Metformin is a commonly prescribed medication for individuals managing type 2 diabetes. It serves as a foundational treatment to help regulate blood sugar levels. This article aims to provide a clear understanding of Metformin’s interactions with kidney and liver health, addressing frequent questions about its safety and proper usage.
How Metformin Works
Metformin primarily functions by influencing glucose metabolism in several ways. The medication reduces the amount of glucose produced by the liver, a process known as hepatic gluconeogenesis. It also enhances the body’s sensitivity to insulin, allowing peripheral tissues, such as muscles, to absorb and utilize glucose more effectively. Furthermore, Metformin decreases the absorption of glucose from the intestines into the bloodstream. These combined actions contribute to lowering blood sugar levels in individuals with type 2 diabetes.
Metformin and Kidney Function
Metformin is almost entirely eliminated from the body unchanged by the kidneys. When kidney function is impaired, Metformin can accumulate in the body because it is not excreted as quickly. This accumulation, rather than direct damage to healthy kidneys, is the primary concern regarding Metformin and kidney health.
A rare but serious complication linked to Metformin accumulation is lactic acidosis. Lactic acidosis occurs when there is an excessive buildup of lactic acid in the blood, which can be life-threatening if not managed promptly. Symptoms of lactic acidosis can be non-specific but may include abdominal discomfort, decreased appetite, nausea, vomiting, unusual muscle pain or weakness, and unusual sleepiness. Faster or shallow breathing, dizziness, and a general feeling of discomfort are also possible indicators.
Healthcare providers typically use estimated glomerular filtration rate (eGFR) to gauge kidney function. Metformin is generally contraindicated when eGFR falls below 30 mL/min/1.73 m², as this significantly increases the risk of drug accumulation and lactic acidosis. For eGFR levels between 30 and 44 mL/min/1.73 m², starting Metformin is generally not recommended, but if already in use, a reduced daily dose of 1,000 mg or less may be considered with close monitoring. Regular monitoring of kidney function, often annually or more frequently for those with reduced eGFR, helps ensure the continued safe use of Metformin.
Metformin and Liver Function
Metformin primarily exerts its glucose-lowering effects by reducing glucose production in the liver. Despite this direct action on the liver, Metformin is generally not associated with causing liver damage in individuals with healthy liver function. In fact, some research suggests that Metformin may even have beneficial effects on the liver, such as improving outcomes in nonalcoholic fatty liver disease (NAFLD) and potentially reducing the risk of liver cancer in certain patients.
Concerns about Metformin and liver function primarily stem from the rare risk of lactic acidosis, particularly in patients with pre-existing severe liver disease. The liver plays a significant role in clearing lactate from the body, and severe liver impairment can hinder this process, thereby increasing the risk of lactic acid buildup if Metformin were to accumulate. Therefore, while Metformin does not typically cause liver injury, its use is generally avoided or approached with extreme caution in patients with severe liver disease to prevent this potential complication. Routine liver function monitoring is not typically required for Metformin users, unlike the frequent kidney function assessments.
Ensuring Safe Metformin Use
Healthcare providers assess individuals to determine if Metformin is an appropriate treatment. Metformin is contraindicated in those with severe kidney impairment, specifically an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m². It is also avoided in patients with acute or chronic metabolic acidosis, including diabetic ketoacidosis, and in cases of severe liver disease. Other conditions that may increase risk and require caution include acute heart failure, respiratory failure, or any state causing low tissue oxygen levels.
Healthcare providers play a central role by evaluating kidney function with eGFR tests before initiating Metformin and at regular intervals during treatment, typically at least annually. For patients with an eGFR between 30 and 45 mL/min/1.73 m², initiating Metformin is not recommended, and if already prescribed, the dose may be reduced with more frequent monitoring.
There are specific situations where Metformin may need to be temporarily stopped. These include medical procedures involving the use of iodinated contrast dyes, during periods of severe dehydration, or during acute illnesses that could compromise kidney function. For instance, Metformin is often withheld on the day of surgery and for 48 hours afterward, especially if kidney function is reduced or contrast agents are used. Open communication between patients and their healthcare providers about all existing health conditions and medications is important to ensure the safest possible use of Metformin.