May increase the unbound fraction w/ drugs highly bound to albumin. May increase phenytoin serum levels w/ acute alcohol intake, azapropazone, phenylbutazone, salicylates, halothane, chloramphenicol, erythromycin, INH, sulfadiazine, sulfamethizole, co-trimoxazole, sulfaphenazole, sulfisoxazole, sulfonamides, felbamate, oxcarbazepine, Na valproate, succinimides, topiramate, amphotericin B, fluconazole, itraconazole, ketoconazole, miconazole, voriconazole, fluorouracil, capecitabine, chlordiazepoxide, diazepam, disulfiram, methylphenidate, trazodone, viloxazine, amiodarone, dicumarol, diltiazem, nifedipine, ticlopidine, cimetidine, fluvastatin, estrogens, tacrolimus, tolbutamide, omeprazole, fluoxetine, fluvoxamine, sertraline. May decreased phenytoin serum levels w/ chronic alcohol intake, rifampin, ciprofloxacin, vigabatrin, bleomycin, carboplatin, cisplatin, doxorubicin, MTX, fosamprenavir, nelfinavir, ritonavir, theophylline, reserpine, folic acid, diazoxide, St. John's wort. May increase or decrease phenytoin serum levels w/ ciprofloxacin, carbamazepine, phenobarb, Na valproate, valproic acid, antineoplastic agents, chlordiazepoxide, diazepam, phenothiazines. Potential loss of virologic response & possible resistance to delavirdine. Increased risk of valproate-associated hyperammonemia in concomitant use of valproate. May cause decreased protein-bound iodine serum levels. May produce lower than normal values for dexamethasone or metyrapone test. May affect blood Ca & sugar metabolism tests.