Every week, we shall write about a drug that we commonly use to manage diseases to help us understand it better. And this week’s drug is metformin. Metformin is the first-choice drug when treating type 2 diabetes mellitus. We either use it alone or in combination with other oral hypoglycaemic drugs or insulin. A key feature of metformin is that it doesn’t cause hypoglycaemia.
Metformin is a biguanide. It decreases blood glucose levels by increasing the body’s sensitivity to insulin. It also halts the synthesis of glucose in the liver. It enables efficient glucose uptake and utilisation by the skeletal muscles. It also suppresses the absorption of glucose by the intestines. Important to note, metformin doesn’t stimulate insulin secretion from the pancreas. It does not, therefore, cause hypoglycaemia. The drug halts weight gain and can induce weight loss.
Weight reduction is key to the long-term management of diabetes. It’s key to preventing insulin resistance.
Its side effects are mostly related to intestinal glucose suppression. They include nausea, vomiting, anorexia, taste alteration, and diarrhoea. A fatal but rare adverse effect is lactic acidosis.
Lactic acidosis never occurs in stable patients. However, some conditions can precipitate the condition when either cause metformin accumulation, increase lactate production, or reduced lactate breakdown. It may be due to kidney failure, sepsis, or liver failure, respectively.
It’s noteworthy that the kidneys excrete metformin unchanged. Patients with kidney impairment require a dose adjustment.
We don’t prescribe it to those with end-stage renal disease. We temporarily withhold metformin in acute kidney injury, cardiac or respiratory failure. We take caution in patients with impaired liver function because this may slow down lactate metabolism. We also withhold it in acute alcohol intoxication or chronic alcohol overuse. The former may precipitate lactic acidosis, whereas the latter increases the risk of hypoglycaemia.
When a patient goes for any radiological intervention involving contrast media, we withhold metformin before and 48 hours after injection. Contrast media may increase the risk of renal impairment, drug accumulation and lactic acidosis.
We cautiously combine metformin with drugs that can impair kidney function. They include nonsteroidal inflammatory drugs (NSAIDs) like ibuprofen, angiotensin-converting enzyme inhibitors like captopril.
A few drugs like prednisolone, thiazide and loop diuretics increase blood glucose levels. They, therefore, oppose the actions and decrease the efficacy of metformin.
Metformin is a long-term treatment. We only stop or change it if intolerable side effects arise or the drug becomes contraindicated. Read more about it from here.