CONTRAINDICATIONS, PRECAUTIONS, ADVERSE REACTIONS

Pre- and postnatal vitamin/mineral supplements typically deliver vitamin B₆ (as pyridoxine) at a dose of between 2 to 20 milligrams daily. Pregnant women and nursing mothers should avoid doses of vitamin B₆ greater than these doses, unless higher doses are prescribed by their physicians.

Those who are being treated with levodopa without concurrently taking carbidopa should avoid doses of vitamin B₆ of 5 milligrams or greater daily.

The use of vitamin B₆ for the treatment of vitamin B₆ deficiency, for the prophylaxis of isoniazid-induced peripheral neuropathy, for the treatment of vitamin B₆-dependency disorders (see Indications) or for the treatment of any other medical condition requires medical supervision.

ADVERSE REACTIONS

Doses of vitamin B₆, typically in the form of pyridoxine, of up to 200 milligrams daily are generally well tolerated. One report showed severe sensory neuropathy in seven adults after pyridoxine intakes that started at 50 to 100 milligrams/day and were steadily increased to 2 to 6 grams/day over 2 to 40 months. None of the subjects in the report showed sensory neuropathy at doses of pyridoxine of less than 2 grams/day. There is one report of a woman who had been taking 200 milligrams/day of pyridoxine for 2 years without showing sensory neuropathy who developed sensory neuropathy after she increased her pyridoxine dose to 500 milligrams/day. There are rare reports of sensory neuropathy occurring at pyridoxine doses in the range of 100 to 200 milligrams/day. The Food and Nutrition Board of the Institute of Medicine of the U.S. National Academy of Sciences has concluded that reports and studies showing sensory neuropathy at doses of pyridoxine less than 200 milligrams/day are weak and inconsistent, with the weight of evidence indicating that sensory neuropathy is unlikely to occur in adults taking pyridoxine at doses less than 500 milligrams/day.

Other adverse reactions reported with high doses of pyridoxine, include nausea, vomiting, abdominal pain, loss of appetite and breast soreness. Rare cases of pyridoxine-induced photosensitivity have been reported.

INTERACTIONS

DRUGS

Amiodarone: Concomitant use of vitamin B₆ and amiodarone may enhance amiodarone-induced photosensitivity reactions. Doses of vitamin B₆ greater than 5-10 milligrams/day should be avoided by those taking amiodarone.

Carbamazepine: Chronic use of carbamazepine may result in a significant decrease in plasma pyridoxal 5'-phosphate levels.

Cycloserine: Cycloserine may react with pyridoxal 5'-phosphate to form a metabolically inactive oxime, which may result in a functional vitamin B₆ deficiency.

Ethionamide: The use of ethionamide may increase vitamin B₆ requirements.

Fosphenytoin: High doses of vitamin B₆ may lower plasma levels of phenytoin. Fosphenytoin is a prodrug of phenytoin.

Hydralazine: The use of hydralazine may increase vitamin B₆ requirements.

Isoniazid: (isonicotinic acid, INH). Isoniazid reacts with pyridoxal 5'-phosphate to form a metabolically inactive hydrazone, which may result in functional vitamin B₆ deficiency.

Levodopa: Concomitant use of levodopa and vitamin B₆ in doses of 5 milligrams or more daily may reverse the therapeutic effects of levodopa. Vitamin B₆ does not reverse the therapeutic effects of levodopa if levodopa is taken concurrently with the levodopa decarboxylase inhibitor carbidopa. Levodopa is typically administered as a combination product with carbidopa.

Oral contraceptives: The use of oral contraceptives may increase vitamin B₆ requirements. This was more the case with the older oral contraceptive agents with high-dose estrogen/progestin. It appears to be less the case with the newer low-dose estrogen/progestin products.

Penicillamine: Penicillamine may react with pyridoxal 5'-phosphate to form a metabolically inactive thiazolidine, which may result in a functional vitamin B₆ deficiency.

Phenelzine: Phenelzine may react with pyridoxal 5'-phosphate to yield a metabolically inactive hydrazone compound.

