Table 3:

B vitamins and possible risk factors and drug interaction

Vitamin	Risk factors for deficiency	Mechanism
Thiamine (B1)	–Diuretics 15 –Fluorouracil (5-fluorouracil) 15 –High carb diet 3	–Increases urinary loss 15 –Increases thiamine metabolism –Aerobic glucose breakdown consumes thiamine 3
Riboflavin (B2)	–Long-term barbiturate use 5,16 –Tricyclic antidepressant and contraceptive pills 16 –Tetracyclines 16	–Impairs riboflavin function 5 –Decreases riboflavin absorption 16 –Riboflavin decreases tetracycline absorption 16
Niacin (B3)	–Alcohol 1 –Nicotine patches –Azathioprine, 6-mercaptopurine, or 5-fluorouracil 6 –Isoniazid 2,6,7	–Decreases niacin absorption 1 –Worsens flushing. –Decreases tryptophan conversion to niacin 6,7 –Decreases tryptophan production 2,6,7
Pantothenic acid (B5)	–Antibiotics (especially tetracyclines), cholinesterase inhibitors, and memantine 8,17	–Vitamin B5 interferes with the absorption and effectiveness of these drugs 17
Pyridoxine, pyridoxal, pyridoxamine (B6)	–Cycloserine (tuberculosis treatment) –Antiepileptic drugs (valproic acid, carbamazepine, and phenytoin) 9,18 –INH 9,19,20	–Increases urine excretion of B6 –Increases the catabolism of B6 9,18 –Inhibits the action of B6 9,18
Biotin (B7)	–Anticonvulsants 12 –Troponin –Thyroid function tests –25-hydroxy vitamin D29	–Increases biotin metabolism 2 –False low results –False hyperthyroid results –False positive or abnormal results 21
Folic acid, folate (B9)	–Antiepileptic drugs, including gabapentin –Methotrexate –Adrucil, Hydrea, Daraprim, Bactrim, and Septra –Metformin and cholestyramine 2,22,23	–Impairs absorption and increases metabolism –Causes functional deficiency –Affects folate metabolism –Decreases absorption 2,22,23
Cobalamin (B12)	–Metformin, antiacid, aminoglycoside antibiotics, and colchicine 14	–Decreases B12 absorption 14

INH = brand name of isoniazid; Adrucil = brand name of 5-fluorouracil; Hydrea = brand name of hydroxyurea; Daraprim = brand name of pyrimethamine; Bactrim = brand name of trimethoprim/sulfamethoxazole; and Septra = brand name of trimethoprim/sulfamethoxazole.