Conclusion. Patients 60 years of age or older living with virologically suppressed HIV may benefit from improved bone mineral density by switching from a TDF-containing ART regimen to a TAF-containing regimen after 48 weeks, which, in turn, may help to reduce the risk for osteoporosis. Patients who were switched to a TAF-containing regimen also had favorable improvements in UACR and UPCR, which could indicate better renal function.
Commentary
The Centers for Disease Control and Prevention estimated that in 2018 nearly half of those living with HIV in the United States were older than 50 years.1 Today, the life expectancy of patients living with HIV on ART in developed countries is similar to that of patients not living with HIV. A meta-analysis published in 2017 estimated that patients diagnosed with HIV at age 20 beginning ART have a life expectancy of 63 years, and another study estimated that life expectancy in such patients is 89.1% of that of the general population in Canada.2,3 Overall, most people living with HIV infection are aging and at risk for medical conditions similar to persons without HIV disease. However, rates of osteoporosis in elderly patients with HIV are estimated to be 3 times greater than rates in persons without HIV.4 As a result, it is becoming increasingly important to find ways to decrease the risk of osteoporosis in these patients.
ART typically includes a nucleoside reverse transcriptase inhibitor (NRTI) combination and a third agent, such as an integrase strand inhibitor. Tenofovir is a commonly used backbone NRTI that comes in 2 forms, TDF (tenofovir disoproxil fumarate) and TAF (tenofovir alafenamide). Both are prodrugs that are converted to tenofovir diphosphate. TDF specifically is associated with an increased risk of bone loss and nephrotoxicity. The loss in bone mineral density is most similar to the bone loss seen with oral glucocorticoids.5 TDF has been shown to increase plasma levels of RANKL and tumor necrosis factor-α, leading to increased bone resorption.6 The long-term effects of TDF- versus TAF-containing ART on bone mineral density have, to our knowledge, not been compared previously in a randomized control study. The significance of demonstrating an increase in bone mineral density in the prevention of osteoporotic bone fracture in people living with HIV is less clear. A long-term cohort study completed in Japan looking at patients on TDF showed an increased risk of bone fractures in both older postmenopausal women and younger men.7 However, a retrospective cohort study looking at 1981 patients with HIV found no association between bone fractures and TDF.8
This randomized controlled trial used appropriate methods to measure the reported primary and secondary endpoints; however, it would be of benefit to continue following these patients to measure their true long-term risk of osteoporosis-related complications. In terms of the study’s secondary endpoints, it is notable that the patients maintained HIV viral suppression after the switch and CD4 counts remained stable (with a slight increase observed in the TAF-containing ART cohort).
In regard to the patient’s renal function, patients in the TAF group had significantly improved UACR and UPCR, which likely reflects improved glomerular filtration. Improved renal function is also increasingly important for patients with HIV, as up to 48.5% have some form of chronic kidney disease.9