Phenobarbital: High doses of vitamin B₆ may lower plasma levels of phenobarbital.

Phenytoin: High doses of vitamin B₆ may lower plasma levels of phenytoin.

Theophylline: Theophylline may react with pyridoxal 5'-phosphate leading to low plasma levels of the coenzyme. This may increase the risk of theophylline-induced seizures.

Valproic acid: Chronic use of valproic acid may result in a significant decrease in plasma pyridoxal 5'-phosphate levels.

FOODS

Alcoholic beverages: Alcohol may increase the catabolism of pyridoxal 5'-phosphate. Chronic and excessive use of alcoholic beverages can result in vitamin B₆ deficiency.

OVERDOSAGE

No reports.

DOSAGE AND ADMINISTRATION

Vitamin B₆ is available in nutritional supplements principally in the form of pyridoxine hydrochloride. Pyridoxal 5'-phosphate is also available as a nutritional supplement. Pyridoxine hydrochloride is available in multivitamin and multivitamin/multimineral products as well as products that, in addition to vitamins and minerals, contain other nutritional substances. Single ingredient pyridoxine products are also available. Some products are available which contain mixtures of pyridoxine hydrochloride and pyridoxal 5'-phosphate. Typical doses of pyridoxine used for nutritional supplementation range from 2 to 20 milligrams/day.

Those who use pyridoxine for the management of premenstrual syndrome, typically use doses ranging from 50 to 100 milligrams/day. Those who use pyridoxine for the management of carpal tunnel syndrome, typically use doses ranging from 100 to 200 milligrams/day.

The Food and Nutrition Board of the Institute of Medicine of the National Academy of Sciences has recommended the following Dietary Reference Intakes (DRI) for vitamin B₆:

HOW SUPPLIED

Vitamin B₆ is available in the following forms and strengths for OTC use:

Capsules � 150 mg, 500 mg

Enteric Coated Tablets � 20 mg

Tablets � 10 mg, 25 mg, 32.5 mg, 50 mg, 100 mg, 250 mg, 500 mg

Tablets Extended Release � 200 mg

Vitamin B₆ is available in the following forms and strengths for Rx use:

Injection � 100 mg/mL

LITERATURE

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Aybak M, Sermet A, Ayylidiz MO, Karakilcik AZ. Effect of oral pyridoxine hydrochloride supplementation on arterial blood pressure in patients with essential hypertension. Arzneimittelforschung. 1995; 45:1271-1273.

Bender DA. Non-nutritional uses of vitamin B₆. Br J Nutrition. 1999; 81:7-20.

Bendich A, Cohen M. Vitamin B₆ safety issues. Ann NY Acad Sci. 1990; 585:321-330.

Bernstein AL. Vitamin B₆ in clinical neurology. Ann NY Acad Sci. 1990; 585:250-260.

Bernstein AL, Dinesen JS. Brief communication: effect of pharmacologic doses of vitamin B₆ on carpal tunnel syndrome, electroencephalographic results, and pain. J Am Coll Nutr. 1993; 12:73-76.

Bilski P, Li MY, Ehrenshaft M, et al. Vitamin B₆ (pyridoxine) and its derivatives are efficient singlet oxygen quenchers and potential fungal antioxidants. Photochem Photobiol. 2000; 71:129-134.

Chang S-J. Vitamin B₆ protects vascular endothelial injury by activated platelets. Nutr Res. 1999; 19:1613-1624.

Dakshinamurti, K, ed. Vitamin B₆. New York, NY: The New York Academy of Sciences; 1990.

Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B₆, Folate, Vitamin B₁₂, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 1998; 150-195.

DiSorbo DM, Wagner R Jr, Nathanson L. In vivo and in vitro inhibition of B₁₆ melanoma growth by vitamin B₆. Nutr Cancer. 1985; 7:43-52.

Ellis J, Folkers K, Watanabe T, et al. Clinical results of a cross-over treatment with pyridoxine and placebo of the carpal tunnel syndrome. Am J Clin Nutr. 1979; 32:2040-2046.

