At a time when their bone mineral density (BMD) would normally increase, young men taking Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP) against HIV in a recent study saw their levels decline, raising concerns that they may experience fragility later in life. Researchers conducted an analysis of bone density changes among 18-to-22-year-old gay male participants in the ATN open-label demonstration project of PrEP. Findings were presented at the 15th European AIDS Conference and the 17th International Workshop on Comorbidities and Adverse Reactions in HIV.

BMD typically peaks at about age 20 and gradually drops thereafter. This peak level helps predict the risk of bone fractures in the future.

The demonstration project included 200 at-risk men in 12 U.S. cities. They had a median age of 20. About half were black and a quarter Latino. They were offered daily Truvada for 48 weeks.

For this bone substudy, participants were given scans of the hip, spine and whole body at the beginning, middle and end of the 48-week period. Four of the participants contracted HIV during the trial and were excluded from this analysis.

On the whole, the participants had lower-than-normal BMD at the outset of the study, a phenomenon seen in other studies of high-risk HIV-negative men. A total of 8.1 percent of the participants started the study with spine BMD below the threshold for low bone mass, 6.1 percent had low hip BMD and 3.7 percent had low body BMD.

Participants whose tests showed they were taking Truvada consistently enough for high protection against HIV (on the whole, adherence was very poor) had 0.5 percent loss of spine BMD at the study midpoint and a loss of 1.5 percent at the end of the study. Meanwhile, those who were not apparently taking any Truvada experienced an increase in their BMD by about the same factors. Those with highly protected Truvada levels experienced smaller drops in their hip BMD, while those with undetectable levels of the drug did not see a change in their hip BMD. There was no apparent difference in bone loss between those apparently taking four pills of Truvada a week compared with those taking seven pills.

Five men experienced bone fractures during the study, all of them as a result of trauma. None of them had low bone mass.

The researchers concluded, “Although the BMD losses were generally modest, their occurrence before attainment of peak bone mass in young men who already have low bone mass may increase their risk of fragility in adulthood.”

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