Elucidation of the absolute configuration of a tadalafil analogue found as adulterant in a health supplement by mass spectrometry, chiroptical methods and NMR spectroscopy

Analytical methods for the detection and characterization of unapproved phosphodiesterase type 5 inhibitors (PDE-5i) used in adulteration of dietary supplements- a review

This article is an up-to-date review of 112 unapproved phosphodiesterase type 5 inhibitors (PDE-5i) found as adulterants in sexual enhancement dietary supplements and other products from 2003 to July 2023. Seventy-five of these unapproved PDE-5i are analogues of sildenafil (67%), followed by 26 analogues of tadalafil (23%), 9 analogues of vardenafil (8%) and 2 other type of compounds (2%). The products have been formulated in various packaging, primarily in capsule, tablet, and powder forms. Common screening techniques allowing detection of such analogues include high performance or ultra-high performance liquid chromatography in tandem with ultra-violet detector (HPLC-UV or UPLC-UV) (50%) and thin-layer chromatography in tandem with ultra-violet detection (TLC-UV) (7%). Screening by mass spectrometry (MS) is relatively less common with the use of single-, triple-quadrupole or time-of-flight (TOF) mass spectrometers (9%). Meanwhile, the combined detection by UV-MS has been recorded at 10% usage. Screening by proton nuclear magnetic resonance spectroscopy (NMR) (11%) has also been applied. For compound characterization, i.e. structural elucidation, NMR spectroscopy has been preferred (100 out of 112 compounds), followed by high-resolution mass spectrometry (HRMS) (74 out of 112 compounds) and Fourier-transform infrared spectroscopy (FTIR) (44 out of 112 compounds). Over the past two decades, analytical technology has been evolving with enhanced sensitivity and resolution. Despite this, structural elucidation of the new emerging analogues in adulterated dietary supplements remains a challenge, especially when the analogues involve complex structural modification. Therefore, the above-mentioned techniques may not be adequate to characterize the analogues. Additional work involving chiroptical methods, two-dimensional (2D) NMR experiments and X-ray crystallography are likely to be required in the future.

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.

Detection of 94 compounds related to sexual enhancement including sildenafil, tadalafil, vardenafil and their analogues in various formulations of dietary supplements and food samples using HPLC and LC-MS/MS

With an increase in the detection of structural and functional analogues of phosphodiesterase type 5 inhibitors (PDE-5i) in dietary supplements (DS) and foods, public health is threatened. Some products advertise natural ingredients despite containing PDE-5i that can cause serious adverse effects on human health. To avoid detection during routine screening, novel PDE-5i have been synthesised and added to DS and foods. The purpose of this study was to detect, identify, and quantify 94 PDE-5i and related compounds in DS and foods. Furthermore, the study investigated the detection cases and compared them by sample type, formulation, and compounds. The HPLC and LC-MS/MS methods were validated for limit of detection (LOD), limit of quantification (LOQ), linearity, and recovery in solid and liquid type samples. Both HPLC and LC-MS/MS showed satisfactory results, which were in conformance with the ICH guidelines. A total of 404 samples, including DS (99), and foods (305) were purchased from online and offline markets. Samples divided into 5 types of formulation were analysed; tablet, capsule, pilula (herbal medicine pill), powder and liquid type. Of these 130 samples (47 of 99 DS, and 83 of 305 foods) contained one or more PDE-5i or related compounds. Among the five types of formulation, the tablet type showed the highest detection rate (61.1%) in DS, whereas the capsule type showed the highest detection rate (53.8%) in food samples. This study will be helpful for monitoring illegal ED-related products, providing information to consumers, and ultimately contributing to protecting public health.