Antituberculosis medications such as cycloserine and isoniazid (INH) reduce the pyridoxine blood levels and may lead to peripheral neuritis (Wada 1998). Supplementation with vitamin B6 during therapy with either of these medications prevents the development of both deficiency and peripheral neuropathy.

In one study, 13 stable patients on chronic hemodialysis received pyridoxine (5 mg/day) in combination with erythropoietin (EPO) (Mydlik et al. 1997). EPO therapy increased hemoglobin synthesis, which decreased erythrocyte pyridoxine status.The pyridoxine concentration in erythrocytes was restored by increasing the dose to 20 mg/day. Supplementation with pyridoxine may be warranted in EPO-treated patients.

Administration of vitamin B6 (50 to 150 mg/day) during treatment with 5-FU has been reported to reverse 5-FU-induced palmar-plantar erythrodysesthesia without any adverse effects or interruption of chemotherapy (Fabian et al. 1990). Palmar-plantar erythrodysesthesia, a skin condition that can make holding objects, driving, or walking painful, may occur in cancer patients undergoing continuous infusions of 5-FU.

In the presence of pyridoxine, the hypotensive effects of hydralazine are diminished (Vidrio 1990).

Vitamin B6 reduces the therapeutic effects of levodopa by increasing the intestinal metabolism of levodopa to dopamine (Awad 1984; Ebadi et al. 1982). The anti-Parkinson effect of levodopa is decreased as a result of the inability of dopamine to cross the blood brain barrier. This antagonistic interaction between pyridoxine and levodopa is more likely to occur at higher pyridoxine doses. It is suggested that pyridoxine supplements not be taken with levodopa.

There have been case reports of MAOIs such as tranylcypromine and phenelzine interfering with vitamin B6 and reducing blood levels of this nutrient (Harrison et al. 1983; Heller and Friedman 1983). MAOI-induced decreases in pyridoxine status have been associated with peripheral neuropathy and carpal tunnel syndrome, both of which respond well to pyridoxine supplementation.

Supplementation with vitamins B1, B2, and B6 (10 mg each) at the start of tricyclic antidepressant therapy improved cognitive functioning and depression ratings in 14 geriatric patients undergoing treatment with nortriptyline (Bell et al. 1992). B vitamins may augment the treatment of depression in elderly patients.

Oral contraceptives deplete vitamin B6 levels, possibly through induction of tryptophan oxidase (Bermond 1982; Prasad et al. 1976; Slap 1981). Side effects such as depression may be due to altered metabolism of vitamin B6 and other B vitamins (Kane 1976). Please refer to the depletions monograph on oral contraceptives for additional information.

In a study involving 144 rheumatoid arthritis patients treated with penicillamine (125 to 1000 mg/day), 17% developed vitamin B6 deficiency; however, there were no clinical signs of deficiency (Rumsby and Shepherd 1981). Chronic penicillamine therapy may warrant monitoring of pyridoxine status.

A study with 27 epileptic patients aged 15 to 54 who received phenobarbitone (90 mg/day phenobarbital) and diphenylhydantion (300 mg/day phenytoin) regularly for 3 to 32 years noted that serum levels of vitamin B6 and B12 were increased significantly relative to controls (Dastur and Dave 1987). Increased serum vitamin levels may be indicative of hepatic damage from anticonvulsant therapy. However, supplementation with vitamin B6 may decrease the pharmacologic effects of phenytoin (Hines Burnham et al 2000).

In one study, the bioavailability of tetracycline hydrochloride was reduced significantly by concomitant administration of vitamin B complex to healthy subjects (Omray 1981). Patients should be cautioned to take vitamin B complex supplements at different times from tetracycline.

Slow-release theophylline lowered serum vitamin B6 levels by 40% in 16 asthmatic children treated this medication for over a year (Shimizu et al. 1996).

Awad AG. Diet and drug interactions in the treatment of mental illness – a review. Can J Psychiatry. 1984;29:609-613.

Bell IR, Edman JS, Morrow FD, et al. Brief communication: Vitamin B1, B2, and B6 augmentation of tricyclic antidepressant treatment in geriatric depression with cognitive dysfunction. J Am Coll Nutr. 1992;11(2):159-163.

Dastur DK, Dave UP. Effect of prolonged anticonvulsant medication in epileptic patients: serum lipids, vitamins B6, B12, and folic acid, proteins, and fine structures of the liver. Epilepsia. 1987;28(2):147-159.

Ebadi M, Gessert CF, Al Sayegh A. Drug-pyridoxal phosphate interactions. Q Rev Drug Metab Drg Interact. 1982;4(4):289-331.

Fabian CJ, Molina R, Slavik M, Dahlberg S, Giri S, Stephens R. Pyridoxine therapy for palmar-plantar erythrodysesthesia associated with continuous 5-fluorouracil infusion. Invest New Drugs. 1990;8(1):57-63.

Hines Burnham, et al, eds. Drug Facts and Comparisons. St. Louis, MO:Facts and Comparisons; 2000:18.

Mydlik M, Derzsiova K, Zemberova E. Metabolism of vitamin B₆ and its requirement in chronic renal failure. Kidney Int. 1997;52:S56-S59.

Omray A. Evaluation of pharmacokinetic parameters of tetracylcine hydrochloride upon oral administration with vitamin C and vitamin B complex. Hindustan Antibiot Bull. 1981;23(VI):33-37.

Rumsby PC, Shepherd DM. The effect of penicillamine on vitamin B6 function in man. Biochem Pharmacol. 1981;30(22):3051-3053.

Shimizu T, Maeda S, Arakawa H, et al. Relation between theophylline and circulating vitamin levels in children with asthma. Pharmacol. 1996;53:384-389.

Vidrio H. Interaction with pyridoxal as a possible mechanism of hydralazine hypotension. J Cardiovasc Pharmacol. 1990;15(1):150-156.

Wada M. The adverse reactions of anti-tuberculosis drugs and its management [in Japanese]. Nippon Rinsho. 1998;56(12):3091-3095.

Harrison, W, Stewart J, Lovelace R, Quitkin F. Case report of carpal tunnel syndrome associated with tranylcypromine. Am J Psychiatry. 1983;140(9):1229-1230.

Heller CA, Friedman PA. Pyridoxine deficiency and peripheral neuropathy associated with long-term phenelzine therapy. Am J Med. 1983;75(5):887-888.

Bermond P. Therapy of side effects of oral contraceptive agents with vitamin B6. Acta Vitaminol Enzymol. 1982;4(1-2):45-54.

Prasad AS, Lei KY, Moghissi KS, et al. Effect of oral contraceptives on nutrients. III. Vitamins B6, B12, and folic acid. Am J Obstet Gynecol. 1976;125(8):1063-1069.

Slap GB. Oral contraceptives and depression: impact, prevalence and cause. J Adolesc Health Care. 1981;2(1):53-64.

Kane FJ. Evaluation of emotional reactions to oral contraceptive use. Am J Obstet Gynecol. 1976;126(8):968-972.