Robenacoxib pharmacokinetics in sheep following oral, subcutaneous, and intravenous administration

Pharmacokinetics of robenacoxib following single intravenous, subcutaneous and oral administrations in Baladi goats (Capra hircus)

The purpose of this study was to assess the pharmacokinetics of robenacoxib (RX), a COX-2 selective non-steroidal anti-inflammatory drug, in goats after single intravenous (IV), subcutaneous (SC) and oral (PO) administrations. 5-month-old healthy female goats (n = 8) were used. The animals were subjected to a three-phase, two-dose (2 mg/kg IV, 4 mg/kg SC, PO) unblinded, parallel study design, with a four-month washout period between the IV and SC treatment, and a one-week period between the SC and PO treatment. Blood was drawn from the jugular vein in heparinized vacutainer tubes at 0, 0.085 (for IV only), 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10 and 24 h. Plasma RX concentrations were measured using HPLC coupled to a UV multiple wavelength detector, and the data were pharmacokinetically analysed using ThothPro™ 4.3 software in a non-compartmental approach. Following IV administration, terminal elimination half-life, volume of distribution and total clearance were 0.32 h, 0.24 L/kg and 0.52 L/h/kg, respectively. For SC and PO, the mean peak plasma concentrations were 2.34 and 3.34 μg/mL at 1.50 and 0.50 h, respectively. The t1/2λz was significantly different between the IV and the extravascular (EV) administrations (0.32 h IV vs 1.37 h SC and 1.63 h PO), suggesting the occurrence of a flip-flop phenomenon. The significant difference in Vd values between IV (0.24 L/kg) and EV (0.95 L/kg SC and 1.71 L/kg; corrected for F %) routes might have also triggered the t1/2λz difference. The absolute average SC and PO bioavailability were high (98% and 91%, respectively). In conclusion, the IV administration of RX might not be suitable for goats, due to its short t1/2λz. The EV routes, however, appear to be convenient for the drug's occasional use.

Disposition kinetics of robenacoxib following intravenous and oral administration in geese (Anser anser domesticus)

Robenacoxib (RX) is a veterinary cyclooxygenase-2 selective inhibitor drug. It has never been tested on birds and is only labelled for use in cats and dogs. The purpose of this study was to assess its pharmacokinetics in geese after single intravenous (IV) and oral (PO) administrations. Four-month healthy female geese (n = 8) were used. Geese were subjected to a two-phase, single-dose (2 mg/kg IV, 4 mg/kg PO), open, longitudinal study design with a four-month washout period between the IV and the PO phases. Blood was collected from the left wing vein to heparinized tubes at 0, 0.085 (for IV only), 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10, and 24 h. Plasma RX concentrations were measured using HPLC coupled to an UV detector, and the data were pharmacokinetically analysed using ThothPro™ 4.3 software in a non-compartmental approach. Following IV administration, terminal elimination half-life, volume of distribution, and total clearance were 0.35 h, 0.34 L/kg, and 0.68 L/h/kg, respectively. For the PO route, the mean peak plasma concentration was 6.78 μg/mL at 0.50 h. The t1/2λz was very short and significantly different between the IV and PO administrations (0.35 h IV vs. 0.99 h PO), suggesting the occurrence of a flip-flop phenomenon. The Cl values corrected for the F% were significantly different between IV and PO administrations. It might have been a consequence of the longitudinal study design and the altered physiological and environmental conditions after a 4-month washout period. The absolute oral F% computed with the AUC method surpassed 150%, but after normalizing it to t1/2λz, it was 46%. In conclusion, the administration of RX might not be suitable for geese, due to its short t1/2λz.

Examination of the pharmacokinetics and differential inhibition of cyclooxygenase isoenzymes in New Zealand white rabbits (Oryctolagus cuniculus) by the Non-Steroidal anti-inflammatory Robenacoxib

Effective rabbit analgesia is challenging, and there are few studies available on the newer COX-2 selective NSAIDs, such as robenacoxib. This study aimed to establish the pharmacokinetics of oral and subcutaneous robenacoxib, describe its inhibitory actions on COX enzymes, and develop dosing, using six healthy New Zealand white rabbits. Pharmacokinetics were determined from plasma concentrations after oral administration of robenacoxib (0.83-0.96 mg/kg) and also after subcutaneous administration (2 mg/kg). The inhibitory actions of robenacoxib were evaluated by measuring plasma concentrations of thromboxane B₂ (TBX₂ ) and prostaglandin E₂ (PGE₂ ) as surrogate markers of cyclooxygenase enzyme isoform inhibition. The mean maximum concentration for oral and subcutaneous administration was 0.23 μg/ml and 5.82 μg/ml, respectively. Oral robenacoxib administration did not demonstrate a significant difference between any time point for PGE₂ or TBX₂ , though subcutaneous administration did for both. There was no significant difference in PGE₂ or TBX₂ concentrations at any time point when comparing subcutaneous versus oral routes. Although the results support that plasma robenacoxib exceeds the therapeutic levels compared to dogs and cats, there was little significance in the difference in the changes associated with COX-1 and COX-2 inhibition. Further studies are warranted to determine appropriate dosing, safety, and efficacy in rabbits.

Synopsis of the pharmacokinetics, pharmacodynamics, applications, and safety of firocoxib in horses

According to in vitro and in vivo investigations, firocoxib (FX), a second-generation coxib, is a highly selective COX-2 inhibitor in horses. With a COX-1/COX-2 IC₅₀ ratio of 643 in horses, FX spares the COX-1 inhibitory effects. It is approved for the treatment of musculoskeletal problems and lameness in horses and dogs with osteoarthritis (OA). For the treatment of OA in horses, both an injectable formulation for IV administration at a dose of 0.09 mg/kg for five days and an oral paste formulation at a dose of 0.1 mg/kg for 14 days are licensed. Numerous analytical methods were reported in the literature to quantify FX in biological fluids, using HPLC and LC-MS. FX presents remarkable pharmacokinetics and pharmacodynamics compared to other coxibs. It has an oral bioavailability of 80% or higher and is effectively absorbed by horses. Its volume of distribution is around 2 L/kg, and it is slowly eliminated. Due to the long elimination half-life (around 2 days), which allows a once daily dosing, a single 0.3 mg/kg loading dose has been recommended. This enables the establishment of steady-state drug concentrations within 24 h, making it appropriate for acute treatment as well. Its IC₈₀ is equal to 103 ng/mL in whole blood and, with an EC₅₀ of 27 ng/mL, it has the highest affinity for its receptor compared to the other commonly administered NSAIDs in horses.