraindicated
- Ifosfamide + Measles mumps and rubella vaccine Contraindicated
- Ifosfamide + Measles mumps and rubella vaccine live Contraindicated
- Ifosfamide + Measles mumps rubella and varicella vaccine live Contraindicated
- Ifosfamide + Measles vaccine Contraindicated
- Ifosfamide + Rotavirus oral 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 Ifosfamide?
MediHelp rates the interaction as major. Fosphenytoin and Ifosfamide can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Fosphenytoin is converted to phenytoin, which induces CYP3A4 and CYP2B6 and can increase ifosfamide conversion to toxic metabolites such as chloroacetaldehyde. This may increase encephalopathy and nephrotoxicity risk, and ifosfamide neurotoxicity may itself provoke seizures.
How serious is the interaction between Fosphenytoin and Ifosfamide?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for neurotoxicity, renal function and marrow suppression, and consider a non-inducing anticonvulsant such as levetiracetam. Adjust the ifosfamide dose if toxicity occurs.
What other medicines interact with Ifosfamide?
MediHelp also lists interactions of Ifosfamide with, for example, Adenovirus types 4 and 7 live, Measles mumps and rubella vaccine, Measles mumps and rubella vaccine live. The full list is on the Ifosfamide page.
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