Evaluation of heavy metal impurities in metformin tablet brands marketed in Ilorin, Nigeria

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Faculty of Pharmaceutical Sciences, University of Ilorin


The safety and quality of pharmaceutical products are important considerations for optimal therapeutic outcomes. Periodic assessment of heavy metals impurities in pharmaceutical products used for long- term treatment of chronic diseases is important to safeguard the health and well-being of patients. This study investigated the levels of manganese (Mn), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in brands of metformin tablets commonly prescribed in Ilorin, Nigeria, for the management of diabetes. Five brands of commonly prescribed metformin tablets were randomly purchased from pharmacies in Ilorin, North-central Nigeria. Metal concentrations in the acid digested samples were profiled using Atomic Absorption Spectrophotometry (AAS) method. Method validation results showed excellent linearity (r2=0.9921(Mn), 0.9995 (Cu), 0.9998 (Zn), 0.9996(Cd), 0.9913(Pb)), with limits of detection (0.001, 0.001, 0.002, 0.002 and 0.025 mg/L for Mn, Cu, Zn, Cd and Pb respectively) and limits of quantification (0.003, 0.003, 0.006, 0.006 and 0.076 mg/L for Mn, Cu, Zn, Cd and Pb respectively) in the concentration ranges of 2– 10, 0.2–1.6, 0.2–1.6, 1–4 and 1–4 mg/L for Mn, Cu, Zn, Cd and Pb respectively. Mn, Cu, and Zn were detectable in varying concentrations in all the five brands of metformin evaluated in this study while none of the brands contained Cd and Pb at detectable levels. The levels of Mn, Cu and Zn ranged between 0.031-0.062, 0.085-0.112 and 0.040-0.130 mg/mL respectively across the brands. The highest concentrations of Mn, Cu and Zn were 0.062(0.001), 0.112(0.001) and 0.130(0.001) mg/L respectively. Similarly, maximum daily ingestible amounts for Mn, Cu and Zn ranges between 0.84-1.75, 2.17-3.03 and 6.12-20.7 μg/day respectively, which were below permissible daily exposure (PDE). These results indicate that all the metformin brands evaluated could be safely administered orally to the patients without fear of any of the metal’s toxicity consequences.



Metformin tablets, Heavy metals, Permissible daily exposure, Research Subject Categories::PHARMACY