Multiparametric magnetic resonance imaging to characterize cabotegravir long-acting formulation depot kinetics in healthy adult volunteers

Aim Cabotegravir long-acting (LA) intramuscular (IM) injection is being investigated for HIV preexposure prophylaxis due to its potent antiretroviral activity and infrequent dosing requirement. A subset of healthy adult volunteers participating in a phase I study assessing cabotegravir tissue pharmacokinetics underwent serial magnetic resonance imaging (MRI) to assess drug depot localization and kinetics following a single cabotegravir LA IM targeted injection. Methods Eight participants (four men, four women) were administered cabotegravir LA 600 mg under ultrasonographic-guided injection targeting the gluteal muscles. MRI was performed to determine injection-site location in gluteal muscle (IM), subcutaneous (SC) adipose tissue, and combined IM/SC compartments and to quantify drug depot characteristics, including volume and surface area, on Days 1 (≤2 hours postinjection), 3, and 8. Linear regression analysis examined correlations between MRI-derived parameters and plasma cabotegravir exposure metrics, including maximum observed concentration (Cmax ) and partial area under the concentration-time curve (AUC) through Weeks 4 and 8. Results Cabotegravir LA depot locations varied by participant and were identified in the IM compartment (n=2), combined IM/SC compartments (n=4), SC compartment (n=1), and retroperitoneal cavity (n=1). Although several MRI parameter and exposure metric correlations were determined, total depot surface area on Day 1 strongly correlated with plasma cabotegravir concentration at Days 3 and 8, Cmax , and partial AUC through Weeks 4 and 8. Conclusion MRI clearly delineated cabotegravir LA injection-site location and depot kinetics in healthy adults. Although injection-site variability was observed, drug depot surface area correlated with both plasma Cmax and partial AUC independently of anatomical distribution.