This drug should be used during pregnancy only if the benefit outweighs the risk to the fetus.

AU TGA pregnancy category: B3
US FDA pregnancy category: Not assigned.

Risk summary: Malformative risk with use of this drug in pregnant women is unlikely.

Comments: A pregnancy exposure registry is available.

Animal studies (high-dose) have revealed evidence of embryonic and fetal toxicity, including developmental toxicity, fetal anasarca, skeletal malformations, and increased incidence of stillbirth. Placental transfer has been observed in humans. There are no controlled data in human pregnancy; however, based on observed outcomes (more than 800 after first-trimester exposure and more than 1000 after second-/third-trimester exposure), the malformative risk is unlikely in humans.

To monitor maternal-fetal outcome of pregnant women exposed to antiretroviral therapy, an Antiretroviral Pregnancy Registry (APR) has been established. Healthcare providers are encouraged to prospectively register patients. For additional information: apregistry.com

The APR has received prospective reports of over 2000 exposures to this drug (over 900 exposed in the first trimester) resulting in live births; there was no difference between abacavir and overall birth defects compared with the background birth defect rate of 2.7% in the reference population. The prevalence of defects in the first trimester was 3% for abacavir. No increased risk of major birth defects observed for this drug compared to background rate.

AU TGA pregnancy category B3: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have shown evidence of an increased occurrence of fetal damage, the significance of which is considered uncertain in humans.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decision and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

See references

Breast milk from 15 women and blood samples from 9 of their partially or exclusively breastfed infants were collected about 1 month postpartum; the mothers were using abacavir 300 mg twice a day (with lamivudine and zidovudine). Breast milk was obtained right before a dose; whole breast milk abacavir levels averaged 0.057 mg/L (about 85% of maternal blood levels). Infant blood was obtained 11 to 18 hours after the last maternal dose and about 1 hour (range: 6 minutes to 35 hours) after the last breastfeeding; plasma drug levels were undetectable (less than 16 mcg/L) in 8 of 9 infants.

Breastfeeding is not recommended during use of this drug; if replacement feeding is not an option, a different drug may be preferred.

Excreted into human milk: Yes

Comments:
-The effects in the nursing infant are unknown.
-The US CDC, American Academy of Pediatrics, and manufacturer advise HIV-infected women not to breastfeed to avoid postnatal transmission of HIV to a child who may not yet be infected.
-Local guidelines should be consulted if replacement feeding is not an option.

See references