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 C18 (50 × 2.1 mm; 1.7 µm) column with mobile phase composed of acetonitrile and aqueous triethylamine solution. The calibration curves were linear in the range of 14-126 µg mL-1 for sildenafil citrate and 4-36 µg 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.

Comparison between counterfeit and authentic medicines: A novel approach using differential scanning calorimetry and hierarchical cluster analysis.

Erectile dysfunction medicines such as Cialis and Viagra are very popular worldwide and are between the most prevalent counterfeit medicines in Brazil. A range of analytical methods has been used to analyze Cialis and Viagra, such as ATR-FTIR, GCMS and UPLC-MS. Until now, there are no data available of DSC methods for analysis of counterfeit medicines of Cialis and Viagra. DSC is a thermal analysis that provides useful information of physico-chemical events, and however is almost not used for forensic purposes. In this study, thermal analysis of 25 counterfeit Viagra and Cialis seized by Brazilian Federal Police were performed by DSC and compared to their authentic medicines and analytical standards, along with chemometric tools. Authentic samples of Viagra displayed a similar thermal profile with the API, while Cialis were different with additional endothermic peaks, that could be related to excipients interference. Thermograms of Viagra counterfeit samples were similar to authentic samples, while Cialis showed an enlargement and displacement of endothermic peaks. Also, some Cialis counterfeit samples showed melting peaks attributed to sildenafil, the API of Viagra, instead tadalafil, confirming previous results obtained by UPLC-MS. Multivariate analysis with application of Hierarchical Cluster Analysis classified different groups of samples, including a cluster with counterfeit Cialis and Viagra, indicating the use of same API for both counterfeit medicines and possibly the same illicit production; and a cluster with authentic Viagra and counterfeit Cialis, confirming the addition of sildenafil instead tadalafil to Cialis counterfeit samples. Here for the first time we described the use of DSC for chemical profiling of Cialis and Viagra and showed that even when applied to a small group of samples, DSC along with chemometric tools can be considered as a good auxiliary method in forensic casework samples. DSC provided useful data to perform the identification of counterfeit and authentic medicines, with low cost and a simple method.