Clin Infect Dis. 2015 Jan 15;60(2):275-8. doi: 10.1093/cid/ciu798. Epub 2014 Oct 13.

Breastfeeding while taking lamivudine or tenofovir disoproxil fumarate: a review of the evidence.
Ehrhardt S, Xie C, Guo N, Nelson K, Thio CL.

Lamivudine and tenofovir disoproxil fumarate (TDF) are both active against hepatitis B virus (HBV). Due to its potency, high genetic barrier to resistance, and safety during pregnancy, TDF may be useful to prevent HBV transmission from mother to child, which is the leading cause of transmission globally. Despite the safety record of lamivudine and TDF in pregnancy, the labels for both of these drugs recommend against their use during breastfeeding. In this review, we discuss the data regarding lamivudine and TDF use during pregnancy and breastfeeding and find that the exposure to the drug is lower from breastfeeding than from in utero exposure. Thus, the data do not support the contraindication to their use during breastfeeding.