The enantioselective population pharmacokinetics of intravenous ketorolac in children using a stereoselective assay suitable for microanalysis

Objective: To describe the effect of age and body size on enantiomer selective pharmacokinetic (PK) of intravenous ketorolac in children using a microanalytical assay.

Methods: Blood samples were obtained at 0, 15 and 30 min and at 1, 2, 4, 6, 8 and 12 h after a weight-dependent dose of ketorolac. Enantiomer concentration was measured using a liquid chromatography tandem mass spectrometry method. Non-linear mixed-effect modelling was used to assess PK parameters.

Key findings: Data from 11 children (1.7–15.6 years, weight 10.7–67.4 kg) were best described by a two-compartment model for R(+), S(−) and racemic ketorolac. Only weight (WT) significantly improved the goodness of fit. The final population models were CL = 1.5 × (WT/46)^0.75, V₁ = 8.2 × (WT/46), Q = 3.4 × (WT/46)^0.75, V₂ = 7.9 × (WT/46), CL = 2.98 × (WT/46), V₁ = 13.2 × (WT/46), Q = 2.8 × (WT/46)^0.75, V₂ = 51.5 × (WT/46), and CL = 1.1 × (WT/46)^0.75, V₁ = 4.9 × (WT/46), Q = 1.7 × (WT/46)^0.75 and V₂ = 6.3 × (WT/46)for R(+), S(−) and racemic ketorolac.

Conclusions: Only body weight influenced the PK parameters for R(+) and S(−) ketorolac. Using allometric size scaling significantly affected the clearances (CL, Q) and volumes of distribution (V₁, V₂).