From the Guidelines
The recommended dosage of vitamin B6 (pyridoxine) for patients taking isoniazid is 25-50 mg daily. This supplementation is essential for preventing peripheral neuropathy, which is a common side effect of isoniazid therapy, as noted in the official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America clinical practice guidelines: treatment of drug-susceptible tuberculosis 1. Isoniazid interferes with vitamin B6 metabolism by forming hydrazones with pyridoxal phosphate, the active form of vitamin B6, thereby reducing its availability for normal neurological function.
Key Considerations
- Higher doses of vitamin B6 (100 mg daily) may be appropriate for individuals at increased risk of developing neuropathy, including those with diabetes, HIV infection, alcoholism, malnutrition, pregnancy, or renal failure, as recommended by experts 1.
- The supplementation should begin at the same time as isoniazid therapy and continue throughout the entire course of treatment.
- If peripheral neuropathy symptoms develop despite prophylactic B6 supplementation, the dosage may need to be increased.
- Vitamin B6 is generally well-tolerated, though very high doses (over 200 mg daily for extended periods) should be avoided as they may paradoxically cause neuropathy.
Recent Guidance
The most recent guidance from 2022 also supports the use of pyridoxine (vitamin B6) at a dose of 25–50 mg/day with isoniazid to all patients, as part of a 4-month rifapentine-moxifloxacin regimen for the treatment of drug-susceptible pulmonary tuberculosis 1. This emphasizes the ongoing importance of vitamin B6 supplementation in the prevention of isoniazid-induced neuropathy.
From the FDA Drug Label
Concomitant administration of pyridoxine (B6) is recommended in malnourished and in those predisposed to neuropathy (e.g., alcoholics and diabetics). The recommended dosage of vitamin B6 is not explicitly stated in the drug label for isoniazid.
- Key point: The label only mentions that concomitant administration of pyridoxine (B6) is recommended in certain cases, but does not provide a specific dosage. 2
From the Research
Vitamin B6 Dosage for Isoniazid
- The recommended dosage of vitamin B6 for isoniazid is not explicitly stated in the provided studies, but it can be inferred that a daily dose of 50 mg is considered safe and potentially effective in preventing peripheral neuropathy 3, 4.
- High doses of vitamin B6, above 50 mg/day, may be neurotoxic and provoke a progressive sensory neuronopathy, as seen in a case study where a patient developed sensory neuropathy after taking 1250-1750 mg/day of pyridoxine for 20 years 3.
- The currently recommended daily allowance of vitamin B6 is 1.5-2 mg/day, but this may not be sufficient for patients with comorbid conditions or those taking isoniazid, as it may result in inadequate vitamin B6 status 4.
- PLP-based supplements are preferred over pyridoxine supplements due to their minimal neurotoxicity, and weekly administration of 50-100 mg is recommended to maintain a stable serum PLP level between 30 and 60 nmol/L or 7.4 and 15 μg/L 4.
- It is essential to monitor plasma B6 levels and adjust the dosage accordingly to prevent neurotoxicity, as elevated levels of pyridoxine can be associated with neuropathy 4, 5.