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Fertility: Reproductive studies in animals have shown no effect on male or female fertility.
Pregnancy: The Antiretroviral Pregnancy Registry has received reports of over 11,000 exposures to lamivudine during pregnancy resulting in live birth, less than 1% of which were in patients with HBV. These consist of over 4,500 exposures during the first trimester, over 7,200 exposures during the second/third trimester and included 143 and 207 major birth defects respectively. The prevalence (95% CI) of defects in the first trimester was 3.1% (2.6, 3.7%) and in the second/third trimester, 2.9% (2.5, 3.3%). Among pregnant women in the reference population, the background rate of birth defects is 2.7%. Available human data from the Antiretroviral Pregnancy Registry does not show a significantly higher risk of major birth defects for lamivudine compared to the background rate. However, there are no adequate and well-controlled trials in pregnant women and the safe use of lamivudine in human pregnancy has not been established.
Studies in humans have confirmed that 3TC-HBV crosses the placenta.
Use in pregnancy should be considered only if the benefit outweighs the risk. Although the results of animal studies (see Pharmacology: Pharmacodynamics: Non-Clinical Information under Actions) are not always predictive of human response, there was no evidence of teratogenicity in animals but, findings in rabbits suggest a potential risk of early embryonic loss that was not observed in the rat. For patients who are being treated with 3TC-HBV and subsequently become pregnant consideration should be given to the possibility of a recurrence of hepatitis on discontinuation of 3TC-HBV (see Precautions).
Lactation: Following repeat oral administration of either 150 mg or 300 mg, lamivudine twice daily, lamivudine was excreted in human breast milk (0.5 to 8.2 micrograms/mL) at similar concentrations to those found in serum. In other studies, following repeat oral administration of 150 mg lamivudine twice daily the breast milk: maternal plasma ratio ranged between 0.6 and 3.3. Lamivudine median infant serum concentrations ranged between 18 and 28 ng/mL and were not detectable in one of the studies (assay sensitivity 7 ng/mL). The clinical relevance of this finding is unknown.
Data from animal studies in which neonatal rats received 3TC-HBV at much higher concentrations via maternal milk suggest that the concentrations of lamivudine in human breast milk are unlikely to produce toxicity in breast fed infants.
3TC-HBV should only be used in a nursing mother if the expected benefit justifies the potential risk to the infant. A decision must be made whether to discontinue breast-feeding or to discontinue/abstain from 3TC-HBV therapy, taking into account the benefit of breast-feeding for the child and the benefit of therapy for the woman.
