Substances in food (eg, sulfite, caffeine) may inactivate thiamine. Thiamine may enhance the effect of neuromuscular blocking agents. Probenecid may inhibit riboflavin absorption & renal tubular secretion. OC agents may result in decreased serum levels of riboflavin; may increase vit B
6 requirements. Risk for lower plasma Zn conc in women who are taking folic acid supplements, especially if are current or former users of OCs. Chronic & excessive use of alcoholic beverages can result in vit B
6 deficiency. Metformin may decrease the absorption of vit B
12. Concomitant use w/ digoxin or any cardiac glycosides. Broad-spectrum antibiotics may sterilize the bowel & decrease vit K
1 contribution to the body. Cephalosporins containing side chains of N-methylthiotetrazole or methylthiadizole can cause vit K deficiency & hypoprothrombinemia. Vit K
1 can antagonize the effect of warfarin. Antibiotics may decrease the biotin contribution to the body.