Screening of Indian aphrodisiac ayurvedic/herbal healthcare products for adulteration with sildenafil, tadalafil and/or vardenafil using LC/PDA and extracted ion LC–MS/TOF

Abstract

Ayurvedic/herbal healthcare products are considered safe under the impression that they are derived from natural products. But recently, there have been several reports worldwide on the adulteration of synthetic PDE-5 inhibitors in aphrodisiac herbal formulations. Therefore, the objective of the present study was to explore the presence of synthetic PDE-5 inhibitors (sildenafil, tadalafil and/or vardenafil) in ayurvedic/herbal healthcare products sold in Indian market for aphrodisiac/related uses. In total, 85 herbal formulations (HFs) were included in the study. The formulations were extracted with methanol and subjected to centrifugation. The supernatant was analysed by HPLC and LC–MS/TOF. Early detection of the presence of sildenafil, tadalafil and vardenafil in the herbal samples was done by the study of extracted ion mass chromatograms at the m/z values of respective parent ions, and two prominent fragments of each. In case of sildenafil and tadalafil, adulteration was also detected by comparing the relative retention times (RR_T) and UV spectra. Further substantiation was done through comparison of accurate mass spectra with those of the two available standards. Of the 85 HFs tested, only one was eventually found to be adulterated with sildenafil. The extent of adulterant in this sample was determined to the therapeutic dose in the formulation. The study thus indicates emergence of the problem of adulteration of Indian herbal products with PDE-5 inhibitors.

Introduction

Herbal formulations (HFs) are popular worldwide due to the belief that they are safer than synthetic drugs. However, nowadays, HFs have not remained trustworthy as lots of evidence are coming into literature about adulteration of these products with synthetic drugs or their congeners, in order to enhance the claims stated on the label. This poses a health threat to patients who unwittingly consume a compound which may be untested for safety [1], [2], [3], [4].

The reports on adulteration of HF with synthetic phosphodiaesterase-5 (PDE-5) inhibitors have been most common in recent past. The three approved inhibitors for the treatment of penile erectile dysfunction (ED), viz., sildenafil citrate (Viagra, Pfizer), tadalafil (Cialis, Elli Lilly) and vardenafil hydrochloride (Levitra, Bayer), have many documented side effects and are required to be used under medical supervision [5]. Around 60–70% cases of ED occur in patients with hypertension and ischemic heart disease, and unfortunately PDE-5 inhibitors show negative pharmacodynamic interactions with the drugs indicated for these diseases, e.g., nitroglycerine, doxazosin and terazosin [6]. Hence these ED drugs are not advised for such patients. Unfortunately, those using HF may be at risk, if there is clandestine adulteration with synthetic PDE-5 inhibitors.

There are various reports from US, China, Taiwan, Singapore, Thailand, Korea, Hong Kong, etc. on adulteration of HFs (available in local markets or purchased covertly over the internet) with PDE-5 inhibitors [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. India is a big pharmaceutical market and is also on rising graph in terms of sale and exports of HF. Most of the reports on Indian HFs mainly focus on excessive contents of toxic heavy metals [23], [24], however, no study is yet known on the status of adulteration of Indian HFs with synthetic PDE-5 inhibitors. So the objective of the present study was to investigate the Indian produced HFs for the adulteration with sildenafil, tadalafil and/or vardenafil. A recently reported strategy involving LC/PDA and LC–MS studies [25] was employed, with additional emphasis on the study of extracted ion chromatograms (EICs). The results on 85 aphrodisiac HFs are discussed in this report.