Oxytetracycline and oxolinic acid residues in kuruma prawn (Penaeus japonicus) and the effect of cooking procedures on the residues

Tissue distribution and residue depletion of oxytetracycline (OTC) and oxolinic acid (OA) were studied in the kuruma prawn (Penaeus japonicus). The prawn were kept in tanks with recirculated artificial seawater at a salinity of 22similar to23parts per thousand. The water temperature was maintained at 25degreesC. The average body weight was 22.9+/-4.9 g for OTC and 22.5+/-3.6 g for OA. The drug was mixed with the diet and orally administered through a catheter to the prawn. The doses of OTC and OA, respectively, were 50 mg/kg body weight. At each sample time, four prawns were sacrificed and tissues were sampled. OTC and OA levels were determined by high-performance liquid chromatography. At the highest levels, the concentrations of OTC were in the order: shell (13.57 mug/g) > hemolymph (12.20 mug/mL) > muscle (8.30 mug/g). For OA, the order was: shell (20.74 mug/g) > hemolymph (7.06 mug/mL) > muscle (2.05 mug/g). The elimination half-lives of hemolymph and muscle were 44.7 and 46.8 hours for OTC and 55.0 and 107.9 hours for OA, respectively. Residual OTC could not be detected in hemolymph and muscle at 20 days after dosing. Residual OA disappeared from hemolymph and muscle at 25 days after dosing. A 25-day period for OTC and 30-day period for OA could be regarded as the proper withdrawal time established for kuruma prawn by the Pharmaceutical Law in Japan. However, the elimination half-lives of shell for OTC and OA could not be calculated because both drug residues persisted in shell tissues, and the elimination phase was not completed during the experimental period. Residual OTC (14.10+/-2.26 mug/g, n = 6) and OA (0.32+/-0.06 mug/g, n = 7) were detected in exuviae at 3 days and 4 days after dosing, respectively. Residual OTC was reduced to 50similar to70% in muscle by the usual methods of cooking (boiling, baking at 200degreesC and frying at 180degreesC), whereas reduction levels in shell were only 20similar to30%. Residual OA was reduced to 20similar to30% in muscle and shell by the cooking. These results confirm that the cooking procedures could only reduce but not completely eliminate these drug residues in prawn.