Pharmacokinetics of the novel COX-2 selective inhibitor vitacoxib in cats: The effects of feeding and dose

Pharmacokinetics, Tissue Distribution, Metabolism and Excretion of a Novel COX-2 Inhibitor, Vitacoxib, in Rats

The objectives of this study were to elucidate absorption, tissue distribution, excretion, and metabolism of vitacoxib, a novel selective cyclooxygenase-2 inhibitor, in Wistar rats. Vitacoxib was detected in most tissues within 15 min, suggesting that it was well distributed. Moreover, it could cross the intestinal barrier. Vitacoxib was mainly eliminated as two metabolites. Nine proposed metabolites of vitacoxib were found in the plasma, bile, urine, and feces of rats. Two main metabolites, 4-(4-chloro-1-(5-(methyl-sulfonyl) pyridin-2-yl)-1H-imidazol-5-yl) phenyl methanol (M1) and 4-(4-chloro-1-(5-(methyl-sulfonyl) pyridin-2-yl)-1H-imidazol-5-yl) benzoic acid (M2), were identified in rat feces and urine. Further, the authentic standards of M1 and M2 were synthesized to confirm their structures. The carboxylic acid derivative was the major metabolite of vitacoxib excreted in the urine and feces. Hydroxylation of the aromatic methyl group of vitacoxib and additional oxidation of the hydroxymethyl metabolite to a carboxylic acid metabolite were the proposed metabolic pathways. Vitacoxib displayed a high AUC_last (4895.73 ± 604.34 ng·h/ml), long half-life (4.25 ± 0.30 h), slow absorption (T_max, 5.00 ± 2.00 h), and wide tissue distribution in rats. Our findings provide significant information for the further development and investigation of vitacoxib as an effective nonsteroidal anti-inflammatory agent, and highly its potential for use future in a clinical setting.

Non-Linear Mixed-Effects Pharmacokinetic Modeling of the Novel COX-2 Selective Inhibitor Vitacoxib in Cats

The objective of this study was to develop a non-linear mixed-effects (NLME) model to describe the disposition kinetics of vitacoxib in cats following intravenous (I.V) and oral (P.O) (single and multiple) dosing. Data from six consecutive studies with 16 healthy neutered domestic short hair cats were pooled together to build a pharmacokinetic (PK) model using NLME. Population PK parameters were estimated using the stochastic approximation expectation maximization (SAEM) algorithm implemented in Monolix 2019R2. A two-compartment mammillary disposition model with simultaneous zero- and first-order absorption best described the PK of vitacoxib in plasma after oral dosing. The systemic CL of vitacoxib was found to be low (110 ml/h), with a steady-state volume of distribution (VSS) of 3.42 L in cats. Results from the automated covariate search in Monolix 2019R2 showed that bodyweight had a significant effect on the central volume of distribution of vitacoxib. Lastly, using Monte Carlo simulations, we investigated the time course of several dosages of vitacoxib from 0.01 to 8 mg/kg. Using this simulation set, we found a range of reasonable dosages that produce therapeutic plasma concentrations of vitacoxib for 24 h or more in cats.

Pharmacokinetics of three formulations of vitacoxib in horses

The pharmacokinetic properties of three formulations of vitacoxib were investigated in horses. To describe plasma concentrations and characterize the pharmacokinetics, 6 healthy adult Chinese Mongolian horses were administered a single dose of 0.1 mg/kg bodyweight intravenous (i.v.), oral paste, or oral tablet vitacoxib in a 3-way, randomized, parallel design. Blood samples were collected prior to and at various times up to 72 hr postadministration. Plasma vitacoxib concentrations were quantified using UPLC-MS/MS, and pharmacokinetic parameters were calculated using noncompartmental analysis. No complications resulting from the vitacoxib administration were noted on subsequent administrations, and all procedures were tolerated well by the horses throughout the study. The elimination half-life (T_1/2λz ) was 4.24 ± 1.98 hr (i.v.), 8.77 ± 0.91 hr (oral paste), and 8.12 ± 4.24 hr (oral tablet), respectively. Maximum plasma concentration (C_max ) was 28.61 ± 9.29 ng/ml (oral paste) and 19.64 ± 9.26 ng/ml (oral tablet), respectively. Area under the concentration-versus-time curve (AUC_last ) was 336 ± 229 ng hr/ml (i.v.), 221 ± 94 ng hr/ml (oral paste), and 203 ± 139 ng hr/ml, respectively. The results showed statistically significant differences between the 2 oral vitacoxib groups in T_max value. T_1/2λz (hr), AUC_last (ng hr/ml), and MRT (hr) were significantly different between i.v. and oral groups. The longer half-life observed following oral administration was consistent with the flip-flop phenomenon.

Nonlinear mixed-effects pharmacokinetic modeling of the novel COX-2 selective inhibitor vitacoxib in dogs

The objective of this study was to develop a nonlinear mixed-effects model of vitacoxib disposition kinetics in dogs after intravenous (I.V.), oral (P.O.), and subcutaneous (S.C.) dosing. Data were pooled from four consecutive pharmacokinetic studies in which vitacoxib was administered in various dosing regimens to 14 healthy beagle dogs. Plasma concentration versus time data were fitted simultaneously using the stochastic approximation expectation maximization (SAEM) algorithm for nonlinear mixed-effects as implemented in Monolix version 2018R2. Correlations between random effects and significance of covariates on population parameter estimates were evaluated using multiple samples from the posterior distribution of the random effects. A two-compartment mamillary model with first-order elimination and first-order absorption after P.O. and S.C. administration, best described the available pharmacokinetic data. Final parameter estimates indicate that vitacoxib has a low-to-moderate systemic clearance (0.35 L hr^-1  kg^-1 ) associated with a low global extraction ratio, but a large volume of distribution (6.43 L/kg). The absolute bioavailability after P.O. and S.C. administration was estimated at 10.5% (fasted) and 54.6%, respectively. Food intake was found to increase vitacoxib oral bioavailability by a fivefold, while bodyweight (BW) had a significant impact on systemic clearance, thereby confirming the need for BW adjustment with vitacoxib dosing in dogs.