Pharmacokinetic evaluation of meloxicam following intravenous and intramuscular administration in Crocodylus siamensis, a freshwater crocodile

The pharmacokinetics of meloxicam (MLX) remain largely unexplored in reptiles, particularly in Siamese crocodiles (Crocodylus siamensis). This study characterized the pharmacokinetic profiles of MLX following intravenous (IV) and intramuscular (IM) administration in Siamese crocodiles. Fifteen Siamese crocodiles were divided into three groups (n=5) using a randomization procedure according to a parallel study design. MLX was administered IV at 0.2 mg/kg b.w. or IM at two different doses (0.2 mg/kg b.w. or 0.4 mg/kg b.w.). Plasma concentrations of MLX were measured using a validated high-performance liquid chromatography method with UV detection. The pharmacokinetic parameters were analyzed using a non-compartment model. The elimination half-life (t_1/2λz) was long for all administration routes, with values of 132.34 hr (IV), 121.35 hr (IM 0.2 mg/kg b.w.), and 181.44 hr (IM 0.4 mg/kg b.w.). The volumes of distribution (Vd) and clearance (Cl) after IV administration were 104.59 mL/kg and 0.55 mL/hr/kg, respectively. Based on these results, there was an extended t_1/2λz of MLX in this species of freshwater crocodiles, highlighting significant differences in drug disposition compared to other reptilian and non-reptilian species. The findings contribute to an understanding of MLX pharmacokinetics in this animal species, and emphasize that the selection of the optimal dose of MLX should be considered based on disposition kinetics, efficacy, safety, and species-specific differences. Further investigation is required to identify the effective plasma concentration, which is critical for establishing the appropriate dose for the management of pain and inflammation.