Cimetidine enhances the plasma praziquantel concentration and treatment efficacy against Microcotyle sebastis in cultured rockfish Sebastes schlegeli.

The effect of cimetidine on the praziquantel concentration in the blood of the rockfish Sebastes schlegeli and the consequent effect on the treatment efficacy against Microcotyle sebastis were investigated. Fish were divided into 7 groups and orally administered praziquantel alone (200 and 100 mg kg(-1) body weight [BW]) or in combination with cimetidine (in doses of 200, 100 or 50 mg kg(-1) BW cimetidine with a praziquantel dose of 100 mg kg(-1) BW). The fish in the sixth group were coadministered 50 mg praziquantel and 200 mg cimetidine kg(-1) BW. The fish in the control group were administered only saline. At 24 h post-treatment, the plasma was analyzed for praziquantel by reversed-phase high-performance liquid chromatography (RP-HPLC) using diazepam as the internal standard, and the gills were examined to confirm the effectiveness of each treatment. The praziquantel concentration in plasma of fish administered 100 mg praziquantel + 200 mg cimetidine kg(-1) BW was not significantly different from that of fish treated with 200 mg praziquantel kg(-1) BW and was significantly (p < 0.05) higher (about 2 times) than that of fish administered 100 mg praziquantel kg(-1) BW. The group of fish administered 50 mg praziquantel + 200 mg cimetidine kg(-1) BW showed a similar plasma praziquantel concentration to that in the fish treated with 100 mg praziquantel kg(-1) BW. The treatment efficacies of the groups of fish coadministered 100 mg praziquantel kg(-1) BW and various concentrations of cimetidine (200, 100 and 50 mg kg(-1) BW) were not significantly different from that of the group of fish administered 200 mg praziquantel kg(-1) BW, but were significantly higher than those of the groups of fish fed 100 mg praziquantel kg(-1) BW alone or coadministered 50 mg praziquantel + 200 mg cimetidine kg(-1) BW.