- Design
- Population pharmacokinetic modelling of trial data (IMPAACT 2001)
- Population
- Pregnant and postpartum women on weekly isoniazid–rifapentine, and their infants
- Primary outcome
- Breast milk-to-plasma ratio and relative infant dose
- Effect
- Milk:plasma 0.024 (rifapentine), 0.041 (metabolite); relative infant dose <1%
A model-based pharmacokinetic analysis in Clinical Pharmacology & Therapeutics (15 October) used data from IMPAACT 2001, which gave weekly isoniazid and rifapentine (3HP) to pregnant and postpartum women for tuberculosis prevention. Concentrations were measured in maternal plasma, breast milk, cord blood and infant plasma.
Rifapentine and its active metabolite equilibrated quickly into milk but at low levels — milk-to-plasma ratios of about 0.02 and 0.04. The estimated maximum relative infant dose was under 1%, well below the 10% often used as a threshold for concern. Rifapentine crossed the placenta and was measurable in newborns, at concentrations the authors judged unlikely to matter clinically.
Where 3HP is used for TB preventive therapy, these data support offering it to breastfeeding women rather than delaying treatment. Rifapentine remains a strong enzyme inducer, so maternal co-medications still need checking.
- Relative infant dose of rifapentine via breast milk was estimated at under 1%
- Breastfeeding need not delay 3HP preventive therapy
- Rifapentine crosses the placenta; newborn levels were judged clinically insignificant
- Check the mother's other medicines, including hormonal contraception and antiretrovirals, for induction
Why it matters
Uncertainty about lactation often delays TB preventive therapy in postpartum women.
Don't overread it
A pharmacokinetic model, not an infant safety outcome study.
The statistics, in plain English
Relative infant dose compares the infant's intake through milk with the mother's weight-adjusted dose; under 10% is generally considered compatible with breastfeeding, and this estimate is under 1%.
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