Temperature-related absorption and excretion of oxolinic acid in rainbow trout ( Oncorhynchus mykiss)

The absorption and elimination of oxolinic acid in serum, bile and tissues of rainbow trout were studied at 5, 10 and 15 °C after a single oral dose of 75 mg/kg. The maximum levels of oxolinic acid were obtained in serum within 1, 4 and 6 days at 16, 10 and 5 °C, respectively. The highest drug concentrations were measured in bile followed by liver, kidney, muscle tissue and serum. The higher levels of oxolinic acid in tissues compared to serum indicate a good distribution of the drug. The elimination half-life in serum was 24 h at 16 °C, 4.0 days at 10 °C and 6.1 days at 5 °C. With the detection limit of 0.01 μg/g for the oxolinic acid HPLC assay, the predicted withdrawal time with 95% confidence for muscle tissue was 28 days at 16 °C, 60 days at 10 °C and 140 days at 5 °C. Results obtained under laboratory conditions were in accordance with results from field trials.