San Francisco—The CDC estimates that daily use of pre-exposure prophylaxis (PrEP) reduces the risk of getting HIV from sex by more than 90% and from injection-drug use by more than 70%.

While PrEP is highly effective in those at high risk of getting HIV, some previous studies raised concerns about a high cost: decreases in bone density.

A study published in AIDS Research and Human Retroviruses suggests that those worries had the potential of decreasing PrEP users.

Researchers led by the University of California San Francisco helps puts some of those concerns to rest, however. The study team reports that among users of PrEP “to prevent against AIDS that includes tenofovir, marketed as Truvada, those with daily use —very high adherence—had only about a 1% average decrease in bone mineral density in the spine and a 0.5% decline in the hip.”

To reach those conclusions, the study team used estimated PrEP adherence data and measurements of bone density using dual-energy x-ray absorptiometry (DXA) over a median of 24 weeks.

Participants included cisgender men who have sex with men and transwomen who were part of the optional DXA substudy of a large, international, open-label PrEP demonstration project, the iPrEx-open-label extension (OLE) study. The subjects underwent DXA scans and dried blood spot (DBS) collection every 24 weeks, with average weekly dosing adherence patterns—two, four, or seven doses/week—estimated from validated tenofovir-diphosphate cut-offs.

Researchers report that DXA/DBS data were available for 254 individuals over a median of 24 weeks in iPrEx-OLE from June 2011 to December 2013. Results indicate that participants with estimated daily adherence experienced a 1.2% decrease in spine BMD and a 0.5% drop in hip BMD.

“In highly adherent PrEP users, we found a lower-than-expected drop in BMD when compared with previous studies,” the authors report. “This drop is likely not clinically significant for most PrEP users. However, for those at the highest risk of fracture who plan prolonged PrEP use, alternate PrEP strategies could be considered.”

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