Deciphering the Combined Effects of Hydroxysafflor Yellow A and Calycosin Through Coupled PK–PD Modeling

To quantitatively characterize the pharmacokinetic and pharmacodynamic interactions between Hydroxysafflor Yellow A (HSYA) and Calycosin (CA) in cerebral ischemia–reperfusion injury (CIRI), a factorial experimental design was combined with a hierarchical coupled PK-PD modeling framework. The coupled PK model adequately described the concentration-time profiles of HSYA and CA under co-administration, with R2 values of 0.83 and 0.86, respectively, while the PK-PD model showed good fitting performance for Caspase-3 and HIF-1α, with all R2 values exceeding 0.97. Structural identifiability analysis showed that the newly introduced PK and PD coupling parameters were globally identifiable, and their Bootstrap 95% confidence intervals excluded zero. After Holm-Bonferroni correction, AUC0-t, AUC0-∞ and CL differed significantly between single and combined administration, whereas MRT did not. The model-derived relative contribution weights of HSYA and CA were quantified for both Caspase-3 and HIF-1α, with uncertainty assessed using Bootstrap 95% confidence intervals. Overall, the proposed coupled PK-PD framework provides a quantitative approach for characterizing component interactions and relative pharmacodynamic contributions in multi-component systems.