Population Pharmacokinetics for Pediatric Extrapolation of GenSci006: A 3.75-mg Triptorelin Acetate Microsphere...

Triptorelin acetate microspheres are long-acting gonadotropin-releasing hormone (GnRH) agonist used for treating central precocious puberty (CPP). GenSci006 is a newly developed 3.75-mg formulation intended as a local alternative to Diphereline^®. This study aimed to characterize the pharmacokinetics (PK) of GenSci006 using population pharmacokinetic (PopPK) modeling with pediatric extrapolation, to evaluate pharmacodynamic (PD) comparability, and to support a fixed-dose regimen for CPP.

This study comprised two components: (1) PopPK modeling and model-based simulation to characterize exposure and support pediatric extrapolation; and (2) a comparative pharmacodynamic assessment based on serum luteinizing hormone (LH) responses.

The final PopPK model employed a three-compartment structure with mixed sequential absorption phases (two first-order and a zero-order absorption), capturing triptorelin's multiphasic release. Covariates, including weight, age, albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), serum creatinine, total bilirubin, and creatinine clearance, showed no significant effect on PK. Allometric scaling (exponents 0.75 for clearance [CL] and 1 for central volume distribution [V₃]) was applied to simulate pediatric exposure. Simulations indicated that at a fixed 3.75-mg dose, exposure decreased with increasing weight, with an approximately 1.7-fold difference between the 20-30 kg and 40-50 kg groups. In the comparative PD analysis, serum LH exposure profiles were comparable between GenSci006 and the reference product over the 0-672-h assessment period.

Model-based simulations predicted approximately two-fold higher exposure in lighter children (20-30 kg) compared with adults. This difference was not clinically meaningful given the plateau PD effect and wide therapeutic range of triptorelin.