Research Article Vol: 2; Issue: 3 Study of Antimicrobial and Antioxidant potentiality of Anti-diabetic drug Metformin. Fatema Nasrin 1* 1 Department of Pharmacy, Southeast University, Banani, Dhaka-1213, Bangladesh. Date Received: 21-Feb-2014 Date of Accepted: 18-Mar-2014 Date Published: 21-Mar-2014 220 Abstract: Metformin, an oral hypoglycemic drug was studied in vitro for possible antibacterial and antioxidant activity. Antimicrobial activity of metformin was evaluated against 9 Gram-positive, Gram-negative bacteria and 3 fungi using disk diffusion technique. Kanamycin (30µg/disc) was used as standard. Antioxidant potentiality of metformin was investigated by DPPH scavenging activity. Metformin active at 500 µg/ml, showed very good antimicrobial activity against most of the bacterial strains with an average zone of inhibition of 12-15mm. Metformin demonstrated a pronounced inhibitory action against Pseudomonas aeruginosa, an organism which is known to be multidrug resistant. The tested fungi are Saccharromyces cerevaceae, Candida albicans and Aspergillus niger. The tested drug showed very good antifungal activity with an average 13 -17 mm zone of inhibition. The percentage (%) scavenging of DPPH free radical of metformin was found to be concentration dependent with IC 50 value 56.90± 0.83μg µg/ml while IC 50 value of standard ascorbic acid was found to be 51.89 ± 1.11µg/ml. The results of these studies indicated that metformin could be significantly protect animals from tested pathogenic bacteria as well as might be beneficial for diabetic patient more than a hypoglycemic drug. Keywords: Metformin, Antimicrobial activity, zone of inhibition, antioxidant, free radical. Introduction Anti-microbial drug resistance is a serious global health issue compromising the treatment of bacterial, viral, fungal and parasitic infections (1). New drugs or new drug combinations may be the solution in the battle against resistance development in serious infectious diseases. The concept of reversal of resistance by means of non-antibiotics may be a solution for bringing drug resistant micro-organisms back to their original sensitivity to the classical antibiotics (2). A variety of compounds which are employed in the management of pathological conditions of a non-infectious aetiology have also been shown to modify cell permeability and to exhibit broad-spectrum antimicrobial activity in vitro against bacteria and other microorganisms(3,4,5).There is evidence that certain nonantibiotic compounds, alone or in combination with conventional antibiotics, may play a useful role in the management of specific bacterial infections associated with high risk of resistance to conventional antibiotics (6,7, 8). Drugs belonging to different pharmacological classes such as Antihistamines(Diphenhydramine,Bromodiphenhydramine 9, Promethazine 10), Psychotropics (Promazine 11, chlorpromazine 12, Fluphenazine, Trifluoperazine), Antihypertensive (Methyl-DOPA 13), Local anesthetics (procaine), Hypoglycemic possess powerful antibacterial activity. Such chemotherapeutic agents have been grouped together and are now entitled as “Non- antibiotics” 14,4. The present paper describes the antimicrobial and antioxidant potentiality of a hypoglycemic drug, metformin. Metformin (Figure 1) is an oral antidiabetic drug in the biguanide class. It is the first-line drug of choice for the treatment of type 2 diabetes, in particular, in overweight and obese people and those with normal kidney function. Its use in gestational diabetes has been limited by safety concerns. It is also used in the treatment of polycystic ovary syndrome, and has been investigated for other diseases where insulin resistance may be an important factor. Metformin works by suppressing glucose