Metformin is a widely prescribed medication for individuals managing type 2 diabetes. For those taking metformin, understanding its relationship with kidney health is important for safe and continued use.
Metformin and Its Connection to Kidney Health
Metformin belongs to a class of drugs known as biguanides, working primarily by reducing the amount of glucose produced by the liver. It also helps the body respond better to insulin, which aids in the uptake of sugar from the blood. This combined action helps to lower blood glucose levels in people with type 2 diabetes.
The kidneys are responsible for filtering waste products from the blood and excreting them in urine. Metformin is not metabolized by the body; instead, it is almost entirely eliminated from the body unchanged by the kidneys. Therefore, healthy kidney function is important to ensure the medication is cleared efficiently. If kidney function declines, metformin can build up in the bloodstream, leading to potential complications.
To assess kidney function, healthcare providers often measure creatinine levels in the blood. Creatinine is a waste product generated from normal muscle breakdown and dietary protein digestion. An elevated creatinine level can indicate that the kidneys are not filtering as well as they should be.
While creatinine provides an indication, the estimated Glomerular Filtration Rate (eGFR) is a more comprehensive measure of kidney function. The eGFR is calculated using a formula that considers creatinine levels along with other factors such as age, sex, and sometimes race. This calculation provides an estimate of how much blood the kidneys filter per minute. Regular monitoring of eGFR is typically part of routine care for individuals taking metformin.
Key Kidney Function Thresholds for Metformin
Healthcare providers rely on eGFR values to make informed decisions about metformin dosage and whether to continue its use. General guidelines, including those from the U.S. Food and Drug Administration (FDA), provide specific thresholds for kidney function.
Metformin is generally not recommended for individuals with an eGFR below 30 mL/min/1.73m², as this indicates severe kidney impairment. In such cases, metformin is considered contraindicated. Continuing metformin with an eGFR below this level significantly increases the risk of drug accumulation. If a patient’s eGFR falls below 30 mL/min/1.73m² while on metformin, the medication should be discontinued.
For patients with an eGFR between 30 and 45 mL/min/1.73m², caution is advised. Starting metformin in this range is typically not recommended. If a patient is already taking metformin and their eGFR falls into this range, healthcare providers assess the benefits and risks of continuing treatment. Dosage adjustments, often a reduction, and more frequent kidney function monitoring may be necessary.
Understanding the Risks of Impaired Kidney Function with Metformin
The thresholds for kidney function are important due to the risk of metformin accumulation, which can lead to a serious but rare condition called lactic acidosis. While rare, it can be a severe complication with potentially serious outcomes.
Metformin accumulation, resulting from impaired kidney clearance, can disrupt the body’s metabolic processes, leading to increased lactate production and reduced lactate clearance. This imbalance contributes to the development of lactic acidosis.
Symptoms of lactic acidosis can be subtle initially but may include unusual muscle pain or weakness, trouble breathing, and stomach discomfort. Other indicators might involve unusual sleepiness, dizziness, or feeling cold, especially in the extremities. Recognizing these signs and seeking immediate medical attention is important if they occur while taking metformin.
Living with Metformin and Maintaining Kidney Health
Regular monitoring of kidney function is a standard practice for individuals taking metformin. This typically involves periodic blood tests to measure creatinine levels and calculate eGFR, ensuring that the kidneys are functioning adequately. The frequency of these tests may increase for individuals at higher risk of developing kidney impairment, such as older adults.
Maintaining open communication with healthcare providers is important. Patients should report any changes in their health, new symptoms, or the use of other medications to their doctor. This information helps healthcare professionals assess potential interactions or changes in kidney function that could affect metformin use. Prompt reporting allows for timely adjustments to treatment plans.
There are specific situations where metformin might need to be temporarily stopped, even if kidney function is generally stable. For instance, before certain medical procedures involving iodinated contrast dye, such as CT scans, or prior to surgery, doctors may advise temporarily discontinuing metformin. This precaution is taken because these procedures can temporarily affect kidney function, which could increase the risk of metformin accumulation.
It is important to never self-adjust or stop metformin without consulting a healthcare provider. Discontinuing the medication without medical guidance can lead to uncontrolled blood sugar levels. If metformin needs to be permanently discontinued due to kidney function changes, healthcare providers can discuss and transition to alternative diabetes treatments.