Ellis JM, McCully KS. Prevention of myocardial infarction by vitamin B₆. Res Commun Mol Pathol Pharmacol. 1995; 89:208-220.

Franzblau A, Rock CL, Werner RA, et al. The relationship of vitamin B₆ status to median nerve function and carpal tunnel syndrome among active industrial workers. J Occup Environ Med. 1996; 38:485-491.

Gregory JF III. Nutritional properties and significance of vitamin glycosides. Annu Rev Nutr. 1998; 18:277-296.

Gridley DS, Schultz TD, Stickney DR, Slater JM. In vivo and in vitro stimulation of cell-mediated immunity by vitamin B₆. Nutr Res. 1988; 8:201-207.

Guilarte TR. Vitamin B₆ and cognitive development: recent research findings from human and animal studies. Nutr Rev. 1993; 51:193-198.

Khatami M. Role of pyridoxal phosphate/pyridoxine in diabetes. Inhibition of nonenzymatic glycosylation. Ann NY Acad Sci. 1990; 585:502-504.

Laso Guzman FJ, Gonzalez-Buitrago JM, de Arriba F, et al. Carpal tunnel syndrome and vitamin B₆. Klin Wochenschr. 1989; 67:38-41.

Leklem JE. Vitamin B₆. In: Shils ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9^th ed. Baltimore, MD: Williams and Wilkins; 1999; 413-421.

Maksymowych AB, Robertson NM, Litwack G. Efficacy of pyridoxal treatment in controlling the growth of melanomas in cell culture and an animal pilot study. Anticancer Research. 1993; 13:1925-1937.

Okada H, Moriwaki K, Kanno Y, et al. Vitamin B₆ supplementation can improve peripheral polyneuropathy in patients with chronic renal failure on high-flux haemodialysis and human recombinant erythropoietin. Nephrol Dial Transplant. 2000; 15:1410-1413.

Rall LC, Meydani SN. Vitamin B₆ and immune competence. Nutr Rev. 1993; 51:217-225.

Rimland B, Calloway E, Dreyfus P. The effects of high doses of vitamin B₆ on autistic children: a double-blind crossover study. Am J Psychiatry. 1978; 135:472-475.

Schaumburg H, Kaplan J, Windebank A, et al. Sensory neuropathy from pyridoxine abuse. N Engl J Med. 1983; 309:445-448.

Schneider G, Kàck H, Lindquist Y. The manifold of vitamin B₆ dependent enzymes. Structure. 2000; 8:R1-R6.

Sermet A, Aybak M, Ulak G, et al. Effect of oral pyridoxine hydrochloride supplementation on in vitro platelet sensitivity to different agonists. Arzneimittelforschung. 1995; 45:19-21.

Seto T, Inada H, Kobayashi N, et al. [Depression of serum pyridoxal levels in theophylline-related seizures]. [Article in Japanese]. No To Hattatsu. 2000; 32:295-300.

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

Shimizu T, Maeda S, Mochizuki H, et al. Theophylline attenuates circulating vitamin B₆ levels in children with asthma. Pharmacology. 1994; 49:392-397.

Spooner GR, Desai HB, Angel JF, et al. Using pyridoxine to treat carpal tunnel syndrome. Randomized control trial. Can Fam Physician. 1993; 39:2122-2127.

Stern F, Berner YN, Polyak Z, et al. [Nutritional status and vitamin B₆ supplementation in the institutionalized elderly]. [Article in Hebrew]. Harefuah. 2000; 139:97-102,167,166.

Stransky M, Rubin A, Lava NS, Lazaro RP. Treatment of carpal tunnel syndrome with vitamin B₆: a double-blind study. South Med J. 1989; 82:841-842.

Ubbink JB, Hayward Vermaak WJ, Delport R, Serfontein WJ. The relationship between vitamin B₆ metabolism, asthma, and theophylline therapy. Ann NY Acad Sci. 1990; 585:285-294.

Wyatt KM, Dimmock PW, Jones PW, Shaughn O'Brien PM. Efficacy of vitamin B₆ in the treatment of premenstrual syndrome: systemic review. Br Med J. 1999; 318:1375-1381.

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