From Synthalin to Metformin:is a Century Cycle of Biguanides as Oral Antidiabetic drugs Now Closed?

After the first release of synthalin B (dodecamethylenbiguanide) in 1928 and its later retraction in the 1940s in Germany and the retraction of phenformin (N-Phenethylbiguanide) because of the letal complication of acidosiss,metformin (1-1-dimethylbiguanide) was first released in France in 1959 and then in the USA in 1995 for oral treatment of diabetes type 2. Acute gastrointestinal side effects often lead to dose reduction and strongly limit adherence to therapy.Main long-term consequences are deficency of vitamin B12 and of iron and sometimes also acidosis development. Intravenously injected F18-labelled glucose in metformin-treated type 2 diabetics accumulates in the the small and even more in the large intestine.The densitometry picture observed in metformin-treated diabetics is similar to that observed in patients after bowel-cleansing or chronically taking different types of laxatives where the accumulated radioactivity can even reach values observed in colon cancer. The glucose-lowering mechanism of action of metformin is therefore not only due to inhibition of glucose uptake in the small intestine but also to „attraction“ of glucose from the hepatocyte to the intestine,possibly through its secretion into the bile.Metformin is not different from the other biguanides ,synthalin B and phenformin.The mechanism of action,and the side effects are comparable to those of laxatives.