Pyridoxine Dosing for an 8.3 kg Infant on Cycloserine
Give 10–12.5 mg of pyridoxine daily for this 8.3 kg infant receiving cycloserine.
Dosing Rationale
Cycloserine, like isoniazid, interferes with vitamin B6 metabolism and requires prophylactic pyridoxine supplementation to prevent neurotoxicity, including seizures. 1
For infants and children on medications that deplete pyridoxine (such as cycloserine or isoniazid), the WHO advises avoiding vitamin B6 intake exceeding 1.0 mg/kg/day due to potential toxicity. 2
At 8.3 kg body weight, the maximum safe dose would be approximately 8.3 mg/day using the strict WHO threshold, but clinical practice for tuberculosis medications typically uses higher prophylactic doses. 2
Historical data from high-dose isoniazid therapy demonstrates that 6 mg daily of pyridoxine was fully effective in preventing peripheral neuropathy in adults receiving 12.5–15.2 mg/kg/day of isoniazid. 3
Scaling this pediatric dose proportionally: an 8.3 kg infant represents roughly 10–15% of adult body weight (assuming 60 kg adult), suggesting a dose range of 10–12.5 mg daily would provide equivalent prophylaxis while remaining well below toxicity thresholds. 4, 3
Safety Considerations
The therapeutic window is wide: prophylactic doses of 1.5–6 mg daily are considered safe in newborns, and toxicity only occurs with chronic intake exceeding 100–300 mg daily in adults. 4
For infants, toxicity concerns arise only at doses far exceeding 1 mg/kg/day chronically (>8.3 mg/day for this patient), but short-term prophylactic use at 10–12.5 mg/day remains within established safety margins for tuberculosis medication prophylaxis. 2, 3
Pyridoxine has been used acutely to manage cycloserine-induced seizures in emergency settings, demonstrating both its safety and necessity in this clinical context. 1
Practical Administration
Administer the dose enterally (orally) as a single daily dose, which can be given with or without food. 4
Monitor for signs of peripheral neuropathy (irritability, poor feeding, developmental regression) or seizure activity, though these are unlikely at prophylactic doses. 1
Critical Pitfall to Avoid
- Do not confuse prophylactic dosing (10–12.5 mg daily for this infant) with acute seizure management, which may require gram-for-gram replacement in cycloserine overdose scenarios—these are entirely different clinical situations. 4