Pharmacokinetics of praziquantel in rainbow trout, Oncorhynchus mykiss (Walbaum 1792) following a single dose oral administration.

Abstract

This study examined the pharmacokinetics of praziquantel (PZQ) in rainbow trout (Oncorhynchus mykiss) following a single oral dose of 50 mg kg^-1 fish. Fish (average weight 107.65 ± 34.56 g; length 21.5 ± 2.30 cm) were sampled at multiple intervals (0 to 128 h post-administration). Tissue samples (liver, kidney, gill, intestine, muscle, and plasma) were analyzed using LC-MS/MS and evaluated via a Mixed-Effects Approach with Structural Models (MAS). PZQ was absorbed most rapidly in the liver, which peaked at 205 µg kg⁻¹ in 2 h and had the highest absorption rate constant (kₐ = 1.03 h⁻¹), followed by the intestine (kₐ = 0.96 h⁻¹). Muscle tissue showed the slowest absorption (kₐ = 0.134 h⁻¹) and the longest absorption half-life (t₁/₂ₐ = 5.17 h), indicating prolonged drug retention. The highest AUC₀₋128 values were found in the gill (10,233.25 µg·h/kg) and plasma (9,309.29 µg·h/kg), reflecting greater drug exposure. Elimination varied across tissues, with muscle showing the fastest elimination (kₑ = 0.052 h⁻¹) and shortest elimination half-life (13.38 h), while the intestine exhibited the longest elimination half-life (70.18 h) and mean residence time (MRT = 102.29 h), suggesting extended retention. Model fitting showed the liver data had the highest correlation (R² = 0.978) and lowest residuals (0.944). The study characterizes the pharmacokinetic profile of praziquantel in rainbow trout, demonstrating its prolonged retention in plasma and intestinal tissues. These findings support the development of targeted dosing regimens to enhance antiparasitic efficacy, minimize tissue residues, and reduce the potential for antimicrobial resistance, thereby promoting its safe and effective use in aquaculture.