Accurate determination of glomerular filtration rate in adults for carboplatin dosing: Moving beyond Cockcroft and Gault

OBJECTIVE

Carboplatin is a cytotoxic chemotherapy drug developed in the 1980s which is still widely used today across various tumour types. Despite its common application, there remains a significant controversy and practice variation on its unique method of dosing by area under the curve (AUC). One potential reason for this variability stems from the reliance of using an estimated glomerular filtration rate (eGFR) as an extrapolation of the measured GFR (mGFR) which the commonly used Calvert equation was originally validated for. This review takes a novel and collaborative nephro-oncology approach to highlight the historical evolution of carboplatin dosing, methods for estimating GFR and its relative performance in the application of carboplatin dosing for adult patients.

DATA SOURCES

We reviewed all pertinent publications comparing carboplatin AUC-based dosing in adult patients based on the various methods of GFR measurements or estimations in order to provide a comprehensive description of each method's advantages and risks.

DATA SUMMARY AND CONCLUSIONS

The Cockcroft-Gault equation has been widely studied but newer eGFR equations, such as the CKD-Epidemiology Collaboration (CKD-EPI) or Janowitz-Williams equation have outperformed the Cockcroft-Gault in recent studies.

Carboplatin dose capping affects pCR rate in HER2-positive breast cancer patients treated with neoadjuvant Docetaxel, Carboplatin, Trastuzumab, Pertuzumab (TCHP)

PURPOSE

Estimated glomerular filtration rate (eGFR) is commonly used to calculate carboplatin doses and capping the eGFR may be used to reduce the risk of excessive dosing and toxicity. We sought to retrospectively examine the impact of our carboplatin guidelines on pathological complete response rates (pCR) and toxicity in women with HER2+ breast cancer receiving neoadjuvant docetaxel, carboplatin, trastuzumab and pertuzumab (TCHP).

METHODS

The delivered area under the curve (dAUC) was calculated [(actual carboplatin dose at cycle 1 ÷ dose calculated with uncapped/unbanded eGFR) × 6] and dichotomized at the median value. The impact of this and other clinical factors on pCR rate, dose intensity (DI) and toxicity was assessed.

RESULTS

124 eligible patients were identified of whom 63.7% (79/124) achieved pCR. The median dAUC at cycle 1 was 5.75 mg × ml/min. Those with lower dAUC were more frequently younger and overweight/obese. Patients with lower dAUC had significantly inferior pCR rates of 54.8% (34/62) vs 72.6% (45/62), respectively (p = 0.040). Similar results were seen in the ER+ subgroup; 45.2% (19/42) vs 68.3% (28/41), p = 0.037%, whereas no significant difference was seen among ER- patients; 75.0% (15/20) vs 81.0% (17/21), p = 0.72. DI and toxicity were comparable between the two dAUC groups.

CONCLUSIONS

The overall pCR rate was high in patients with HER2+ breast cancer receiving the TCHP regimen; however, carboplatin dose capping resulted in inferior pCR rates, particularly in the ER+ subgroup. To ensure optimal dosing, isotopic measurement of renal function is warranted in patients who would otherwise have their eGFR and dose capped.

Analysis of carboplatin dosing in patients with a glomerular filtration rate greater than 125 mL/min: To cap or not to cap? A retrospective analysis and review

The use of the Calvert formula to calculate carboplatin doses allows clinicians to achieve the appropriate carboplatin area under the concentration (AUC) curve. Thrombocytopenia is the dose limiting toxicity of carboplatin and optimizing AUC minimizes the risk of thrombocytopenia. Carboplatin clearance directly correlates with glomerular filtration rate (GFR) and, therefore, an accurate estimation of the renal function is needed. The Calvert formula was designed using the GFR measured by 51Cr-EDTA; however, many clinicians substitute estimated creatinine clearance (CrCl) as calculated by the Cockcroft–Gault (C–G) equation. The potential for overestimating AUC occurs when clinicians substitute actual weight in obese patients or use a low serum creatinine when calculating C–G estimated CrCl. In 2010, the National Cancer Institute recommended the GFR value within the Calvert formula should not exceed 125 mL/min, thereby capping the carboplatin dose. However, there are studies demonstrating that certain patients’ actual GFR values do exceed 125 mL/min. Therefore, capping the carboplatin dose in these patients may lead to underestimating the carboplatin AUC. A single-center, retrospective study was performed to evaluate the change in platelet count pre- and post-carboplatin exposure in patients with C–G estimated CrCl greater than 125 mL/min receiving capped versus uncapped carboplatin doses. A review of carboplatin dosing strategies is also presented. This study indicated there was a larger mean difference in pre- and post-platelet count in patients receiving uncapped carboplatin compared to patients receiving capped carboplatin with no differences in toxicities. Dose capping this patient population will likely lead to a lower AUC rather than the intended AUC target, which could ultimately lead to substandard outcomes.