Renal Dose Adjustment: Estimating Clearance and What It Means
Estimate creatinine clearance using the Cockcroft-Gault equation — still the reference standard for renal drug dosing — and understand what that figure does and does not tell you about adjusting medication.
The calculator below estimates creatinine clearance, which is a renal function measure — not a dose. It will not tell you how to adjust any specific medication. Dose adjustment thresholds are drug-specific and come from the product label or a pharmacist. Never change a prescribed dose without speaking to your prescriber.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Renal Dose Adjustment: Estimating Clearance and What It Means | — | CrCl = (140 − age) × weight × (0.85 if female) / (72 × Scr) | mL/min |
Step-by-Step Examples
45-year-old man, 80 kg, creatinine 0.9 mg/dL.
- (140 − 45) × 80 = 7600
- 72 × 0.9 = 64.8
- CrCl = 7600 / 64.8 = 117 mL/min
72-year-old woman, 62 kg, creatinine 1.5 mg/dL.
- (140 − 72) × 62 = 4216
- 72 × 1.5 = 108
- CrCl = 4216 / 108 = 39.0
- Female factor: 39.0 × 0.85 = 33.2 mL/min
80-year-old man, 65 kg, creatinine 3.2 mg/dL.
- (140 − 80) × 65 = 3900
- 72 × 3.2 = 230.4
- CrCl = 3900 / 230.4 = 16.9 mL/min
Real-World Applications
Common Mistakes to Avoid
eGFR is indexed to 1.73m² body surface area; Cockcroft-Gault gives an absolute clearance. For a very large or very small patient, the two diverge substantially, and drug labels were written against Cockcroft-Gault.
Cockcroft-Gault assumes steady-state creatinine. When kidney function is changing rapidly, the estimate lags well behind reality.
Knowing clearance is only the first step. Which drugs need adjusting, at what thresholds, and whether by dose reduction or interval extension all come from the specific product information.