Evaluation of selected antibiotics for potential use in penaeid shrimp aquaculture.

Abstract

Select antibacterials were evaluated for their potential as shrimp aquaculture drugs. Difloxacin and sarafloxacin were evaluated for palatability, toxocity, and residues with respect to shrimp, after 15 days of feeding medicated diets. The pharmacokinetics and bioavailabilities of sulphadimethoxine (SDM) and ormetoprim (OMP) were also established for shrimp. Reductions (p < 0.05) in difloxacin feed palatability were noted as a function of dose. Total survival and mean survival time (p < 0.05) decreased as a function of dose. Signs of animal stress, i.e., lethargic behavior, was also noted in the highest dose group. Shrimp tissue levels of difloxacin were inconclusive and not readily determined with the current analytical methods for the drug in shrimp. However, indications were that elimination may be rapid, i.e., tissue t1/2 of 11.4 h with peak tissue levels following a standard dose response. Feed palatability was reduced (p < 0.05) as a function of sarafloxacin dose. Lower weight gains in the higher dose groups were also noted. Neither the total survival nor the mean survival time (p < 0.05) were affected by sarafloxacin dose. Feed Conversion Ratio's increased with dose, indicating possible subchronic toxicity. Sarafloxacin elimination was rapid, with a tissue t1/2 of 13.4 h and tissue levels decreased to below detectable limits by day 14 of withdrawal in all treatments. Peak tissue levels followed a standard dose response. The hemolymph concentrations versus time data for both SDM and OMP were fitted well by two compartment models. The SDM:OMP parameter estimates of CLs, Vss, and terminal phase t1/2 were 194:2045 ml/kg*h, 1735:25,442 ml/kg, and 6.9:11.5 h, respectively. Plasma protein binding of SDM and OMP was 5.2% and 12.1%, respectively. The bioavailabilities of SDM:OMP were 30:38%. Peak hemolymph concentration (Cmax) and time (Tmax) of SDM post of single oral dose (210 mg/kg) was 14 ug/ml at 4 h, while OMP (42 mg/kg) Cmax and Tmax was 0.45 ug/ml at 0.67 h. The amount of the available oral dose 2 h post administration of SDM:OMP in the hemolymph, muscle, and hepatopancreas were 6.0:0.5%, 9.3:2.8%, and 2.9:20.2%, respectively. Hemolymph and muscle tissue levels were below detectable limits post 48h for SDM and 24 h for OMP.