Increase phenytoin serum levels: Acute alcohol intake, dicoumarol, disulfiram, methylphenidate, omeprazole, ticlopidine, viloxazine, NSAID eg, salicylates, halothane, chloramphenicol, erythromycin, INH, sulfonamides, felbamate, succinimides, amphotericin B, fluconazole, ketoconazole, miconazole, itraconazole, benzodiazepines/psychotropic agents, amiodarone, diltiazem, nifedipine, estrogens, tolbutamide, fluoxetine. Decrease phenytoin serum levels: Fluoroquinolones, chronic alcohol abuse, diazoxide, reserpine, sucralfate, theophylline, vigabatrin, Ca-containing prep. Drugs which affect phenytoin: Anticonvulsants, chlordiazepoxide, diazepam. Drugs affected by phenytoin: Clozapine, corticosteroids, coumarin, anticoagulants, cyclosporine, diazoxide, furosemide, paroxetine, theophylline, vit D, doxycycline, rifampicin, praziquantel, tetracycline, OC, neuromuscular-blocking agents, methadone, sulfonylurea antidiabetic drugs.