Pharmacokinetics and pharmacodynamics of A77 1726 and leflunomide in domestic cats

The pharmacokinetics and pharmacodynamics of A77 1726 and leflunomide after intravenous (i.v.) and oral (p.o.) administration were evaluated in adult cats. Three treatments were administered: a single i.v. dose of A77 1726 (4mg/kg), a single oral dose of leflunomide (4mg/kg), and multiple oral doses of leflunomide (2mg/kg). Mean pharmacokinetic parameter values after a single i.v. dose of A77 1726 were distribution (A) and elimination (B) intercepts (15.2μg/mL and 34.5μg/mL, respectively), distribution and elimination half-lives (1.5 and 71.8h, respectively), area under the curve (AUC _0→∞; 3723μg*h/mL), mean residence time (MRT; 93h), clearance (Cl _obs; 1.1mL/kg/h), and volume of distribution at steady state (Vd _ss; 97mL/kg). Mean pharmacokinetic parameter values after a single oral dose of leflunomide were absorption and elimination rate constants (0.3 1/h and 0.01 1/h, respectively), absorption and elimination half-lives (2.3 and 59.1h, respectively), AUC _0→∞ (3966μg*h/mL), and maximum observed plasma concentration (C _max; 38μg/mL). The bioavailability after a single oral dose of leflunomide was 100%. The mean±SD A77 1726 concentration that inhibited 50% lymphocytes (EC ₅₀) was 16±13.5μg/mL. The mean±SD maximum A77 1726 concentration (EC _max) was 61.0±23.9μg/mL.