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  • Latent TB

    I have MS and had to have blood work before I can move forward with my new therapy. I tested positive for Tuberculosis. X-rays cleared me of active TB. I have latent TB and am being put on Isoniazid for 9 months along with B6. I’m still breastfeeding my 19 month old. Is there anything I need to watch for in him?

  • #2
    Isoniazid (INH) is an antimicrobial agent primarily used to treat tuberculosis. Following doses of 5 and 10 mg/kg, one report measured peak milk levels at 6 mg/L and 9 mg/L respectively.[1] Isoniazid was not measurable in the infant's serum but was detected in the urine of several infants. In another study, following a maternal dose of 300 mg of isoniazid, the concentration of isoniazid in milk peaked at 3 hours at 16.6 mg/L while the acetyl derivative (AcINH) was 3.76 mg/L.[2] The 24 hour excretion of INH in milk was estimated at 7 mg. The authors felt this dose was potentially hazardous to a breastfed infant.

    In a recent and well-done study in seven exclusively lactating women (at 33 days or steady state) who were receiving 300 mg isoniazid daily in a single dose (and rifampin and ethambutol) the mean (AUC) of isoniazid in plasma and milk was 18.4 µg/mL/24 hours and 14.4 µg/mL/24 hours respectively.[3] The mean milk/plasma ratio (AUC) was 0.89 and the calculated relative infant dose was 1.2%. In this nicely done study, peak levels are clearly evident at 1 hour and fall rapidly at 4 hours.

    I'd suggest the mom avoid breastfeeding for 2-4 hours following administration of INH to avoid the peak plasma concentrations at 2 hours.

    Observe infants for fatigue, weakness, anorexia, nausea, and vomiting in the breastfed infant (these are unlikely).

    Tom Hale Ph.d.

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