Impact of Isotope Dilution Mass Spectrometry (IDMS) Standardization on Carboplatin Dose and Adverse Events

When using area under the concentration-time curve-based strategies for dosing carboplatin, accurate estimation of glomerular filtration rate is required for determining dose. Commonly, the Cockcroft-Gault equation is used, which is dependent on measurement of serum creatinine (SCr). Because analysis of SCr changed to an isotope dilution mass spectrometry (IDMS) standard, we sought to determine the impact of this assay change on carboplatin dosing and related toxicity.

This was a single-center, retrospective chart review of adults treated with carboplatin between April 2008 and April 2010 divided into cohorts that initiated carboplatin before or after IDMS standardization. End points included grade 3 thrombocytopenia, decrease in platelet count, and hospitalization and were evaluated in cohorts based on concomitant chemotherapy.

The chart review identified 158 patients, with 63 patients in the pre-IDMS group and 95 patients in the post-IDMS group. Average SCr (pre 1.01 mg/dl vs post 0.86 mg/dl, p<0.001) and average carboplatin dose (pre 580 mg vs post 703 mg, p<0.001) were significantly different between the groups. The frequency of grade 3 thrombocytopenia was not statistically significant across three partner chemotherapy cohorts before and after IDMS implementation.

IDMS standardization led to an overall decrease in SCr with subsequent increase in carboplatin doses. However, no increase in recorded adverse events was observed, suggesting that the clinical relevance in toxicity from higher doses was minimal.