From the Guidelines
Functional B6 deficiency can be caused by medications such as isoniazid (INH), hydralazine, penicillamine, and certain anticonvulsants, as well as conditions like alcoholism, kidney disease, and autoimmune disorders. Medications that commonly cause functional B6 deficiency include:
- Isoniazid (INH), used for tuberculosis treatment, which requires supplementation with pyridoxine (typically 25-100 mg daily) to prevent neuropathy, as recommended by the official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America clinical practice guidelines 1.
- Hydralazine, prescribed for hypertension
- Penicillamine, used for Wilson's disease and rheumatoid arthritis
- Certain anticonvulsants like phenytoin, carbamazepine, and phenobarbital These drugs interfere with B6 metabolism by inhibiting pyridoxal kinase or forming complexes with pyridoxal phosphate, the active form of B6. Medical conditions that can lead to functional B6 deficiency include:
- Alcoholism
- Kidney disease
- Autoimmune disorders
- Certain genetic disorders affecting B6 metabolism like pyridoxine-dependent epilepsy Symptoms of functional B6 deficiency may include:
- Peripheral neuropathy
- Dermatitis
- Glossitis
- Depression
- Confusion
- Anemia For patients taking these medications, supplementation with pyridoxine is often recommended, though dosing should be individualized, with recent guidelines suggesting doses of 50-100 mg for one to two weeks for deficiency resulting from chronic poor dietary intake 1. It's also important to note that excessive B6 supplementation itself can cause neuropathy, so appropriate dosing is crucial, and high doses of pyridoxine should be part of the therapy in cases of isoniazide overdose or glycol poisoning, with a recommended dose of 5 g (1 g of pyridoxine for each gram of isoniazid ingested, then 1 g IM or IV every 30 min up to a maximum of 5 g) 1.
From the FDA Drug Label
Pyridoxine (vitamin B6) deficiency is sometimes observed in adults with high doses of isoniazid and is considered probably due to its competition with pyridoxal phosphate for the enzyme apotryptophanase. Metabolic and Endocrine Reactions Pyridoxine deficiency, pellagra, hyperglycemia, metabolic acidosis, and gynecomastia.
Medications that may cause functional B6 deficiency:
- Isoniazid (high doses) 2 2 Conditions that may contribute to functional B6 deficiency:
- Malnutrition
- Alcoholism
- Diabetes
- High doses of isoniazid therapy 2 2
From the Research
Medications or Conditions Causing Functional B6 Deficiency
- Isoniazid (INH) therapy can cause a functional B6 deficiency, as it competitively inhibits the action of pyridoxine in metabolic functions, leading to peripheral neuropathy 3.
- Certain disorders affecting vitamin B6 metabolism, such as pyridox(am)ine phosphate oxidase deficiency, hypophosphatasia, and glycosylphosphatidylinositol anchor synthesis defects, can lead to PLP deficiency and manifest as B6-responsive epilepsy 4.
- High levels of vitamin B6 intake, usually through nutritional supplements, can lead to the development of peripheral neuropathy, particularly a predominantly sensory neuropathy of the axonal type 5.
Conditions Associated with High B6 Levels
- Peripheral neuropathy, particularly a predominantly sensory neuropathy of the axonal type, has been associated with high vitamin B6 levels 5.
- Certain diseases, such as impaired cognitive function, Alzheimer's disease, cardiovascular disease, and different types of cancer, have been linked to suboptimal vitamin B6 status, although the exact mechanisms are not fully understood 6.