HPLC Quantification and Impurity Profiling of Counterfeit Sildenafil Tablets from the African Market
Abstract
Counterfeit medicines represent a major public health concern, as they may contain toxic substances, inappropriate excipients, or incorrect amounts of the active pharmaceutical ingredient (API), including cases with no API at all, despite being marketed as authentic. This study aimed to quantify sildenafil citrate and identify impurities in illegally distributed products. Nine counterfeit sildenafil citrate tablets (labeled 100 mg) were analyzed by high-performance liquid chromatography (HPLC). Separation was achieved on a Lycospher C18 column (15 cm × 4.6 mm, 5 μm) using 0.2 M ammonium acetate buffer (pH 7.0) and acetonitrile (50:50, v/v) as the mobile phase, at a flow rate of 1 mL/min, injection volume 20 μL, and UV detection at 240 nm. The method provided reliable separation of sildenafil and related substances within a 7-minute run and was validated for linearity, recovery, precision, and limits of detection (LOD) and quantification (LOQ). Analysis showed that 44 % and 77 % of samples contained sildenafil citrate levels below USP and EP specifications, respectively. Four samples exceeded the pharmacopoeial limits for impurity B, and two exceeded the limits for impurity C. These results highlight the poor quality of counterfeit sildenafil citrate products available outside official distribution channels and underline their potential risks to patient health.
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