Drug interactions
Lorlatinib + Phenytoin
Severity: Contraindicated
Lorlatinib and Phenytoin: contraindicated interaction.
Last updated Sources: UK SmPC
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
Phenytoin strongly induces CYP3A4 and markedly reduces lorlatinib exposure, risking loss of anticancer efficacy. Strong CYP3A inducers are contraindicated with lorlatinib, and hepatotoxicity has also been seen.
What this interaction means in plain words
Lorlatinib and Phenytoin 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.
Lorlatinib belongs to Oncology; Phenytoin belongs to Central Nervous System.
Why it happens
CYP3A4 induction increasing lorlatinib metabolism.
What to do
Do not combine; switch to a non-inducing anticonvulsant such as levetiracetam.
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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References
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Other interactions of Lorlatinib
- Amobarbital + Lorlatinib Contraindicated
- Apalutamide + Lorlatinib Contraindicated
- Butabarbital + Lorlatinib Contraindicated
- Carbamazepine + Lorlatinib Contraindicated
- Enzalutamide + Lorlatinib Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
Frequently asked questions
Can I take Lorlatinib with Phenytoin?
MediHelp rates the interaction as contraindicated. Lorlatinib and Phenytoin 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. Phenytoin strongly induces CYP3A4 and markedly reduces lorlatinib exposure, risking loss of anticancer efficacy. Strong CYP3A inducers are contraindicated with lorlatinib, and hepatotoxicity has also been seen.
How serious is the interaction between Lorlatinib and Phenytoin?
MediHelp rates it contraindicated, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Do not combine; switch to a non-inducing anticonvulsant such as levetiracetam.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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