Induced tissue desaturation w/ aspirin, nicotine, Fe, phenytoin, tetracycline, estrogen from OCs, & some appetite suppresants & anticonvulsant drugs. Reduced absorption & decreased urinary excretion w/ aspirin. Reduced serum levels w/ OCs. May cause unexpected renal tubular reabsorption of acidic drugs & decreased reabsorption of basic drugs. May reduce response to oral anticoagulants. May decrease plasma conc of fluphenazine. May worsen Fe toxicity to the heart w/ desferrioxamine.