Drug interactions
Darunavir + Phenytoin
Severity: Major
Darunavir and Phenytoin: 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
Phenytoin can lower darunavir concentrations, risking virologic failure and resistance. Phenytoin levels may also fall when taken with ritonavir-boosted darunavir.
What this interaction means in plain words
Darunavir and Phenytoin 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.
Darunavir belongs to Anti Virals; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4 metabolism of darunavir and cobicistat or ritonavir boosters.
What to do
Avoid the combination and use a non-inducing anticonvulsant. If unavoidable, monitor HIV RNA and phenytoin concentrations.
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 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 Darunavir
- Alfuzosin + Darunavir Contraindicated
- Avanafil + Darunavir Contraindicated
- Darunavir + Dronedarone Contraindicated
- Darunavir + Eletriptan Contraindicated
- Darunavir + Ergotamine Contraindicated
- Darunavir + Flibanserin Contraindicated
Frequently asked questions
Can I take Darunavir with Phenytoin?
MediHelp rates the interaction as major. Darunavir and Phenytoin 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. Phenytoin can lower darunavir concentrations, risking virologic failure and resistance. Phenytoin levels may also fall when taken with ritonavir-boosted darunavir.
How serious is the interaction between Darunavir and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination and use a non-inducing anticonvulsant. If unavoidable, monitor HIV RNA and phenytoin concentrations.
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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