Phenytoin and Posaconazole interaction
Phenytoin and Posaconazole: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Posaconazole (NOXAFIL) label · effective 2026-02-13
Phenytoin Avoid concomitant use of posaconazole with phenytoin unless the benefit to the patient outweighs the risk.
Prevention or Management Avoid concomitant use of posaconazole with phenytoin unless the benefit outweighs the risk. frequently monitor phenytoin concentrations and consider a dosage reduction of phenytoin.
See Table 17 for phenytoin monitoring considerations when posaconazole affects phenytoin via CYP3A4 inhibition.
Concomitant use of posaconazole with phenytoin increased phenytoin plasma concentrations [see Clinical Pharmacology (12.3) ].
See Table 15 for additional monitoring considerations when phenytoin affects posaconazole via UDP-glucuronosyltransferase inhibition.
From the Phenytoin label · effective 2024-12-24
Table 3: Drugs Affected by Phenytoin Interacting Agent Examples Drugs whose efficacy is impaired by phenytoin Azoles Fluconazole, ketoconazole, itraconazole, posaconazole, voriconazole Antineoplastic agents Irinotecan, paclitaxel, teniposide Delavirdine Phenytoin can substantially reduce the concentrations of delavirdine.
…Phenytoin Concentrations Interacting Agent Examples Drugs that may increase phenytoin serum levels Antiepileptic drugs Ethosuximide, felbamate, oxcarbazepine, methsuximide, topiramate Azoles Fluconazole, ketoconazole, itraconazole, miconazole, voriconazole Antineoplastic agents Capecitabine, fluorouracil Antidepressants Fluoxetine, fluvoxamine, sertraline Gastric…
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.