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. This can lead to loss of virologic response and possible resistance [see Contraindications (4)]. |
Neuromuscular blocking agents | Cisatracurium, pancuronium, rocuronium and vecuronium: resistance to the neuromuscular blocking action of the nondepolarizing neuromuscular blocking agents has occurred in patients chronically administered phenytoin. Whether or not phenytoin has the same effect on other non-depolarizing agents is unknown.-
- Prevention or Management: Patients should be monitored closely for more rapid recovery from neuromuscular blockade than expected, and infusion rate requirements may be higher.
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Warfarin | Increased and decreased PT/INR responses have been reported when phenytoin is coadministered with warfarin. |
Other | Corticosteroids, doxycycline, estrogens, furosemide, oral contraceptives, paroxetine, quinidine, rifampin, sertraline, theophylline, and vitamin D |
Drugs whose level is decreased by phenytoin |
Anticoagulants | Apixaban, dabigatran, edoxaban, rivaroxaban |
Antiepileptic drugs* | Carbamazepine, felbamate, lamotrigine, topiramate, oxcarbazepine, lacosamide |
Antiplatelets | Ticagrelor |
Antilipidemic agents | Atorvastatin, fluvastatin, simvastatin |
Antiviral agents | Efavirenz, lopinavir/ritonavir, indinavir, nelfinavir, ritonavir, saquinavir Fosamprenavir: phenytoin when given with fosamprenavir alone may decrease the concentration of amprenavir, the active metabolite. Phenytoin when given with the combination of fosamprenavir and ritonavir may increase the concentration of amprenavir |
Calcium channel blockers | Nifedipine, nimodipine, nisoldipine, verapamil |
Other | Albendazole (decreases active metabolite), chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine |