1288. Bone Safety Outcomes with F/TAF vs. F/TDF for PrEP in the DISCOVER Trial

BACKGROUND: In the DISCOVER PrEP trial, emtricitabine/tenofovir alafenamide (F/TAF) was noninferior to emtricitabine/tenofovir disoproxil fumarate (F/TDF) for HIV prevention. Here we report the bone safety outcomes of F/TAF and F/TDF. METHODS: Men who have sex with men (MSM) and transgender women (TGW) at risk of HIV were randomized 1:1 to receive blinded F/TDF or F/TAF, taken once daily. Those on PrEP with F/TDF were eligible to enroll. Bone densitometry (DXA) of the hip and spine were performed in a subset of participants (BMD subset). Fracture events were compared in all study participants. Week 48 data are presented. RESULTS: 5387 participants were enrolled in the main study, with 383 included in the BMD subset. In the BMD subset, the median age was 37 (IQR 29, 46); 0.8% were TGW, 9.4% were black, and 20.6% were Hispanic or Latinx. Fifty-three BMD subset participants were on baseline F/TDF PrEP at enrollment, 26 of whom were randomized to F/TAF. F/TAF was associated with more favorable changes in hip and spine BMD compared with F/TDF (Table 1); these differences were similar when participants on baseline PrEP were excluded. Participants age <35 on F/TAF gained BMD, whereas those on F/TDF lost BMD (Table 1). BMD decreases of ≥3% were less frequent in the F/TAF group than the F/TDF group at the hip (3.8% vs. 18.4%, P < 0.001) and spine (10.1% vs. 26.9%, P < 0.001). Osteopenia was more frequently diagnosed in the spine in participants on F/TDF compared with F/TAF (Figure 1, P = 0.007); but not in the hip. Fracture event frequency was the same (53 [2.0%] per group, P = 1.00). One pathological fracture was reported in the F/TAF group compared with two in the F/TDF group (P = 0.57). In participants on baseline F/TDF PrEP, those randomized to F/TAF had significantly improved hip BMD compared with baseline (median percent change 1.13 [IQR −0.86, 3.47], P = 0.027), while spine BMD was unchanged. CONCLUSION: Through 48 weeks, DXA subset participants taking F/TAF for PrEP had significantly less change in BMD than those taking F/TDF, and were less likely to develop spine osteopenia. The incidence of fracture was similar, and pathological fractures were rare. F/TAF for PrEP is effective and has a superior bone safety profile compared with F/TDF. [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.