Many renally cleared drugs are dosed from creatinine clearance estimated with the Cockcroft-Gault equation, which includes body weight. In patients with obesity, actual body weight overestimates clearance and can lead to overdosing; ideal body weight can underestimate it.
Common practice is to use ideal body weight when actual weight is close to it, and an adjusted body weight in obesity. Low muscle mass in frail older adults also inflates the estimate, because serum creatinine is low for reasons unrelated to kidney function.
- Record height and weight before calculating creatinine clearance.
- Use adjusted body weight in patients with obesity, following local protocol.
- Be cautious with low creatinine values in frail or immobile patients.
- Follow the drug label's specified method when it names one.
Why it matters
Renal dose errors often come from the input, not the formula.
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