Serum and urine as predictors of sulfamethazine levels in swine muscle, liver and kidney

Three field studies were done to determine the relationship between sulfamethazine levels in swine serum and urine, and those in swine muscle, liver and kidney. The 119 animals used in these studies were crossbreed Landrace, Yorkshire, White and Chester White pigs. The medication, Aureo-SP-250, was added to the ration to achieve a sulfamethazine feed concentration of 110 ppm. The swine were divided into groups, with the treatment groups receiving feed containing no medication for 0 to 8 d after being on the medicated feed for 19 to 20 d. Control groups also received nonmedicated feed. Results from the three studies were pooled and predictive relationships were developed in the form: Tissue Concentration = Ratio × Fluid Concentration. For serum, the mean tissue-fluid ratios in muscle, liver and kindey were 0.24, 0.90 and 0.53, respectively; the ratios for urine were 0.08, 0.27 and 0.16, respectively. Previous reports indicate serum can be used to predict sulfamethazine levels in muscle, liver and kidney. No reports concerning tissue-urine data have been published; however, the three studies reported here indicate that the tissue-urine relationship, although more variable, can also be used as a predictor. The observed variability caused by biological, analytical or other factors must be considered when using either urine or serum to predict muscle, liver or kidney sulfamethazine levels. These studies show promise for quality control or regulatory use by the slaughter plant, farm or laboratory as a predictor of sulfamethazine levels in tissues.