Thiamine HCl: Not to be used w/ substances that yield alkaline soln eg, citrates, barbiturates, carbonates, erythromycin lactobionate IV. Nicotinamide: Increased risk of myopathy or rhabdomyolysis w/ HMG-CoA reductase inhibitors eg, atorvastatin, cerivastatin, fluvastatin, lovastatin, pravastatin, rosuvastatin, simvastatin. Decreased absorption w/ cholestyramine & colestipol. Flushing & dizziness w/ nicotine. Increased flushing & pruritus w/ alcohol. False-positive reactions for urinary glucose & false elevations of catecholamine levels w/ niacin may occur. Lysine HCl: Increased need for pyridoxine w/ cycloserine, INH, hydralazine, OCs, penicillamine. Decreased levodopa effect. May decrease phenytoin serum levels. False-positive urobilinogen spot test may occur. Cyanocobalamin: Absorption may be reduced w/ long-term aminosalicylic acid therapy & be inhibited by prolonged oral cimetidine. Reduced available amounts for serum & body stores w/ ascorbic acid. Decreased hematologic response w/ chloramphenicol. Bioavailability may be decreased w/ colestipol. Decreased absorption w/ omeprazole & ranitidine.