Carboplatin is dosed to a target area under the concentration-time curve rather than to body surface area, because its clearance is almost entirely renal and tracks kidney function closely. The Calvert formula converts a target AUC and the patient’s GFR into a single total milligram dose.
How it works
The core formula is short, but the GFR it uses matters enormously:
dose (mg) = target AUC x (GFR + 25)If a measured GFR is not available, the tool estimates creatinine clearance with Cockcroft-Gault:
CrCl = [(140 - age) x weight(kg) x (0.85 if female)] / (72 x Scr_mg/dL)Creatinine entered in micromoles per litre is converted to mg/dL by dividing by 88.42 before the estimate.
The GFR cap and an example
Because standardised creatinine assays can make estimated GFR read higher than the truth, dosing on an uncapped high estimate risks carboplatin overdose and severe myelosuppression. For that reason the tool caps the GFR used in the formula at 125 mL/min by default. As an example, a target AUC of 5 with a GFR of 90 mL/min gives a dose of 5 x (90 + 25) which is 575 mg total.
Common AUC targets by regimen type
AUC targets vary by protocol, prior treatment, and whether carboplatin is used as a single agent or in combination:
- AUC 5–6 — commonly used in combination regimens (for example with paclitaxel) for gynaecological, lung, or other solid tumours
- AUC 6–7 — used in some single-agent protocols where a higher exposure is sought
- AUC 2 — lower targets are used in some weekly or dose-dense schedules to limit cumulative toxicity
- High-dose (AUC 7–8+) — reserved for certain intensive or stem-cell-supported regimens and requires careful haematological monitoring
The AUC target is always set by the prescribing oncologist based on the protocol and the patient’s prior treatment history, not by this tool. The tool only applies the arithmetic of the Calvert formula once the target is known.
Sources of error in carboplatin dosing
Carboplatin dosing errors are a recognized patient-safety concern, and most arise from a small number of root causes:
Confusing total dose with per-m² dose — AUC dosing gives a total milligram dose for the whole patient, not a dose per square metre of body surface area. Writing a prescription as “575 mg/m²” when you mean “575 mg total” will overdose a patient with a large body surface area by a factor of 1.5–2.0.
Using the wrong GFR input — A recently measured eGFR from the lab may use a different assay or equation than the protocol specifies. Confirm whether the protocol expects a measured GFR (EDTA or iohexol clearance), a Cockcroft-Gault CrCl, or an MDRD or CKD-EPI eGFR before entering the value.
Ignoring renal deterioration between cycles — Carboplatin is nephrotoxic at cumulative doses. Recheck GFR before each cycle and recalculate dose if it has declined; the same AUC target requires a lower dose when the GFR falls.
Always confirm the GFR method, the AUC target, and the final dose against your chemotherapy protocol, and have it independently checked by a pharmacist before it reaches the patient.