This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
The Calvert formula
Carboplatin is cleared almost entirely by the kidneys, so its exposure depends on kidney function more than on body size. Instead of dosing by body surface area, oncologists aim for a target area under the curve (AUC) of drug concentration over time, using the formula published by Hilary Calvert and colleagues in 1989:
Dose (mg) = target AUC (mg/mL·min) × (GFR + 25)
The 25 mL/min stands for the part of the drug cleared by routes other than the kidneys. The target AUC comes from the treatment protocol, often between 4 and 7 depending on the regimen and on earlier treatment.
Estimating the GFR
The glomerular filtration rate (GFR) can be measured, for example with a radioisotope test, or estimated. The calculator uses the Cockcroft-Gault creatinine clearance:
CrCl = (140 − age) × weight (kg) ÷ (72 × creatinine in mg/dL), multiplied by 0.85 for women.
The 125 mL/min cap
Since modern laboratories standardized creatinine assays, low creatinine values can lead to an overestimated GFR and an overdose. The US Food and Drug Administration advised capping the GFR at 125 mL/min, so the maximum dose is 150 × AUC:
| Target AUC | Maximum dose |
|---|---|
| 4 | 600 mg |
| 5 | 750 mg |
| 6 | 900 mg |
Example
A 60-year-old man weighing 70 kg with a creatinine of 1.0 mg/dL has a Cockcroft-Gault clearance of about 78 mL/min. For an AUC of 5, the dose is 5 × (78 + 25), about 515 mg.
Points to check
- Protocols differ on which weight to use in obesity (actual, ideal or adjusted) and on whether to set a minimum creatinine value, for example 0.7 mg/dL.
- Some centers use a measured GFR or a CKD-EPI estimate not adjusted for body surface area.
- Very low or unstable kidney function makes any estimate unreliable.
The final dose must always be checked against the protocol and by the oncology pharmacist.