From the Guidelines
The estimated creatinine clearance for a 98-year-old patient weighing 47.7 kg with a serum creatinine of 0.86 mg/dL is approximately 25-30 mL/min, indicating moderate renal impairment, as calculated using the Cockcroft-Gault formula 1. This calculation is likely based on the Cockcroft-Gault formula, which accounts for age, weight, serum creatinine, and gender (though gender wasn't specified in the question). Some key points to consider:
- With this level of renal function, medication dosing adjustments are necessary for many drugs that are primarily eliminated by the kidneys.
- Common medications requiring dose reduction include certain antibiotics (like fluoroquinolones), gabapentinoids, direct oral anticoagulants, and many antidiabetic medications.
- The patient should avoid nephrotoxic medications when possible, maintain adequate hydration, and have renal function monitored regularly.
- This level of renal impairment is not unusual for advanced age, as kidney function typically declines approximately 1 mL/min per year after age 40, as noted in the National Kidney Foundation practice guidelines 1.
- The patient's healthcare provider should consider this creatinine clearance when prescribing medications and monitoring for adverse effects.
From the Research
Calculating Creatinine Clearance
To calculate creatinine clearance, we can use the Cockcroft-Gault equation, which takes into account the patient's weight, age, and serum creatinine level.
- The formula for calculating creatinine clearance is:
- CrCl (male) = ((140 - age) * weight in kg) / (72 * serum creatinine)
- CrCl (female) = ((140 - age) * weight in kg) / (72 * serum creatinine) * 0.85
- Given the patient's weight (47.7 kg), age (98 years), and serum creatinine (0.86 mg/dL), we can calculate the creatinine clearance as follows:
- CrCl (female) = ((140 - 98) * 47.7) / (72 * 0.86) * 0.85
Results
- Calculating the creatinine clearance using the given values, we get:
- CrCl = ((42) * 47.7) / (72 * 0.86) * 0.85
- CrCl = (2001.4) / (61.92) * 0.85
- CrCl = 32.29 * 0.85
- CrCl = 27.45 mL/min
Clinical Implications
- According to the studies 2, 3, 4, 5, 6, metformin can be safely used in patients with mild to moderate renal impairment, but its use in severe renal impairment is still a topic of debate.
- The calculated creatinine clearance of 27.45 mL/min falls below the recommended threshold for metformin use, suggesting that the patient may be at risk for lactic acidosis.
- However, as noted in the studies 2, 4, 5, the risk of lactic acidosis associated with metformin use in patients with impaired kidney function may be lower than previously thought, and the benefits of metformin therapy may outweigh the risks in some cases.
- Therefore, the decision to use metformin in this patient should be made on a case-by-case basis, taking into account the patient's individual risk factors and medical history, as well as the potential benefits and risks of therapy, as discussed in the studies 2, 3, 4, 5, 6.