Drug interactions
Fosphenytoin + Lorlatinib
Severity: Contraindicated
Fosphenytoin and Lorlatinib: contraindicated 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 strong CYP3A4 inducer. This lowers lorlatinib exposure substantially and risks loss of efficacy and hepatotoxicity.
What this interaction means in plain words
Fosphenytoin and Lorlatinib are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two.
Fosphenytoin belongs to Central Nervous System; Lorlatinib belongs to Oncology.
Why it happens
Phenytoin induces CYP3A4 and increases lorlatinib metabolism.
What to do
Avoid the combination and change to a non-inducing anticonvulsant such as levetiracetam. Allow a washout period before starting lorlatinib.
What to ask your pharmacist
- Is there an alternative to one of these two medicines for me?
- If both are essential, who is monitoring me and how often?
- Which symptoms mean I should stop and seek help straight away?
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Other interactions of Lorlatinib
- Amobarbital + Lorlatinib Contraindicated
- Apalutamide + Lorlatinib Contraindicated
- Butabarbital + Lorlatinib Contraindicated
- Carbamazepine + Lorlatinib Contraindicated
- Enzalutamide + Lorlatinib Contraindicated
- Lonafarnib + Lorlatinib Contraindicated
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
- Abiraterone + Fosphenytoin Major
Frequently asked questions
Can I take Fosphenytoin with Lorlatinib?
MediHelp rates the interaction as contraindicated. Fosphenytoin and Lorlatinib are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two. Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer. This lowers lorlatinib exposure substantially and risks loss of efficacy and hepatotoxicity.
How serious is the interaction between Fosphenytoin and Lorlatinib?
MediHelp rates it contraindicated, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination and change to a non-inducing anticonvulsant such as levetiracetam. Allow a washout period before starting lorlatinib.
What other medicines interact with Lorlatinib?
MediHelp also lists interactions of Lorlatinib with, for example, Amobarbital, Apalutamide, Butabarbital. The full list is on the Lorlatinib page.
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