Thiamine deficiency w/ chronic use of loop diuretics. Substances in food (eg, sulfite, caffeine) may inactivate thiamine. Possible enhancement of neuromuscular blocking agents effect w/ thiamine. May inhibit riboflavin absorption & renal tubular secretion w/ probenecid. Decreased riboflavin serum levels; increased vit B
6 requirements w/ OCs. Risk for lower Zn plasma conc in women taking folic acid supplements especially those currently or former users of OCs. Vit B
6 deficiency w/ chronic & excessive use of alcoholic beverages. Decreased vit B
12 absorption w/ metformin. Folic acid may work synergistically w/ vit B
12 in lowering homocysteine levels. Concomitant use w/ digoxin or any cardiac glycoside. May precipitate cardiac arrhythmias w/ digoxin. May sterilize the bowel & decrease vit K
1 contribution to the body w/ broad-spectrum antibiotics. May cause vit K deficiency & hypoprothrombinemia w/ cephalosporins containing N-methylthiotetrazole or methylthiadizole side chains. Vit K
1 can antagonize the effect of warfarin. Decreased biotin contribution to the body w/ antibiotics.