Development of an enantiomer selective microsampling assay for the quantification of ketorolac suitable for paediatric pharmacokinetic studies.

BACKGROUND: Ketorolac, a potent nonsteroidal anti-inflammatory drug used for pain control in children, exists as a racemate of inactive R (+) and active S (-) enantiomers. AIM: To develop a microsampling assay for the enantioselective analysis of ketorolac in children. METHODS: Ketorolac enantiomers were extracted from 50 µl of plasma by liquid­liquid extraction and separated on a ChiralPak AD-RH. Detection was by a TSQ quantum triple quadrupole mass spectrometer with an electrospray ionisation source operating in a positive ion mode. Five children (age 13.8 (1.6) years, weight 52.7 (7.2) kg), were administered intravenous ketorolac 0.5mg/kg (maximum 10mg) and blood samples were taken at 0, 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h post administration. CL, VD and t1/2 were calculated based on non-compartmental methods. RESULTS: The standard curves for R (+) and S (-) ketorolac were linear in the range 0­2000 ng/ml. The LLOQs of the method were 0.15 ng on column and 0.31 ng on column for R (+) and S (-) ketorolac, respectively. The median (range) VD and CL of R (+) and S (-) ketorolac were 0.12 l/kg (0.07­0.17), 0.017 l/h/kg (0.12­0.29) and 0.17 (0.09­0.31) l/kg, 0.049 (0.02­0.1) l/h/kg, p = 0.043), respectively. The median (range) elimination half-life (t1/2) of the R (+) and S (-) ketorolac was 5.0 h (2.5­5.8) and 3.1 h (1.8­4.4), p = 0.043), respectively. CONCLUSION: The development of a simple, rapid and reliable ketorolac assay suitable for paediatric PK studies is reported.