Comparison of two formulae for the calculation of glomerular filtration in the dosage of zoledronic acid

Abstract Objective To validate the use of a formula that does not require the patient's weight (Levey formula) for calculating creatinine clearance in the adjustment of the dosage of zoledronic acid. Method Prospective observational study in which zoledronic acid prescriptions in the Oncology and Haematology departments were recorded over the course of 8 months. The adjustment of the dose of zoledronic acid was carried out in accordance with creatinine clearance obtained using 2 different equations; the Cockcroft-Gault equation which is based on medical records, and the Levey formula which does not require the patient's weight for the calculation. The results of zoledronic acid dosage from both equations were compared using the SPSS statistics programme, via the comparison of the 2 measurements using the t Student-Fisher (t test). Results The t test provided a t test value of t = −3.366, with 112 degrees of freedom and a degree of bilateral importance of P = .001. The difference between both measurements was d = −0.051[0.162]) and the confidence interval was 95%, −0.082 to −0.021. From the data obtained in the t test, the degree of bilateral importance (P=.001 Conclusions The difference between the dosages obtained when comparing both methods of glomerular filtration is statistically significant, although not clinically relevant, therefore the MDRD-4 formula (Levey) could be used if the patient's weight is not available.