This study investigated the pharmacokinetics of robenacoxib after administration to healthy cats IV (2 mg/kg), SC (2 mg/kg), and PO (6 mg/cat) using different feeding regimens (food withheld, one-third ration, and entire ration fed). Clearance from blood after IV administration was low (0.44 L/kg/h) with a terminal half-life of 1.5 hours (comparable to ketoprofen but markedly shorter than carprofen or meloxicam). This study identified an extraction ratio of 0.05, the minimum value for which an orally administered drug can have efficacious bioavailability.

Bioavailability after SC injection was 69%, and median time to maximum concentration (Tmax) was 1 hour. In cats with food withheld, bioavailability was 49% with Tmax of 1 hour. In contrast, cats fed their entire ration had a bioavailability of 10% and Tmax of 30 minutes. Feeding the entire ration led to decreased bioavailability and marked variation in absorption patterns.

Robenacoxib is a selective inhibitor of COX-2 with minimal effect on COX-1. In this study, in cats fed all 3 feeding regimens, there was marked inhibition of COX-2 seen at the median time to Tmax, with only minimal and transient inhibition of COX-1. Optimal efficacy of robenacoxib is expected with SC or IV administration or PO in cats from which food is withheld or provided one-third of ration. Study supported by Novartis Animal Health

Commentary
The NSAID robenacoxib (Onsior) is available in the United States as an oral tablet for use in cats. Currently, the labeled directions to treat acute postoperative pain and inflammation in cats are 1 mg/kg PO q24h for up to 3 days. A common concern with any oral medication is whether meals can interfere with drug absorption and overall effective plasma bioavailability. This study was undertaken to further define the pharmacokinetics of robenacoxib in healthy cats after PO administration with and without a meal as compared with parenteral administration. The results should prove valuable for the practicing veterinarian when counseling clients about postoperative robenacoxib use.—Andrew Claude, DVM, DACVAA

Source
Effects of route of administration and feeding schedule on pharmacokinetics of robenacoxib in cats. King JN, Jung M, Maurer MP, et al. Am J Vet Res 74:465-472, 2013.