Tenofovir and tenofovir-diphosphate concentrations during pregnancy among HIV-uninfected women using oral preexposure prophylaxis

Objectives: Pregnancy is a time of increased HIV acquisition risk and pregnancy reduces concentrations of antiretrovirals used for treatment. We assessed whether pregnancy lowers concentrations of tenofovir (TFV) and tenofovir-diphosphate (TFV-DP) among HIV-uninfected women using oral preexposure prophylaxis (PrEP). Methods: We analyzed data from an open-label PrEP study, comparing concentrations of TFV in plasma and TFV-DP in dried blood spots (DBS) among 37 pregnant women and 97 nonpregnant women. Analyses controlled for adherence from daily electronic monitoring. Results: The average plasma concentration of TFV among pregnant women was 34.7 ng/ml with 22.2 average recorded doses over the prior month versus 86.5 ng/ml with 23.1 doses among nonpregnant women. After controlling for adherence, TFV concentrations were 58% lower among pregnant women, a statistically significant difference of 50.4 ng/ml (95% CI 68.3 to 32.5). The average TFV-DP concentration was 450.3 fmol/punch among pregnant women and 636.7 fmol/punch among nonpregnant women. This difference was not statistically significant after adjusting for adherence; however, among those with quantifiable TFV-DP, concentrations were 27% lower during pregnancy [202 fmol/punch (95% CI 384 to 19)]. Among participants with samples before and during pregnancy, there were significant decreases during pregnancy, controlling for adherence: 28.1 ng/ml TFV (95% CI 52.3 to 4.0) and 289.2 fmol/punch TFV-DP (95% CI 439.0 to 139.3). Conclusion: Consistent with studies among HIV-infected women on ART, we found TFV and TFV-DP concentrations were lower during pregnancy. There is no established TFV concentration threshold to achieve HIV prevention. Additional pharmacokinetic studies and studies of PrEP efficacy in pregnancy are needed.