Modeling and allometric scaling of s(+)-ketoprofen pharmacokinetics and pharmacodynamics: A retrospective analysis

Interspecies scaling of pharmacokinetic (PK) parameters is commonplace in drug development. However, information about proportionality of pharmacodynamic (PD) parameters in different species is scarce. We investigated the feasibility of allometric scaling of PK and PD parameters of s(+)-ketoprofen (sKTP) using the literature data from several animal species. Two different indirect response models were proposed to characterize sKTP inhibitory effects on synthesis of thromboxane B₂ (TXB₂) and prostaglandin E₂ (PGE₂). Using the traditional allometric approach, the obtained PK and PD parameters were plotted against body weights (BW) on a log-log scale. For all species, values of systemic clearance (Cl), distribution clearance (Cl _D), central volume of distribution (V_c), and volume of distribution at steady-state (V_ss) were highly correlated (r ² = 0.89-0.99) with BW. The PD parameters for inhibition of TXB ₂ synthesis were poorly correlated with BW (r² = 0.25-0.54) while most of the parameters for inhibition of PGE₂ synthesis lacked any correlation (r² ≈ 0.05). In conclusion, indirect response models adequately described the time course of sKTP inhibitory effects on synthesis of TXB₂ and PGE₂. Allometrical scaling showed PK parameters to change proportionally to BW, whereas PD parameters had limited ranges and were essentially weight independent.