We all make countless assumptions every day. We assume that in the morning the kettle and toaster will do their jobs, that the car will start or that our train will arrive at the station. We make assumptions about our partners, our family members, our colleagues and our friends, and about strangers. Our assumptions about our environment and the people around us are often based on nothing more than irrational notions, concepts, beliefs and attitudes which are very rarely based on fact.
Taking tenofovir/emtricitabine (Truvada) as pre-exposure prophylaxis (PrEP) has little effect on kidney function, according to a study recently published in AIDS. The study, known as IPrEx (Iniciativa Profilaxis Pre-Exposicion), showed a very mild decrease in creatinine clearance (CrCl) — a measure of kidney function — among participants taking Truvada, but the change was reversible, as CrCl returned to baseline levels after the drug was discontinued at the end of the study.
IPrEx followed 2499 HIV-negative men who have sex with men (MSM) and transgender women, across sites in Latin America, the United States and Thailand. The study previously demonstrated that once-daily Truvada was 44% effective in decreasing HIV infection rates, compared to taking a placebo, despite low adherence in a subset of participants.
Study participants were randomized to take either tenofovir/emtricitabine or a placebo for an average of 81 weeks. A statistically significant decrease in CrCl (which reflects an increase in serum creatinine) was observed starting at week four (mean change: -2.4 vs. -1.1 ml/min; P = .02) and lasted through the end of treatment (mean change: +0.3 vs. +1.8 ml/min; P = .02), but CrCl returned to baseline after stopping the study drug (mean change: 0.1 vs. 0.0 ml/min; P =.83). These mean changes reflected a small difference in a large portion of the treatment group.
Week four of the study also saw a trend toward a greater decrease in serum phosphorus levels among study subjects (mean change from baseline tenofovir/emtricitabine: -0.0t mg/dl vs. placebo: mean -0.01 mg/dl; P = .06), although phosphorus levels did not significantly change over time.
Previous studies, such as the Swiss HIV Cohort Study, had associated tenofovir (Viread) with another kidney problem, proximal renal tubulopathy (PRT). However, a substudy of 1,137 IPrEx participants found no indication of PRT in 94% of that group. Those who did develop PRT had been randomized to the placebo arm of the study, so their renal troubles were not related to being on PrEP.
Similar studies in HIV-positive people had shown a somewhat higher degree of renal function impairment, which did not always resolve itself after tenofovir/emtricitabine was stopped. By contrast, the almost 2,500 participants in this study had no pre-existing risk factors for renal disease, such as infection with HIV or hepatitis B. However, the low adherence to PrEP might have mitigated some of the renal effects of the medication.
While tenofovir/emtricitabine as PrEP does not appear to cause kidney damage, the study authors recommend monitoring the renal safety of PrEP as it becomes more widely available to people who may be predisposed to kidney problems. They also caution that a second test for kidney function should be performed before stopping tenofovir/emtricitabine, because most creatinine elevations are self-limiting.