Pharmacokinetic profile of a single intramuscular or oral dose of meloxicam in red kangaroos (Osphranter rufus).

Abstract

Objective: Determine pharmacokinetic parameters of meloxicam in red kangaroos following a single IM or PO dose.

Methods: In the spring of 2024, following a pilot study to determine the appropriate dosage, a managed population of clinically healthy adult or subadult red kangaroos at the Nashville Zoo received a 0.2-mg/kg dose of meloxicam, IM or PO. Four additional kangaroos received a 0.2-mg/kg dose of meloxicam, IV, to establish bioavailability. Blood samples were obtained under manual restraint over 48 hours, using a sparse sampling method. Plasma meloxicam concentration was determined using HPLC. Plasma meloxicam time-concentration profiles were established using a non-compartmental pharmacokinetic analysis.

Results: 15 kangaroos were included in this study. Eight kangaroos were assigned to the IM group, and 8 were assigned to the PO group. Pharmacokinetic parameters were time to the maximum observed plasma concentration (tmax) = 0.5 hours, maximum plasma concentration (Cmax) = 1.071 μg/mL, terminal half-life (t½) = 13.03 hours, elimination rate constant (λz) = 0.05 1/h, area under the plasma concentration-versus-time curve from time 0 to last point (AUC0-last) = 11.643 h·μg/mL, area under the plasma concentration-versus-time curve from time 0 to infinity (AUC0-∞) = 12.460 h·μg/mL, bioavailability = 129%, and apparent volume of distribution after extravascular administration (V/F) = 234 mL/kg, and tmax = 6 hours, Cmax = 0.445 μg/mL, t1/2 = 9.90 hours, λz = 0.07 1/h, AUC0-last = 6.666 h·μg/mL, AUC0-∞ = 7.023 h·μg/mL, bioavailability = 73%, and V/F = 557 mL/kg for the IM and PO groups, respectively. One kangaroo collapsed and died approximately 15 minutes following administration of an IV dose of meloxicam. Necropsy revealed intracranial hemorrhage.

Conclusions: The Cmax and t1/2 of meloxicam were greater in the IM group than the PO group. When dosed IM, plasma meloxicam concentrations reached levels reported to be therapeutic in other species, while this was inconsistently achieved with PO dosing.

Clinical relevance: IM meloxicam may offer advantages to PO dosing due to the greater Cmax and longer t1/2. Nonsteroidal anti-inflammatory drugs are known to decrease platelet function, and it is unknown if red kangaroos are at increased risk for hemorrhage following the administration of meloxicam compared to other species.