Evaluating the Safety, Tolerability, and Disposition of Trazpiroben, a D₂/D₃ Receptor Antagonist: Phase I Single‐ and Multiple‐Ascending Dose Studies in Healthy Japanese Participants

Trazpiroben (TAK-906) is a peripherally selective dopamine D₂ /D₃ receptor antagonist being developed to treat chronic gastroparesis. This phase I, randomized, double-blind, placebo-controlled, single- and multiple-ascending dose, parallel-group study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of trazpiroben in healthy Japanese men. Findings were compared with those from a prior US trial in healthy individuals. Overall, 24 participants were enrolled into 3 cohorts (each n = 8). Per cohort, 6 participants received trazpiroben (cohort 1, 50 mg; 2, 100 mg; 3, 10 mg) once on day 1 and twice daily on days 3 through 7, and two received placebo. Trazpiroben was well tolerated, with no clinically meaningful adverse events observed. Following single- and multiple-dose administration, trazpiroben was rapidly absorbed and eliminated (mean elimination half-life, 1.89-6.45 hours; median time to maximum serum concentration [steady state], 1.00-1.25 hours). Serum prolactin increased with trazpiroben treatment (mean maximum serum concentration 93.32 ng/mL [10 mg] vs. 10.83 ng/mL [placebo]), illustrating receptor target engagement. Results reflected those from healthy US participants, indicating a lack of differences between these ethnic populations in trazpiroben disposition and safety profile. Trazpiroben may represent a promising therapy for chronic gastroparesis across different populations, with further evaluation ongoing in a phase IIb study (NCT03544229).