The evaluation of pharmacokinetic parameters of 4-(5-methyl-1,3,4-oxadiazole-2-yl)-benzenesulfonamide and its metabolites in rat plasma

Introduction: 4-(5-methyl-1,3,4-oxadiazole-2-yl)-benzenesulfonamide (ODASA) is a new pharmacologically activecompound, which is capable of reducing intraocular pressure by inhibiting carbonic anhydrase II. It is necessary to calculate the pharmacokinetic parameters of this compound and its metabolites in blood plasma of laboratory animals during a preclinical study. Aim: Evaluation of pharmacokinetic parameters of ODASA and its metabolites in rat bloodplasma after instillation of ocular suspension and its intraperitoneal administration. Materials and Methods: The study was conducted on 2 groups of Wistar rats, each including 6 individuals. The firstgroup underwent instillation of 1% ocular suspension of ODASA of 20 µL into each eye (1.6 mg/kg). The drug was injected intraperitoneally at the same dose to the second group. Blood sampling was performed before the administration,0.5h, 1h, 2h, 4h, 6h, 8h, 12h, 24h, 48h, 72 h, 96h, 120h, 144h, 192h, 240h, 288h after the administration. Plasma was immediately stabilized by 10% solution of ascorbic acid and frozen to a temperature no higher than -70°C. The sampleswere analyzed using the HPLC-MS/MS method. Chromatographic separation was performed on a Kinetex Phenyl Hexylcolumn (50*4.6 mm, 2.6 microns) in a gradient mode. Detection was carried out in the MRM mode using electrosprayionization. Results: The developed method was validated in the range of 2-2000 ng/mL for ODASA and 4-[5-(hydroxymethyl)-1,3,4-oxadiazole-2-yl]-benzenesulfonamide (M1) and 0.5 -500.0 ng/mL for N-hydroxy-4-(5-methyl-1,3,4-oxadiazole-2-yl)-benzenesulfonamide (M2). The size of the maximum plasma concentration after instillation of ODASA into eyes was 349.85±62.50 ng/mL, in M1 – 30.91±6.00 ng/mL and in M2 – 2.70±0.62 ng/mL (M±SEM). The half-life time of ODASA after ocular administration was 46.4±3.8 h, M1 – 70.0±14.3 h, and M2 - 36.5±15.2 h (M±SEM). The relative bioavailability of ODASA compared with injection was 81.03%. Conclusion: The performed validation of the method guaranteed the accuracy of the obtained results. The activesubstance has a high relative bioavailability after instillation into eyes. M1 is a major metabolite, and M2 is a minormetabolite. The studied compounds had a long half-life.