Determination of alclofenac in equine plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method to measure plasma and urinary alclofenac levels in equine biofluids is described. Isolation of the drug from plasma is achieved using liquid-liquid extraction with diethyl ether. Reversed-phase C18 solid phase extraction is used for the extraction of free and conjugated alclofenac from urine. The reproducibility and accuracy of the method were well within acceptable limits over the concentration ranges 0-10 and 0-20 micrograms/ml, respectively, for plasma and urine. Starting with 2 ml of plasma, a concentration of 0.1 microgram/ml could easily be measured; the limit of quantification in urine (0.5 ml) was 1 microgram/ml. Hydrolysis of urine with strong alkali resulted in the decomposition of alclofenac. A pharmacokinetic profile of alclofenac in the horse is shown.