Very high GFR in cancer patients undergoing chemotherapy: prevalence, carboplatin dosing patterns and chemotherapy toxicity

Aim: Carboplatin dosing depends on accurate glomerular filtration rate (GFR) estimation. There is a lack of clinical agreement about carboplatin dosing when the GFR measurement is very high (>110mL/min). Methods: A retrospective audit of pre-chemotherapy 99m technetium (Tc) diethylenetriamene pentaacetate (DTPA) radionuclide GFR estimations and patients' chart review were performed from January 2006 to May 2009. The primary objective was to determine the prevalence of patients with a high GFR and the incidence of myelotoxicity in this group. Results: Overall 18 of 148 treated patients (14%) measured GFR >110mL/min. The GFR values of six of the 18 patients were capped for dose calculation. In eight patients a measured GFR corrected for body surface area was used and in four the actual measured GFR was used for dose calculation. In total, 63 cycles of chemotherapy were delivered. Grade III or IV myelotoxicity accounted for 37% (15/41) of all myelotoxicities. Neutropenia accounted for almost 39% of all myelotoxicities (16/41). Two patients (11%) were hospitalized due to febrile neutropenia. Eight patients (40%) had dose reduction and four (20%) had treatment delays due to myelotoxicity. The frequency of myelotoxicity was high irrespective of the GFR used (corrected or uncorrected) in calculating the chemotherapy dose. Conclusion: High values of GFR, by 99mTc DTPA radionuclide measurement, are a common finding in pre-chemotherapy patients irrespective of age. Carboplatin dosing patterns in this group of patients vary among treating oncologists and a standardized approach is needed.