Metformin is widely used to manage blood sugar in type 2 diabetes. It is also prescribed to prevent type 2 diabetes in high-risk individuals and for gestational diabetes. The medication plays a role in helping the body process insulin more effectively, which is crucial for maintaining balanced blood glucose. Understanding the appropriate dosage of metformin is important for its safe and effective use.
Understanding Metformin’s Role
Metformin works to lower elevated blood sugar through several key actions within the body. A primary mechanism involves reducing the amount of glucose produced by the liver. The medication also helps improve how the body’s muscle cells respond to insulin, allowing them to absorb glucose more efficiently from the bloodstream. Additionally, metformin decreases the amount of glucose absorbed from food in the intestines. These combined effects contribute to better overall blood sugar control.
Typical Metformin Dosages and Daily Limits
The dosage of metformin prescribed varies significantly among individuals, beginning with a low dose and gradually increasing to minimize side effects. This process of slow increase, known as titration, allows the body to adjust to the medication. Metformin is available in both immediate-release (IR) and extended-release (ER) formulations, each with distinct dosing schedules.
For immediate-release metformin, adults typically start with 500 milligrams (mg) twice daily or 850 mg once daily, taken with meals. The dose is then usually increased in increments of 500 mg weekly or 850 mg every two weeks, based on how well blood sugar is controlled and how the medication is tolerated. The usual maintenance dose ranges from 1500 mg to 2550 mg per day, divided into two or three doses. The maximum daily dose for immediate-release metformin is 2550 mg.
Extended-release metformin is typically started at 500 mg to 1000 mg once daily, usually with the evening meal. Dosage increases are often made in 500 mg increments weekly. The maximum daily dose for most extended-release formulations is 2000 mg. It is important to swallow extended-release tablets whole and not to crush or chew them.
Factors Influencing Your Prescribed Dose
A healthcare provider determines the appropriate metformin dosage based on various individual health factors. Kidney function is a primary consideration, as metformin is primarily eliminated through the kidneys. Metformin is generally not recommended to be started if the estimated glomerular filtration rate (eGFR) is between 30 and 45 mL/min/1.73 m², and it is contraindicated if the eGFR falls below 30 mL/min/1.73 m². For patients already taking metformin, the dose may need to be reduced if the eGFR drops below 45 mL/min/1.73 m², and the medication should be discontinued if it falls below 30 mL/min/1.73 m².
Liver function also plays a role, as metformin should generally be avoided in individuals with hepatic impairment due to an increased risk of a serious side effect called lactic acidosis. Age is another factor; older adults may require a lower initial and maintenance dose because they are more likely to have reduced kidney function. Individual response to the medication and the presence of other medical conditions or medications can also necessitate dosage adjustments.
Side Effects and Safety Precautions
Metformin can cause side effects, with gastrointestinal issues being the most common, especially when treatment begins. These often include nausea, vomiting, diarrhea, stomach ache, bloating, gas, and a metallic taste in the mouth. Taking metformin with meals and gradually increasing the dose can help mitigate these symptoms. Extended-release formulations may also offer improved gastrointestinal tolerability for some individuals.
A rare but severe side effect of metformin is lactic acidosis, a condition where lactic acid builds up in the blood. Symptoms of lactic acidosis can include extreme tiredness, weakness, muscle pain, difficulty breathing, stomach discomfort, dizziness, lightheadedness, a cold feeling, and a fast or slow heart rate. Immediate medical attention is necessary if these symptoms occur. Risk factors for lactic acidosis include kidney or liver impairment, excessive alcohol consumption, and certain medical procedures.
Long-term use of metformin can sometimes lead to vitamin B12 deficiency. Healthcare providers may monitor B12 levels, especially in patients on higher doses or prolonged therapy. It is also important to temporarily stop metformin before certain medical procedures, particularly those involving intravenous contrast dye, like some CT scans. The medication is typically withheld for 48 hours before the procedure and for 48 hours afterward, only being restarted once kidney function is confirmed to be stable. Alcohol consumption should be limited or avoided while taking metformin, as it can increase the risk of lactic acidosis and hypoglycemia (low blood sugar).