Longitudinal changes in tenofovir and tenofovir-diphosphate concentrations among pregnant women using oral PrEP for HIV prevention: Findings from Durban, South Africa.

Background: Pregnant women are vulnerable to HIV acquisition. Oral HIV pre-exposure prophylaxis (PrEP) is safe and effective for use during pregnancy. We describe PrEP adherence among pregnant women using multiple measures.

Methods: We conducted a secondary data analysis among women enrolled in a study evaluating an adherence intervention for PrEP among those planning for and with pregnancy in South Africa. Our analysis included women who used PrEP and became pregnant. Longitudinal PrEP use was assessed using concentrations of tenofovir (TFV) in plasma, tenofovir diphosphate (TFV-DP) in dried blood spots, and electronic pillcap data from quarterly visits. Plasma TFV ≤ 10ng/mL and TFV-DP ≤ 16.6fmol/punch were below quantifiable limits. Data were analysed over pre-pregnancy (quarter prior to pregnancy) and pregnancy trimesters.

Results: Among 35 women, 69% were 18-24 years old, 40% were nulliparous, and 94% did not know their partner's HIV-serostatus. Median pillcap adherence was 55%-80% and was highest during pre-pregnancy (72%, IQR:54%-86%) and third trimester (80%, IQR:30%-94%). The proportion of women with quantifiable TFV was 47% (n=8/17) pre-pregnancy and 33% (n=9/27), 19% (n=4/21), and 14% (n=2/14) for trimesters 1-3, respectively. TFV-DP was detected in 75% of samples (n=12/16) pre-pregnancy, and 50% (n=13/26), 29% (n=6/21), and 27% (n=4/15) for trimesters 1-3. No women acquired HIV during pregnancy.

Conclusions: PrEP use declined during pregnancy by all measures. Discrepancies between pillcap measurements and drug concentrations could be due to physiologic changes during pregnancy or under- or over-use of the pillcaps. Determining what drug metabolite concentrations are needed to confer protection during pregnancy is important to optimizing counselling and prevention support.