Pharmacokinetic study of a new 4,5-dihydroisoxazole-5-carboxamide derivative in rats

Introduction. 3-(2-butyl-5-chloro-1H-imidazole-4-yl)-N-[4-methoxy-3-(trifluoromethyl)phenyl]-4,5-dihydro-1,2-oxazole-5-carboxamide (R004) is a prospective new molecule for the treatment of rheumatoid arthritis. This compound is at the stage of preclinical research, during which its pharmacokinetics must be studied along with efficacy and safety. In this case, it is necessary to establish the main pharmacokinetic parameters of the drug and its metabolites in blood plasma after a single administration.

Aim. Evaluation of linearity of pharmacokinetics and relative bioavailability of 3-(2-butyl-5-chloro-1H-imidazole-4-yl)-N-[4-methoxy-3-(trifluoromethyl)phenyl]-4,5-dihydro-1,2-oxazole-5-carboxamide and its main metabolites in plasma after a single administration of the substance to rats.

Materials and methods. Substance R004 was administered to rats once orally at dosages of 10 mg/kg, 20 mg/kg and 40 mg/kg and intraperitoneally at a dosage of 10 mg/kg. The study was carried out using 24 Wistar rats: 6 rats were used for each of the dosage. Blood samples were collected before administration and 30 min, 1 h, 1 h, 30 min, 2 h, 3 h, 4 h, 6 h, 8 h, 10 h, 12 h, 24 h after administration of the drug. The obtained plasma was stabilized with a 250 mM ammonium acetate solution to prevent hydrolysis of R004. Plasma samples were prepared by means proteins precipitation by acetonitrile solution of internal standards. Measurement of the concentration of R004 and its metabolites 3-(2-butyl-5-chloro-1H-imidazole-4-yl)-4,5-dihydro-1,2-oxazole-5-carboxylic acid (M1) and 4-methoxy-3-(trifluoromethyl)aniline (M2) was performed using HPLC-MS/MS. A non-compartment approach was applied for evaluation pharmacokinetic parameters.

Results and discussion. The developed bioanalytical method has been fully validated in accordance with the requirements of the EAEU guideline for conducting bioequivalence study and ICH M10 guideline. The analytical range of determination in plasma of R004 was 2–2000 ng/ml, M1 and M2 – 1–1000 ng/ml. The dependence of the parameters C_max and AUC_0–t of the studied compound and its metabolites on the administered dose was linear. Thus, the value of the correlation coefficient of C_max R004 was 0.9995, and value of the correlation coefficient of AUC_0–t was 0.9991. The presence of enterohepatic recirculation R004 has been determined. The relative bioavailability of R004 was 21.26%.

Conclusion. The developed method was successfully applied for the pharmacokinetic research. R004 and its metabolites have linear pharmacokinetics in case of oral administration.

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