UHPLC for Quality Evaluation of Genuine and Illegal Medicines Containing Sildenafil Citrate and Tadalafil

One of the highest incidences of illegal drug products is related to phosphodiesterase-5 inhibitors, used in treatment of erectile dysfunction, including those containing sildenafil citrate and tadalafil. In this context, comprehensive evaluation of the quality of genuine and illegal medicines was performed. A simple and rapid ultra-high performance liquid chromatography (UHPLC-UV) method to quantify sildenafil and tadalafil in the presence of six degradation products was developed and validated. Sildenafil and tadalafil were submitted to forced degradation. The separation was carried out on a Kinetex C-18 (50 x 2.1 mm; 1.7 mu m) column with mobile phase composed of acetonitrile and aqueous triethylamine solution. The calibration curves were linear in the range of 14-126 mu g mL(-1) for sildenafil citrate and 4-36 mu g mL(-1) for tadalafil and the method proved to be selective, precise, accurate and robust. Sildenafil degraded in oxidative media, whereas tadalafil degraded in acidic, alkaline and oxidative environment. The chemical structures and the mechanisms for the formation of the main degradation products were proposed by UHPLC coupled to tandem mass spectrometry. The UHPLC-UV method was applied in the pharmaceutical analysis of genuine and seized medicines. Some of them did not meet quality standards, mainly due to contents below specifications and the large variation on contents between units within a batch.

Automated summary

The high incidence of illegal drug products containing phosphodiesterase-5 inhibitors, like sildenafil and tadalafil, used for erectile dysfunction treatment, prompted a study on the quality of genuine and illegal medicines. A rapid UHPLC-UV method was developed to quantify these drugs and their degradation products. While the method proved to be accurate and selective, some seized medicines did not meet quality standards due to variations in contents between units within a batch.