To determine milk to plasma (M: P) ratios and infant dose (absolute and relative) for isoniazid in lactating women on antituberculosis therapy.METHODS
Concentrations of isoniazid in plasma and milk were measured in exclusively breast feeding women taking 300 mg day−1 as treatment for tuberculosis.RESULTS
Peak plasma and milk concentrations of isoniazid were observed at 1 h. A mean M: PAUC value of 0.89 (95% CI 0.7, 1.1) was calculated for isoniazid from seven women over 24 h. The mean absolute infant dose was estimated to be 89.9 μg kg day−1 (95% CI 65.6, 114) and the relative infant dose was 1.2% of the weight adjusted maternal dose.CONCLUSIONS
The mean relative dose of isoniazid (1.2%) transmitted to the infant via breast milk is below the 10% notional level of concern. These data suggest that isoniazid therapy is safe during breastfeeding.