Introduction Products marketed as dietary supplements for improving sexual performance at times include phosphodiesterase type 5 (PDE5) inhibitors, such as sildenafil and analogues. The ingestion of these dietary supplements is extremely dangerous as these are not evaluated for their efficacy and safety as pharmaceuticals, and their manufacture is not controlled. For this reason, regulatory authorities conduct inspections on these products to prevent the occurrence and spread of health hazards. Tadalafil is one of the PDE5 inhibitors, and its analogues are found as the most major adulterants in sexual products after analogues of sildenafil. Tadalafil has two chiral carbons that are both R configuration, which is important for PDE5 inhibitory activity. To confirm the molecular configuration of the tested compound, it is subject to instrumental analysis such as circular dichroism detection or X-ray crystal structure analysis. Therefore, it takes longer for testing tadalafil than for other compounds that do not require these processes. Meanwhile, in 2020, the product containing 120 times more tadalafil than the normal dosage was detected in Tokyo, making it an urgent issue to remove these dangerous products from the market. This study proposes a simple and rapid method to detect tadalafil with a newly devised detector tube. Objective Development of a detector tube for the rapid screening of tadalafil with simple functioning. Methods Approximately 80 mg of silica gel powder impregnated with sulfuric acid was filled in a glass tube, having a 3-mm inner diameter, to prepare a detector tube. The measuring method of this detector tube is quite simple; first, both tips of the detector tube are cut, then the sample solution is aspirated, and a decision is made by the colour of the detector tube after 5 minutes. It was defined as a positive result when the detector tube turned violet and negative when it showed other colours. First, the reaction of tadalafil and analogues were confirmed using the prepared detector tube. Then, specificity was tested for active pharmaceutical ingredients and common additives. The tube was also tested for the applicability to some commercially available dietary supplements. Results All tested tadalafil and analogues showed positive results in the test. The limit of detection was 5 μg/mL for tadalafil. Except for levomepromazine, results for additives and any pharmaceutical ingredients tested were negative. This tube was able to detect all real samples containing tadalafil and analogues. None of the real samples that did not contain tadalafil and analogues gave false positives. Conclusions The developed detector tube could rapidly detect tadalafil and analogues with high sensitivity in a simple procedure. It was suggested that false-positive results could occur only if levomepromazine was included in the sample. Other than that, no significant interference that leads to false results was observed in tested common adulterants and additives of supplements. Furthermore, the tube was able to detect tadalafil and analogues in all tested real samples. Accordingly, the proposed test method has the potential for the use of preliminary screening of tadalafil.
Sexual enhancement products adulterated with phosphodiesterase 5 inhibitors (PDE‐5i) pose a serious public health concern. Tadalafil and its analogues (Tds) are PDE‐5i frequently detected as adulterants. In this study, a Td detector tube for the rapid detection of Tds was developed based on the color change reaction between sulfuric acid and Tds. The specificity of this test method was evaluated using 13 Tds, all of which elicited positive results. Additionally, 30 commonly found adulterants in dietary supplements, 11 active pharmaceutical ingredients of psychotropic drugs and 18 food ingredients were tested and obtained no false‐positive results, except levomepromazine. The test tube accurately detected the presence or absence of Tds in 54 commercially available products. The visual detection limit was 2–50 and 5–20 μg/ml for Tds and tadalafil‐spiked samples with matrix, respectively. The applicability of the developed detector tube to a semiquantitative test using digital image analyses were investigated using red, green, and blue color values. The results of the recovery test suggested that the tube test was affected by the dark‐colored matrix. The results of semiquantitative analyses of tadalafil for five marketed products were consistent with the liquid chromatographic quantification results, except for the blue value. The detector tube developed in this study can facilitate with the rapid screening of Tds in adulterated sexual enhancement products.
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