A Population Pharmacokinetic and Pharmacodynamic Analysis of RP5063 Phase 2 Study Data in Patients with Schizophrenia or Schizoaffective Disorder

Marc Cantillon, Robert Ings, Arul Prakash, Laxminarayan Bhat

RP5063 is a novel multimodal dopamine (D)-serotonin (5-HT) stabilizer possessing partial agonist activity for D2/3/4and 5-HT1A/2A, antagonist activity for 5-HT2B/2C/7,and moderate affinity for the serotonin transporter. Phase 2 trial data analysis of RP5063 involving patients with schizophrenia and schizoaffective disorder defined: (1) the pharmacokinetic profile; and (2) the pharmacokinetic/pharmacodynamic relationships. Pharmacokinetic sample data (175 patients on RP5063; 28 doses/patient) were analyzed, utilized one- and two-compartment models, and evaluated the impact of covariates. Pharmacodynamic analysis involved development of an Emaxmodel. The pharmacokinetic analysis identified a one-compartment model incorporating body mass index influence on volume as the optimum construct, with fixed-effect parameters: (1) oral clearance (Cl/F), 5.11 ± 0.11 L/h; (2) volume of distribution (Vc/F), 328.00 ± 31.40 L; (3) absorption constant (ka) 0.42 ± 0.17 h-1; (4) lag time (t lag) of 0.41 ± 0.02 h; and (5) a calculated half-life of 44.5 h. Pharmacokinetics were linear related to dose. An Emaxmodel for total Positive and Negative Syndrome Scale (PANSS) scores as the response factor against cumulative area under the curve (AUC) provided fixed-effect estimates: (1) Eo = 87.3 ± 0.71 (PANSS Units; pu); (2) Emax = - 31.60 ± 4.05 (pu); and (3) AUC50 = 89.60 ± 30.10 (µg·h/mL). The predicted PANSS improvement reflected a clinical dose range of 5-30 mg. Pharmacokinetics of RP5063 behaved predictably and consistently. Pharmacodynamics were characterized using an Emaxmodel, reflecting total PANSS score as a function of cumulative AUC, that showed high predictability and low variability when correlated with actual observations.