The future of preexposure prophylaxis (PrEP) is here, according to interim study results demonstrating the superiority of long-acting, injectable cabotegravir (CAB-LA) over the current workhorse, daily oral tenofovir disoproxil fumarate-emtricitabine (TDF-FTC).
In a prospective, phase 2b-3 randomized, double-blind, double-dummy, active-controlled trial among 4,566 cisgender MSM (men who have sex with men) and transgender women,The study was terminated early, owing to strong evidence of efficacy in the first preplanned interim endpoint analysis. The study findings were Aug. 11 in the New England Journal of Medicine.
“The lesson is not that TDF-FTC doesn’t work or has major problems; it is a very safe, very well-tolerated agent and astonishingly effective if taken as prescribed,” Raphael J. Landovitz, MD, lead author and codirector of the Center for HIV Identification, Prevention, and Treatment Services at the University of California, Los Angeles, said in an interview.
“The reason that we were able to show that cabotegravir was superior is because we enrolled a very young, very highly at-risk, very underresourced, underrepresented, highly sexually active group who weren’t able to take PrEP the way it was prescribed,” he said.
Study participants were assigned to receive either active CAB 600 mg intramuscularly with TDF-FTC placebo or active TDF-FTC (300 mg/200 mg) with a CAB procedure in three phases:
- An oral-tablet 5-week lead-in phase, a blinded injection phase beginning at week 5.
- An injection at week 9 and every 8 weeks thereafter through week 153.
- An open-label “tail” phase consisting of oral TDF/FTC to provide ongoing for participants discontinuing injections.
The median age of study participants was 26 years (interquartile range [IQR], 22-32 years); 12.5% (570) identified as transgender women; 49.8% (845/1,698) of U.S. participants were Black patients.
During follow-up, HIV infections were identified in 57 participants, including 52 who acquired HIV infections after enrollment (13 in the CAB group, incidence 0.41 per 100 person-years, vs. 39 in the TDF-FTC group, incidence 1.22 per 100 person-years). The hazard ratio for incident HIV infection was 0.34 (95% confidence interval, 0.18-0.62) CAB vs. TDF-FTC (P < .001). Consistent effects were observed across prespecified subgroups and populations.
Among participants in the CAB group, integrase strand-transfer inhibitor resistance mutations were detected in one of four of the baseline HIV infection cases. Among participants in the TDF-FTC group, 2 of 39 incident infections occurred despite drug concentration measurements that indicated good PrEP adherence.
Although injection site reactions were reported in 81.4% (1,724) of the CAB group, only 2.4% of patients (50) discontinued treatment. Most reactions began a median of 1 day (IQR, 0-2 days) post injection. They were of mild to moderate severity (60.8% pain, 23.7% tenderness) and lasted a median of 3 days (IQR, 2-6 days). Injection site reactions were reported in 31.3% of the participants in the TDF-FTC group who received at least one placebo injection.
Rates of severe adverse effects (grade 3 or higher) were similar between participants in the CAB and TDF-FTC groups. They consisted mostly of an increase in creatine kinase level (14.2% with CAB vs. 13.5% with TDF-FTC) and a decrease in creatine clearance (7.0% with CAB vs. 8.3% with TDF-FTC).
In a post hoc analysis, the mean annualized weight increase was 1.23 kg/y (95% CI, 1.05-1.42) in the CAB group, compared with 0.37 kg/y (95% CI, 0.18-0.55) in the TDF-FTC group. Most of these differences were observed during the first 40 weeks and were driven by weight loss among TDF-FTC participants; weight changes between groups were similar thereafter (~1 kg/y for both groups).