Pharmacokinetics of praziquantel in gilthead seabream (Sparus aurata) plasma and gills

The pharmacokinetics (PKs) of dietary administered praziquantel (PZQ) were determined in gilthead seabream (Sparus aurata), the most commercialized marine farmed fish species in the Mediterranean area. Gilthead seabreams weighting 52 g were given a single dietary dose of either 75 or 150 mg/kg fish at 21 °C. The low dosing was also intravascularly (i.v) injected to assist the calculation of drug bioavailability (F). Plasma and gill samples were measured on 1, 2, 4, 6, 8, 12, 24, 48, 72, and 96 h post-administration. PZQ was rapidly absorbed in fish circulation as the maximum plasma concentration was achieved as early as 4 h (6.7 μg/mL) and 6 h post-administration (8.2 μg/mL), for the low and high dosing, respectively. The two-fold increase in dosing led to significant differences during the first six hours post administration, while the highest increase was <50%. The advantage of the higher dosing schedule was also apparent in PZQ measurements in gills, where maximum drug levels were measured to be 20.7 and 39.1 μg/g at 75 and 150 mg/kg fish, respectively. Albeit, plasma elimination half-life (t1/2β) was shorter at high (14.4 h) compared to that calculated for the low PZQ dosing (25.7 h), depletion of PZQ from all gilthead seabream tissues examined was considered rapid at both dosing regimens. The F of PZQ was calculated to be 49%, confirming a high absorption in fish circulation. Due to the clearance pattern and the rapid removal of PZQ from fish circulation, daily dosing should be divided into two medicated meals, to ensure adequate drug circulatory levels during treatment. Overall, PZQ is readily bioavailable in gilthead seabream while the dosing of 150 mg/kg fish is preferable resulting in higher circulatory and gill levels compared to the low dose tested.