Pharmacokinetics and pharmacodynamics of sulfamethoxazole and trimethoprim in swimming crabs (Portunus trituberculatus) and in vitro antibacterial activity against Vibrio: PK/PD of SMZ-TMP in crabs and antibacterial activity against Vibrio.

Serious bacterial pathogens have recently become a major cause of massive mortality in swimming crabs (Portunus trituberculatus). In this study, the antibacterial activity against Vibrio and the pharmacokinetics (PK) of sulfamethoxazole (SMZ)-trimethoprim (TMP) in crabs were estimated to explore the pharmacokinetics/pharmacodynamics (PK/PD) properties of the SMZ-TMP combination. The in vitro bacteriostatic activity and the anti-Vibrio infection activity of the SMZ-TMP combination at various ratios in crabs were studied. A degree of synergism was observed in the SMZ-TMP combination at ratios ranging from 50:1 to 1:5. The results showed that the MIC50 and MIC90 values for different SMZ-TMP combinations were in the ranges of 0.62-5 and 0.62-10μg/mL, respectively. The distribution of the MIC values of the SMZ-TMP combination at ratios of 1:1 and 5:1 were 0.31-5 and 0.31-10μg/mL, respectively. Crabs were then fed the SMZ-TMP combination (at ratios of 5:1 and 1:1) six successive times and then challenged with Vibrio parahaemolyticus at 1×10(5), 1×10(6), and 5×10(6) colony forming units (cfu) per crab. The results showed that the number of surviving crabs administered SMZ-TMP at a ratio of 1:1 was greater than that of the crabs given SMZ-TMP at a ratio of 5:1. In addition, the tissue distribution and absorption of SMZ-TMP (ratios of 5:1 and 1:1) in crabs were studied through high-performance liquid chromatography (HPLC). In the crabs fed SMZ-TMP at a ratio of 5:1, the CmaxSMZ/TMP values in the hemolymph, hepatopancreas, muscle and gill were 104:1. 0.57:1, 19:1 and 6:1, respectively. In contrast, the corresponding CmaxSMZ/TMP values in these tissues in the crabs fed SMZ-TMP at a ratio of 1:1 were 34:1, 0.14:1, 4:1 and 3:1, respectively. The results showed that TMP was better absorbed and eliminated in the crabs fed SMZ-TMP at a ratio of 1:1 than in the crabs fed this combination at a ratio of 5:1. In addition, TMP was absorbed and eliminated more rapidly in the hepatopancreas than in the gill, muscle and hemolymph. The distribution volume of TMP in the hepatopancreas exceeded that of SMZ observed in the experiments. The results indicated that the PK/PD effect of the SMZ-TMP at a ratio of 1:1 was greater than that of the combination at a ratio of 5:1. Our study suggests that a SMZ-TMP ratio of 1:1 may be used to control bacterial disease in aquatic animals.