Development and validation of method for quantitative determination of sildenafil and n-desmethyl sildenafil by HPLC-MS/MS in human blood plasma

Abstract

Aim. To assess bioequivalence of sildenafil citrate tablet formulation produced by pharmaceutical company “Microkhim” (Rubezhnoe, Ukraine) it was developed and validated a prompt, specific and quite simple method for quantitative determination of sildenafil and its active metabolite - N-desmethyl sildenafil concentrations in the human blood using deuterium labeled internal standards. Direct liquid-liquid extraction procedure was utilized to extract the analytes from the blood plasma.

Methods. Contents of sildenafil and its metabolite in supernatant were determined by means of the high performance liquid chromatography / tandem mass spectrometric detection technique. Ionization of sildenafil, N-desmethyl sildenafil, sildenafil-d8 and N-desmethyl sildenafil-d8 was performed in the positive electrospray mode (ESI, Positive). Detection of the analytes was carried out in the multi reactions monitoring (MRM) regimen with the following m/z values for selected parent ions: 475,30; 483,20; 461,20 and 469,20, respectively. The daughter ion m/z value was selected to be 283,10 for all analytes.

Results. Analytical method proposed proved to demonstrate reliable accuracy and reproducibility for both analytes and has been validated within linear range 5,05-1009,92 ng/ml for sildenafil and 2,24-400,84 ng/mL for N-desmethyl sildenafil with correlation coefficient (r2) equaled to 0.9975 and 0.9973, respectively.

Conclusions. It was developed and validated a simple, specific and sensitive HPLC-MS/MS method for quantitative determination of sildenafil and its active metabolite N-desmethyl sildenafil concentrations in human blood plasma utilizing stable isotope labeled internal standards – deuterated sildenafil-d8 and N-desmethyl sildenafil- d8. Important feature of the method was a modified preanalytical procedures of biological samples preparation – direct liquid-liquid extraction that allowed to avoid laborious and time-consuming procedures such as evaporation to concentrate the samples with consequent recovery of dry residue, as well as to refuse from expensive solid-phase extraction. Application of the deuterium labeled internal standards allowed to suppress a biological matrix effect drastically, as well as to reach target LLOQ level. Experimental data obtained in the course of full validation of the method proposed that was performed in accordance with approved national and international technical and regulatory requirements, allowed to affirm high specificity, sensitivity, accuracy, reproducibility and efficiency of the method.