Increased risk for pseudotumor cerebri (benign/idiopathic intracranial HTN) w/ agents causing pseudotumor cerebri including certain tetracyclines. Increased risk of vit A hepatotoxicity w/ chronic excessive alcohol consumption. Decreased serum conc & increased seizure risk of anticonvulsants eg, phenytoin, fosphenytoin, phenobarb, primidone. Additive platelet function inhibition w/ antiplatelets eg, aspirin. Reduced folic acid levels w/ high dose aspirin. Folate, pyridoxine & vit D deficiencies w/ phenytoin, carbamazepine, phenobarb, valproate. Decreased vit D levels w/ efavirenz & zidovudine. Decreased formation of active vit D metabolite w/ PIs. Inhibited hematological response to vit B
12 therapy w/ chloramphenicol. Increased risk of Fe-induced cardiac failure w/ deferoxamine. Pyridoxine deficiency w/ ethionamide; pyridoxine antagonists, including cycloserine, hydralazine, INH, penicillamine, phenelzine; theophylline. Increased cytotoxicity w/ fluoropyrimidines eg, 5-fluorouracil, capecitabine, tegafur. Reduced effectiveness w/ folate antagonists eg, MTX, sulfasalazine, pyrimethamine, triamterene, trimethoprim & high doses of tea catechins. Decreased antimetabolite effects of folate antimetabolites eg, MTX, raltitrexed. Increased risk of toxicity w/ retinoids, including bexarotene. Enhanced anticoagulant effect of vit K antagonists (eg, warfarin) by vit E. Increased unbound fraction of drugs known to bind to α
1-acid glycoprotein eg, propranolol, prazosin. Enhance amiodarone-induced photosensitivity. Increased bleeding risk w/ agents w/ anticoagulant effects eg, abciximab, clopidogrel, heparin, warfarin. Inhibited metabolism w/ carbamazepine. Inhibited chemotherapy activity by antioxidant effects of high doses vit E. Decreased insulin sensitivity of insulin & antidiabetics. Reduced hematological response to Fe in anemic patients. Breakthrough bleeding & contraceptive failure w/ OCs. Increased metabolism/lower serum levels & reduced effect of phenobarb. Lower serum levels by phenytoin, fosphenytoin. Increased primidone levels.