Metformin (1,1-dimethylbiguanide) is an anti-hyperglycemic agent that is commonly used in the oral treatment of Type 2 Diabetes Mellitus. Phenformin (phenethylbiguanide) is its structural analog. As an anti-hyperglycemic agent, metformin is known to affect glucose transporters. Lactobacillus acidophilus is a bacteria that ferments lactic acid under anaerobic conditions and is known to contain numerous glucose transporters. Inconclusive results were seen during NMR analysis due to the lack of lactic acid and the increase of glucose over time. With completely anaerobic conditions and longer measurement periods, it is hopeful that further experimentation will be successful. Adenosine deaminase is involved in purine nucleoside metabolism. Based on molecular docking simulations, we have hypothesized that adenosine deaminase could be inhibited by metformin and phenformin, and that phenformin is a better inhibitor than metformin. The inhibitory effect of metformin and phenformin on adenosine deaminase from bovine spleen was studied spectrophotometrically. Non-linear regression analysis was used to obtain the inhibition constants. Metformin was a competitive inhibitor of deamination of adenosine with the inhibition constant, KI, of 88 mM. Phenformin was slightly more effective than metformin as a competitive inhibitor with KI of 10 mM. The KM of adenosine was 31 μM. The inhibition constant values indicate that neither metformin nor phenformin is a potent inhibitor of adenosine deaminase. It is unlikely that at the physiological concentration, adenosine deaminase activity would be greatly affected by either drug.