Thigh Injections of Cabotegravir + Rilpivirine in Virally Suppressed Adults with HIV-1: A Substudy of the Phase 3b ATLAS-2M Study

Background Cabotegravir + rilpivirine (CAB + RPV) administered via intramuscular gluteal injections is the first complete long-acting regimen for maintaining human immunodeficiency virus type 1 (HIV-1) virologic suppression. We present substudy results on short-term repeat intramuscular CAB + RPV long-acting thigh injections in participants with ≥3 years of experience with gluteal administration during the ATLAS-2M study. Methods Substudy phases included screening, thigh injection (day 1-week 16), and return to gluteal injection (week 16-week 24). The injection schedule was unchanged from the main study. Outcomes included pharmacokinetics, safety, tolerability, efficacy, and patient-reported outcomes. Pharmacokinetic parameters were determined using noncompartmental analysis and mixed-effects modeling. Population pharmacokinetic simulations were performed. Results There were 118 participants. In the arm that received injections every 2 months (Q2M), first CAB thigh injection including area under the concentration-time curve and maximum observed concentration (Cmax) and first RPV thigh injection Cmax and all last RPV thigh injection parameters were statistically higher vs gluteal injections (paired comparison). No significant differences occurred with once-monthly (QM) dosing. No participants had HIV-1 RNA ≥50 copies/mL after thigh injections. Overall, 4%-7% of injection site reactions (ISRs) were grade 3. Five participants withdrew due to an ISR or injection intolerability. Overall, 30% preferred thigh vs gluteal injections. Simulations demonstrated the potential for chronic/continuous QM or ≤2 consecutive Q2M thigh injections. Conclusions These data demonstrate the potential use of chronic/continuous QM and rotational/short-term QM or Q2M (≤4 months of continuous dosing), CAB + RPV long-acting intramuscular thigh administration for HIV-1 treatment.