How this instrument works
Carboplatin, a platinum chemotherapy drug, is unusual in that its dose is calculated from a patient's kidney function rather than from body surface area the way most chemotherapy is dosed. Calvert and colleagues published the formula behind this practice in 1989, after finding that carboplatin's clearance from the body tracked glomerular filtration rate (GFR) closely enough to predict the dose needed to hit a chosen target AUC — area under the concentration-time curve, a measure of total drug exposure over the course of treatment.
The formula itself is simple: dose in milligrams equals the target AUC multiplied by GFR plus 25, a small constant standing in for drug clearance pathways beyond the kidneys. Everything this page calculates depends on two numbers supplied from outside it — the target AUC, which the treating oncologist selects based on the specific regimen, the drug combination, and the patient's treatment history, and the GFR, which comes from a separate kidney-function test or estimate. This page performs only the multiplication; it makes neither clinical decision.
This page also caps the GFR value at 125 mL/min before applying the formula, and that cap has its own separate history worth stating plainly: it was not part of Calvert's original 1989 paper. The cap was added later, in 2010, when the National Cancer Institute recommended it after laboratories switched to newer, isotope-dilution-mass-spectrometry-traceable methods for measuring serum creatinine. Those newer assays tend to read serum creatinine somewhat lower than older methods, which pushes calculated GFR higher, and left uncapped, that shift can inflate the Calvert-formula dose in a way that raises toxicity risk without a matching gain in effect. Capping GFR at 125 mL/min was the safety measure introduced to prevent that inflation.
Because this page performs arithmetic on numbers chosen elsewhere, its output is only as sound as the AUC and GFR fed into it. Neither figure is something a calculator should select: the target AUC reflects a treatment protocol and clinical judgment specific to one patient, and GFR itself is normally estimated or measured by methods carrying their own margins of error. The number produced here is a starting point for a pharmacist or oncologist to review, not a dose to act on unassisted.
- Enter Target AUC (mg/mL·min), the drug-exposure target set by the treating oncologist for this specific regimen.
- Enter GFR (mL/min), the patient's glomerular filtration rate from a kidney-function test or estimate.
- Read Carboplatin dose (mg) — target AUC multiplied by GFR, capped at 125 mL/min, plus 25.
- Treat the result as an arithmetic starting point for pharmacist and oncologist review, never a dose to administer directly from this page.
Worked example — three Calvert formula doses
A target AUC of 5 with a GFR of 90 mL/min, below the 125 cap: dose = 5 × (90 + 25) = 5 × 115 = 575 mg. Since 90 is already under the cap, the cap has no effect here, and the formula runs exactly as Calvert's 1989 paper describes it.
The same target AUC of 5 with a GFR of 150 mL/min, above the cap: the calculation substitutes 125 for 150, giving dose = 5 × (125 + 25) = 5 × 150 = 750 mg. Without the cap, the uncapped GFR of 150 would give dose = 5 × (150 + 25) = 5 × 175 = 875 mg — a 125 mg difference, large enough to matter clinically, and exactly the inflation the 2010 cap exists to prevent.
A higher target AUC of 6 with a reduced GFR of 60 mL/min: dose = 6 × (60 + 25) = 6 × 85 = 510 mg. A lower GFR pulls the dose down, because impaired kidney clearance means the same milligram amount stays in the body longer, so less drug is needed to reach the same exposure target.
Questions
Who decides the target AUC used in this calculation?
The treating oncologist, based on the specific chemotherapy regimen, the drugs carboplatin is combined with, and the patient's treatment history — never this page. This calculator only multiplies the AUC value it's given by the GFR term; choosing what that AUC should be is a clinical decision made entirely outside any calculator.
Why does carboplatin dosing depend on kidney function instead of body size?
Because Calvert and colleagues found in 1989 that carboplatin clearance from the body correlates closely with glomerular filtration rate — closely enough that a formula built on GFR alone predicted the dose needed to hit a target drug exposure more reliably than the body-surface-area dosing used for most other chemotherapy.
Where does the 125 mL/min GFR cap come from?
It's a 2010 addition from the National Cancer Institute, not part of Calvert's original 1989 formula. It responds to a change in how laboratories measure serum creatinine: newer IDMS-traceable assays tend to report serum creatinine lower than older methods, which pushes calculated GFR higher and can inflate the Calvert-formula dose without a real gain in effect. Capping GFR at 125 mL/min before the multiplication keeps that assay change from silently increasing doses.
How much difference does the GFR cap actually make?
It depends on how far over 125 mL/min the raw GFR sits, but the gap can be clinically meaningful — at a target AUC of 5, a GFR of 150 mL/min gives 750 mg with the cap applied versus 875 mg without it, a 125 mg difference. That is the scale of inflation the cap was introduced specifically to prevent.
Is the number this calculator produces the dose I should receive?
No. It is the result of one formula applied to two numbers you supplied, not a prescribing decision. The actual dose a patient receives also depends on which GFR-estimating method was used, rounding conventions, dose-capping policies at a given institution, and the oncologist's and pharmacist's review, all of which sit outside what this page calculates.
What is AUC in the context of this formula?
Area under the concentration-time curve — a measure of the total drug exposure a patient receives over the course of treatment, rather than a peak concentration or a fixed milligram amount. Target AUC values for carboplatin regimens are typically set within a range such as 4 to 6, chosen by the treating oncologist to match the specific protocol being followed.
References
- Calvert AH et al. 1989, J Clin Oncol — Calvert formula (PubMed)
- Carboplatin dosing and IDMS-creatinine GFR capping (PMC)
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.