Simultaneous determination of sulphadiazine and trimethoprim in plasma and tissues of cultured fish for residual and pharmacokinetic studies.

Clean-up and high-performance liquid chromatographic methods for the simultaneous determination of sulphadiazine and trimethoprim in fish plasma and tissues have been developed. The average recovery of sulphadiazine varied from 74% in liver to 92% in plasma, whereas that of trimethoprim varied from 60% in liver to 97% in plasma. The sample pretreatment procedures were simple, selective and robust, having a limit of quantification of 250 ng/ml for trimethoprim and 50 ng/ml for sulphadiazine in plasma, 15 ng/g for sulphadiazine and 80 ng/g for trimethoprim in muscle, and 30 ng/g for sulphadiazine and 160 ng/g for trimethoprim in liver. The assay was tested on plasma from Atlantic salmon treated with Tribrissen.