Loss of bone mineral density with PrEP
Dr. Wilson said an issue that bears watching, assuming a large increase in the use of emtricitabine/tenofovir for HIV PrEP in adolescents is in store in the near future, is drug-related loss in bone mineral density.
He presented data on changes in bone mineral density (BMD) as measured by dual-energy x-ray absorptiometry with results assessed at a core laboratory every 6 months in a companion study to the one presented by Dr. Hosek, this one involving 72 high-HIV-risk patients aged 18-22 years on 48 weeks of open-label emtricitabine/tenofovir followed by 48 weeks off PrEP.
Consistent with what’s been seen in studies of adults on emtricitabine/tenofovir, statistically significant decreases in mean Z-scores adjusted for age, sex, and race were seen at the hip and lumbar spine in this younger population between baseline and week 48 of PrEP. The reductions in BMD were in the range of 0.1-0.2 standard deviation. That’s noteworthy because up until age 20, people are supposed to be accruing bone mineralization, he observed.
During the subsequent 48 weeks off-PrEP patients showed evidence of partial but not full remineralization.
“There’s nothing here to indicate we should stop using PrEP in this age group, but given that we’d like to see high-risk young patients remain on therapy for longer than in this 48-week study, I think it would be smart to get longer-term exposure data to ensure that we still believe it’s safe,” the pediatrician commented.
Reassuringly, there is no evidence of an increase in fractures or complaints of bone pain in any studies of HIV-positive patients on tenofovir, he observed.
Because it’s unrealistic to expect to be able to routinely do serial DEXA scans in young patients on emtricitabine/tenofovir once PrEP is ramped up to the scale HIV specialists are hoping for, Dr. Wilson said he and his coinvestigators are now looking at potential biomarkers of clinically significant bone loss in young patients on chemoprophylaxis.
Dr. Wilson drew attention to the disturbingly high HIV seroconversion rate of 7.2% per year following discontinuation of PrEP after 48 weeks.
“Remember, this is a population that had already gone through extensive counseling, behavioral interventions, and personalized prevention and adherence support during the 48 weeks they were on the study drug, so they had been informed as to what the risks were. Yet we still end up with one of the highest seroconversion rates observed in any PrEP study. That tells us we still have a lot of work to do in these particular young populations,” according to Dr. Wilson.
These clinical trials of PrEP in 15- to 17- and 18- to 22-year-olds were carried out by the Adolescent Medicine Trials Network for HIV/AIDS Interventions with funding from the National Institutes of Health. Dr. Husek and Dr. Wilson reported having no financial conflicts.