Metformin Indications, Dosage, Adverse Reactions, and Contraindications

Metformin or dimethyl biguanide is the oral antidiabetic drug with the most extensive experience of prescribing in the clinical practice of type 2 diabetes mellitus. In this chapter, we reviewed the indications, contraindications, and adverse drug reactions (ADR) of metformin. The most significant adverse drug reactions of metformin are lactic acidosis, allergies, hypoglycemia, vitamin B12 deficiency, altered taste, and gastrointestinal intolerance. Metformin is contraindicated in severe chronic diseases (hepatic, renal, and cardiac failure) or acute complications of diabetes (ketoacidosis and hyperosmolar state). Metformin is considered by all international guidelines the first-line treatment in type 2 diabetes mellitus (T2DM) together with medical, nutritional therapy. It is one of the most prescribed molecules worldwide. Furthermore, metformin can also be prescribed for other diseases like polycystic ovary syndrome or prediabetes (impaired glucose tolerance/fasting hyperglycemia). Recent studies have shown positive results concerning the use of metformin for cardiovascular or neuroprotective effects; also, several scientific papers are suggesting an antitumor or antiaging effect of metformin. Having such an excellent efficiency in practice, thus predicting its sustainability on the pharmaceutical market, research is directed toward characterizing metformin action on bacteria genera in the gut. Modifying the microbiota composition by pre- and probiotics could improve metformin action.