Vitamin B6 : Safety and Interactions

by MedlinePlus

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Safety

Allergies

Avoid vitamin B6 products if you are sensitive or allergic to any of their ingredients.

Side Effects and Warnings

Some individuals seem to be particularly sensitive to vitamin B6 and may have problems at lower doses. Overall, pyridoxine is generally considered safe in adults and children when used appropriately at recommended doses. Avoid excessive dosing.

Dermatologic: Acne, skin reactions, allergic reactions, and photosensitivity have been reported. High-dose pyridoxine (80mg/day) and vitamin B12 (20micrograms/day) has been associated with rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Injected/IV pyridoxine can cause burning or stinging at the injection site.

Gastrointestinal: Nausea, vomiting, abdominal pain, loss of appetite, and increased liver function test results (serum aspartate transaminase (AST, SGOT)) have been reported. There is some preliminary concern that long-term dietary pyridoxine intake in small amounts ranging from 3.56-6.59mg per day may increase the risk of developing ulcerative colitis.

Neurologic: Headache, paresthesia, somnolence, and sensory neuropathy have been reported. Long-term treatment of two months or longer with 50-2000mg per day can cause peripheral sensory neuropathy that is usually reversible or neuropathy syndromes. Doses exceeding 1000mg per day or total doses of 1000 grams or more pose the most risk, although neuropathy can occur with lower daily or total doses as well. Some researchers recommend pyridoxal phosphate to avoid pyridoxine neuropathy, but its safety is unknown. Pyridoxine neuropathy is characterized by numbness and impairment of the sense of position and vibration of the distal limbs, and a gradual progressive sensory ataxia. The syndrome is usually reversible with discontinuation of pyridoxine at the first appearance of neurologic symptoms. Residual symptoms have been reported in patients taking more than 2 grams per day for extended periods. Daily doses of 100mg or less are unlikely to cause problems.

Miscellaneous: Breast soreness or enlargement, decreased serum folic acid levels, seizures after large doses, hypotonia and respiratory distress in infants have also been reported.

Pregnancy and Breastfeeding

Pregnancy: Vitamin B6 is likely safe when used orally in doses not exceeding the recommended dietary allowance (RDA). The RDA for pregnant women is 1.9mg per day. Vitamin B6 is possibly safe when used orally and appropriately in amounts exceeding the recommended dietary allowance. For relief of severe nausea in early pregnancy, 30-75mg/day has been used. A special sustained-release multi-ingredient product providing pyridoxine 75mg per day is FDA-approved for use in pregnancy. However, it should not be used long-term or without medical supervision and close monitoring or in more excessive doses. There is some concern that high-dose maternal pyridoxine can cause neonatal seizures.

Breastfeeding: Vitamin B6 is likely safe when used orally in doses not exceeding the recommended dietary allowance (RDA). The RDA in lactating women is 2mg per day. There is insufficient reliable information about the safety of pyridoxine when used in higher doses in lactating women. Because most lactating women do not consume the RDA of vitamin B6 in their normal diets and do not provide totally breast-fed infants with the RDA of this vitamin, doses as high as 4mg per day of vitamin B6 may be recommended although benefits have not been well proven.

Interactions

Interactions with Drugs

Amiodarone (Cordarone®): Preliminary research suggests that pyridoxine could exacerbate amiodarone-induced photosensitivity. Other research suggests a protective effect. Due to conflicting information, a firm conclusion cannot be drawn at this time but monitoring may be warranted.

Antibiotics: Destruction of normal gastrointestinal flora by antibiotics can cause decreased production of the B vitamins. Clinical significance is unknown.

Cycloserine (Seromycin®): Cycloserine is an antibiotic that may cause anemia or peripheral neuritis by acting as a pyridoxine antagonist or increasing renal excretion of pyridoxine. Requirements for pyridoxine may be increased in patients receiving cycloserine. 100-300mg may be taken daily in divided doses to prevent these seizures if recommended by a qualified healthcare provider.

Estrogens and birth control pills: Use of estrogens and estrogen-containing oral contraceptives can interfere with pyridoxine metabolism, reducing serum pyridoxine levels. The need for pyridoxine supplementation has not been adequately studied. .

Hydralazine (Apresoline®): Hydralazine can increase pyridoxine requirements. The need for pyridoxine supplementation has not been adequately studied.

Isoniazid (INH, Rifamate®): Isoniazid can increase pyridoxine requirements. Patients receiving more than 10mg/kg/day of INH should be supplemented with 50-100mg of pyridoxine per day.

Levodopa (Sinemet®): Pyridoxine enhances the metabolism of levodopa, reducing its anti-parkinsonism effects. Carbidopa and levodopa used together may avoid this interaction.

Penicillamine (Cuprimine®, Depen®): Penicillamine can increase pyridoxine requirements.

Phenobarbital (Luminal®): Preliminary data suggests that pyridoxine 200mg per day can reduce plasma levels of phenobarbital, possibly by increasing metabolism. Patients taking phenobarbital should avoid high doses of pyridoxine.

Phenytoin (Dilantin®): Preliminary data suggests that pyridoxine 200mg per day can reduce plasma levels of phenytoin, possibly by increasing metabolism. Patients taking phenytoin should avoid high doses of pyridoxine.

Theophylline (Theo-Dur®): Theophylline, a medication used for asthma, interferes with pyridoxine metabolism. Study results of supplemental pyridoxine in these patients are inconclusive.

Interactions with Herbs and Dietary Supplements

Estrogenic herbs and supplements: Theoretically, herbs and supplements with estrogen- like activity may interact with pyridoxine. The need for pyridoxine supplementation has not been adequately studied.

Interactions with Labs

Homocysteine: High doses of folic acid, vitamin B6, and vitamin B12 normalize homocysteine values in the majority of peritoneal dialysis patients. This treatment may be important in reducing cardiovascular morbidity and mortality.

Liver function tests: Serum aspartate transaminase (AST, SGOT) may be elevated.

Phenobarbital (Luminal®): Preliminary data suggests that pyridoxine 200mg per day can reduce plasma levels of phenobarbital, possibly by increasing metabolism.

Phenytoin (Dilantin®): Preliminary data suggests that pyridoxine 200mg per day can reduce plasma levels of phenytoin, possibly by increasing metabolism.

Theophylline (Theo-Dur®): Theophylline interferes with pyridoxine metabolism.

Urobilinogen: Pyridoxine can cause a false positive result in the spot test with Ehrlich's reagent.

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