Pharmacokinetics and metabolism of sulphamonomethoxine in rainbow trout (Oncorhynchus mykiss) and yellowtail (Seriola quinqueradiata) following bolus intravascular administration

Abstract The present study examined the pharmacokinetics and metabolism of sulphamonomethoxine (SMM) in rainbow trout ( Oncorhynchus mykiss ) and yellowtail ( Seriola quinqueradiata ) after intravascular administration (100 mg kg −1 body weight). Rainbow trout and yellowtail were kept in tanks with running water at 15.0 ± 0.3 °C and running sea water at 21.3 ± 0.2 °C, respectively. Serum concentrations of SMM were determined using high performance liquid chromatography with direct injection. Serum concentrations of SMM in rainbow trout and yellowtail were best described by a two-compartment model. The calculated half-lives for the distribution phase and the elimination phase were 0.43 h and 30.9 h for rainbow trout, and 0.53 h and 5.8 h for yellowtail, respectively. The apparent volume of distribution ( V d ) was larger in rainbow trout ( V d = 0.83 1 kg −1 ) than in yellowtail ( V d = 0.56 1 kg −1 ). Total body clearance was calculated as 18.5 ml kg −1 h −1 in rainbow trout and 66.7 ml kg −1 h −1 in yellowtail. The behaviour of N 4 -acetyl metabolite, N 4 -acetylsulphamonomethoxine (AcSMM), in rainbow trout and yellowtail could be explained well by a one-compartment model. The formation rate constant of the metabolite and the elimination half-lives were 0.0694 h −1 and 15.4 h for rainbow trout, and 0.1896 h −1 and 8.1 h for yellowtail, respectively. Acetylation in rainbow trout and yellowtail was calculated to be 23% and 64%, respectively. The serum protein bindings in vivo of SMM and AcSMM were determined to be 6.4 ± 2.3% and 9.5 ± 3.6% for rainbow trout, and 5.8 ± 1.7% and 6.3 ± 2.3% for yellowtail, respectively.