Population pharmacokinetics of levofloxacin in breastmilk in patients with rifampicin-resistant tuberculosis

Levofloxacin is a widely used antibiotic included in rifampicin-resistant tuberculosis (RR-TB) treatment. Data describing levofloxacin concentrations in breastmilk and infant exposure are limited. We analysed data from two South African studies of breastfeeding women receiving levofloxacin (750-1000 mg daily) for RR-TB. Plasma and breastmilk samples were collected over eight hours, ≥5 weeks postpartum. A single plasma sample was obtained from breastfed infants. Twenty women contributed paired plasma-breastmilk samples, 15 plasma concentrations from breastfed infants were available. Using nonlinear mixed-effects modelling, levofloxacin equilibrated rapidly between plasma and breastmilk (7.50 min half-life; 95% CI: 3.89-11.5), with a breastmilk: plasma ratio of 1.46 (95% CI: 1.40-1.52). The relative infant dose through breastfeeding was 6-8% of the recommended 15-20 mg/kg/day adult and paediatric dose, confirmed by low (but detectable) concentrations in some infants. It is unclear whether these low infant concentrations may be prophylactic or instead contribute to the development of drug resistance.