A new study offers some of the first data on how the COVID-19 drug nirmatrelvir/ritonavir (Paxlovid) behaves in breastfeeding women. The research included 8 healthy lactating women who took the standard 300 mg/100 mg dose. Researchers measured drug levels in their breast milk and blood.
The results showed that concentrations of both nirmatrelvir and ritonavir in breast milk were consistently lower than in the mother's blood. Based on these levels, the estimated daily dose an infant would receive through breast milk was very small: about 1.8% of the mother's dose for nirmatrelvir and 0.19% for ritonavir. The drug was well tolerated, with only mild to moderate side effects and no serious adverse events.
However, this is a very early Phase 1 study with only 8 participants. Breastfeeding women were excluded from larger clinical trials, so data in this population are limited. The study provides initial reassurance, but more research is needed to fully understand the risks and benefits for nursing mothers and their infants.