May decrease absorption of tetracycline & Fe; take tetracycline 1 hr before or 2 hr after antacids & 2 hr before or 3 hr after Fe-containing prep. May decrease absorption of oral digoxin or indomethacin, INH, quinolones (eg, ciprofloxacin, ofloxacin), ketoconazole. May increase urinary excretion due to changes in urine pH & decrease blood conc of salicylates eg, aspirin. Increase in urine pH may decrease excretion of weakly basic drugs (eg, quinidine, chlorpromazine, propranolol, diazepam) & increase excretion of weakly acidic drugs (eg, phenytoin, pentobarbital, warfarin). May increase absorption of dicumarol, diazepam & pseudoephedrine. May decrease the rate of chlordiazepoxide absorption. May reduce the bioavailability of biphosphonates (eg, alendronate, etidronate, risedronate).