Background: Pre-exposure prophylaxis (PrEP) with FTC/TDF is a biologically potent strategy for interrupting HIV transmission. PrEP requires a chain of engagement termed the “prevention cascade” — seeking services, initiating FTC/TDF, HIV testing, medication refills and adequate adherence. We characterize this spectrum and identify potential predictors of engagement in the iPrEx OLE study.
Methods: iPrEx OLE examined open-label PrEP uptake and adherence by enrolling men who have sex with men and transgender women at 11 sites in 6 countries and offering up to 18 months of open label FTC/TDF to HIV- former participants in 3 PrEP trials. They were followed quarterly with HIV testing and medical assessments regardless of whether they elected to receive PrEP. Exposure to FTC/TDF used a case/cohort design to test for TFV-DP in dried blood spots (DBS) collected for all on-PrEP seroconverters (n=28) and a randomly selected sample (n=325, 27%) of the cohort. iPrEx OLE showed TFV-DP levels ^ 700 fmol/punch (consistent with ^ 4 pills per week) as highly protective against HIV infection. Predictors of a DBS levels of ^ 700 fmol/punch were assessed in a probability weighted multivariable logistic regression model.
Results: Of 1603 HIV- participants, 1125 (76%) initiated PrEP. At the 12 month visit after starting PrEP, 1005 of initiators (84%) attended, 813 had been dispensed PrEP at the last visit, and an estimated 354 had TFV-DP levels ^ 700 fmol/punch, yielding highly protective concentrations at 12 months in 22% of those offered PrEP. These percentages were 34% at 3 months and 26% at 6 months. TFV-DP levels ^ 700 fmol/punch at 12 months varied by site (p < 0.001) ranging from 11% to 63% of those offered PrEP. Percentages were higher among those reporting non-condom insertive anal intercourse (ncIAI) (p=0.02), a diagnosed sexual transmitted infection (p=0.046), a HIV+ partner (p=0.02), and secondary (p=0.03) or higher (P< 0.001) education. No significant differences were observed by transgender identity, age, non-condom receptive anal intercourse or drug useConclusions: There are challenges across the prevention cascade in uptake of PrEP, as well as engagement with and adherence to PrEP. Less than half of participants who attended study visits and were dispensed medication had TFV-DP levels consistent with ^ 4 pills per week. Prevention engagement was higher among participants with secondary education, a HIV+ positive partner, a sexually transmitted infection, and ncIAI.