Transdermal administration of flunixin meglumine results in systemic absorption in southern white rhinoceros (Ceratotherium simum simum).

OBJECTIVE

To assess the pharmacokinetics of a single application of transdermal flunixin meglumine in southern white rhinoceros (Ceratotherium simum simum).

METHODS

Healthy adult white rhinoceros were prospectively enrolled in the study from June through September 2024. Baseline blood samples were collected prior to drug administration. A single (3.3 mg/kg) dose of commercially available transdermal flunixin meglumine was applied topically at 2 primary sites: the nuchal hump extending behind the ears and the skin overlying the spine from the shoulder to ischium. Blood samples were collected under behavioral restraint at 2 to 4 time points for each rhinoceros following a sparse-sampling model. Drug assay validation and plasma drug concentrations were determined using HPLC-MS-MS.

RESULTS

Successful application of transdermal flunixin meglumine was achieved in 13 individuals. Twelve individuals were included in compartmental analysis. The time to maximum plasma concentration was 7.2 hours. The peak plasma concentration was 0.31 μg/mL. The elimination half-life was 28.6 hours. Mild behavioral changes were observed in 6 animals and included quiet mentation, rubbing at the application site, lethargy, and mild ataxia. All side effects were noted to be resolved 24 hours after drug application.

CONCLUSIONS

Transdermal flunixin meglumine was absorbed and measurable plasma concentrations achieved in all southern white rhinoceros. The side effects observed included short-duration behavioral changes.

CLINICAL RELEVANCE: This study reports successful use and pharmacokinetic parameters of transdermal flunixin meglumine at 3.3 mg/kg when applied to the neck and topline in southern white rhinoceros.