From the Research
For a 79-year-old female with a GFR of 55, metformin can be prescribed at a starting dose of 500 mg once or twice daily, with a maximum recommended dose of 1,000 mg twice daily. Given her age and moderately reduced kidney function, it's prudent to start at the lower end of the dosing range (500 mg once daily) and titrate up gradually based on glycemic response and tolerability. Her GFR of 55 ml/min indicates Stage 3a chronic kidney disease, which allows for metformin use but requires dose adjustment and careful monitoring. Regular kidney function assessment every 3-6 months is essential as metformin is primarily eliminated by the kidneys, and declining renal function increases the risk of lactic acidosis. Common side effects to monitor include gastrointestinal symptoms like nausea, diarrhea, and abdominal discomfort, which can be minimized by taking the medication with meals and slowly increasing the dose. If her GFR drops below 30 ml/min, metformin would be contraindicated due to increased risk of lactic acidosis.
Some key points to consider when prescribing metformin in this patient include:
- Monitoring for signs of lactic acidosis, such as muscle pain, weakness, or respiratory distress, especially if her kidney function declines 1
- Adjusting the dose based on her kidney function and glycemic response, with a maximum recommended dose of 1,000 mg twice daily 2
- Considering alternative treatments if her GFR drops below 30 ml/min or if she experiences significant side effects 3
- Regularly assessing her kidney function and adjusting her treatment plan as needed to minimize the risk of adverse events 4
It's also important to note that the evidence suggests that metformin can be safely used in patients with moderate kidney impairment, but careful monitoring and dose adjustment are necessary to minimize the risk of lactic acidosis 5. Overall, the key is to balance the benefits of metformin in managing her diabetes with the potential risks and to closely monitor her kidney function and overall health.