Carboplatin AUC From Dose Calculator
Carboplatin AUC From Dose Calculator
The Calvert formula run backwards: what exposure did a given carboplatin dose actually target? Useful for auditing a reduced dose, a flat dose or a dose computed on the wrong kidney function value — which is the commonest reason the answer surprises.
Carboplatin AUC from a given dose
mg and kidney function to AUCDose 600 mg; laboratory eGFR 92 mL/min/1.73 m2; body surface area 1.80 m2; cap applied
The formula rearranged
which is Dose = AUC × (GFR + 25) solved for the exposure
De-indexing, where the GFR is a laboratory eGFR: absolute (mL/min) = indexed (mL/min/1.73 m²) × BSA (m²) ÷ 1.73
- the same two traps
- they run in the opposite direction here. Using an indexed eGFR without de-indexing OVERSTATES the AUC of a given dose in a large patient, because it divides by too small a clearance. And auditing a capped dose against an uncapped kidney function makes it look like an under-dose
- flat dosing
- an analysis of 178 patients and 280 courses put the mean population carboplatin clearance at 8.33 L/h, about 139 mL/min, with about 21% exposure variability from a flat dose. Its authors argued flat dosing is justified in normal renal function, while holding that for a targeted exposure the original formula “remains the method of choice”
- rounding
- carboplatin doses are rounded, so a back-calculated AUC rarely lands on a round number. A 600 mg dose in a patient with an absolute clearance of 95.7 mL/min is an AUC of 4.97, not 5. That is rounding, not an error
- what the exposure does not tell you
- whether it was right. The target belongs to the regimen and the protocol, and the label’s toxicity percentages are cohort figures from its own studies.
Worked example
Dose 600 mg; laboratory eGFR 92 mL/min/1.73 m2; body surface area 1.80 m2; cap applied
De-index: 92 × 1.80 ÷ 1.73 = 95.7 mL/min absolute. Below 125, so the cap changes nothing here
AUC = 600 ÷ (95.7 + 25) = 600 ÷ 120.7 = 4.97 mg/mL per min
So 600 mg was an AUC 5 dose rounded down to a convenient figure, and not a reduction
Skip the de-indexing and the audit goes wrong: 600 ÷ (92 + 25) = 5.13, which overstates the exposure because it divides by too small a clearance
Reverse the question with the fifth line above: the dose that hits AUC 5 exactly on this kidney function is 5 × 120.7 = 604 mg
At the other end of the range, 800 mg on an absolute clearance of 90 mL/min is 800 ÷ 115 = 6.96 — above the labelled single-agent range, where the label's own figures put grade 3 or 4 thrombocytopenia at 33% rather than 16%
The label’s toxicity figures by target AUC, in previously treated patients
| Target AUC | Grade 3 or 4 thrombocytopenia | Grade 3 or 4 leukopenia |
|---|---|---|
| 4 to 5 | 16% | 13% |
| 6 to 7 | 33% | 34% |
Dose to hit a target AUC, by absolute kidney function
| Absolute GFR (mL/min) | AUC 4 (mg) | AUC 5 (mg) | AUC 6 (mg) |
|---|---|---|---|
| 40 | 260 | 325 | 390 |
| 60 | 340 | 425 | 510 |
| 80 | 420 | 525 | 630 |
| 100 | 500 | 625 | 750 |
| 125 (the capped maximum) | 600 | 750 | 900 |
Why you would ever run the formula backwards
A carboplatin dose on a chart is a number of milligrams. The thing that was intended, and the thing the regimen specifies, is an exposure — an area under the concentration-time curve — and the two are related by one line of arithmetic and one kidney function value. Running it backwards answers a question that comes up constantly in practice and in audit: what exposure does this dose actually represent?
There are four common reasons the answer is not the obvious one. The dose may have been rounded, often to a vial-friendly figure, which moves the implied AUC off the round number by a few per cent. It may have been reduced after toxicity, in which case the back-calculated exposure is the size of the reduction, stated in the units the regimen uses. It may have been carried forward from an earlier cycle while the patient’s kidney function changed underneath it — ADDIKD’s position is that recalculation every cycle is unnecessary unless baseline kidney function alters by more than 20% or the clinical picture changes, so a stable dose against a drifting clearance is expected rather than careless. Or it may have been computed on a kidney function value that was wrong.
That last case is why this page carries the same de-indexing and capping machinery as the forward calculation, and the direction the errors run is worth stating precisely. Using an indexed eGFR without de-indexing overstates the exposure of a given dose in a patient larger than 1.73 m², because it divides by too small a clearance — the mirror of the forward error, which under-doses the same patient. And auditing a dose capped at 125 mL/min against an uncapped clearance makes a correct dose look like an under-dose when all that has changed is which convention the auditor used. In a 2.05 m² patient with a reported eGFR of 110, the two conventions and the two indexings span more than 100 mg at a target AUC of 5.
None of this says what the dose should have been. The target AUC belongs to the regimen, and the label’s toxicity percentages are proportions in its own study populations, not risks for an individual. A figure from a cohort is not this patient’s outcome and a response category is not a diagnosis: a stratum in which 42 per cent were alive at fifteen years tells you about that stratum, not which 42 per cent. This page computes a published quantity and states the criteria behind it. It renders no dose, no prescription and no treatment decision — that is the treating team’s. Every coefficient, conversion factor and threshold here is attributed to the source it was read in and, where it is a prognostic figure, to its derivation cohort; where the treating protocol differs, the protocol takes precedence.
Frequently asked questions
How do I work out the AUC from a carboplatin dose?
Divide the dose in milligrams by the GFR in mL/min plus 25. That is the Calvert formula rearranged. The GFR must be an absolute rate in mL/min, so a laboratory eGFR reported per 1.73 m² has to be multiplied by the body surface area and divided by 1.73 first.
Why does my back-calculated AUC come out as 4.97 rather than 5?
Rounding. Carboplatin doses are rounded to a whole number of milligrams, and often further to a vial-friendly figure, so the implied exposure lands a per cent or two off the round number. A 600 mg dose on an absolute clearance of 95.7 mL/min is an AUC of 4.97, which is an AUC 5 dose rounded down.
The dose looks like an under-dose when I audit it. Why?
Three common reasons, all of which this page separates out. The dose may have been computed with the GFR capped at 125 mL/min while you are auditing against an uncapped value. You may be using a de-indexed clearance where the prescriber used the indexed eGFR, or the reverse. Or the kidney function has changed since the dose was set.
Does an AUC above 6 mean the dose was too high?
No. Several regimens, particularly in germ-cell disease and high-dose settings, target above 6 deliberately. The label identifies 4 to 6 for single-agent use in previously treated patients and reports grade 3 or 4 thrombocytopenia in 33% at AUC 6 to 7 against 16% at AUC 4 to 5, but those are cohort proportions and the target belongs to the regimen.
Related calculators
References
- Carboplatin injection, USP: full prescribing information. DailyMed, SPL 5484d2f0-0cc2-4bba-8f26-c7f6539a9606.
- Flat dosing of carboplatin is justified in adult patients with normal renal function. Clin Cancer Res. 2006;12(21):6502–7.
- Cancer Care Ontario. Drug Formulary monograph: CARBOplatin, Section E, dose calculation. Toronto: Ontario Health.
- Tolerability of carboplatin when using rounded serum creatinine values. J Hematol Oncol Pharm. 2012;2(1).
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/