[Clarification of the method used for drug dosage adjustment in patients with renal failure: The CLEAR study].

Introduction: The French National Authority for health recommends that the adjustment of the dosage of drugs in patients with renal insufficiency be carried out on the basis of an estimate of renal function using the Cockcroft-Gault formula, while the estimation of the glomerular filtration rate using the Modification of Diet in Renal Disease or CKD-EPI formula is recommended for the diagnosis and monitoring of renal insufficiency. The argument put forward is that the recommendations for dosage adjustment of the summaries of product characteristics would have been established on the basis of the use of this formula. Service ICAR aimed at verifying the evidence supporting this argument.

Methods: In all, 2447 summaries of product characteristics were analyzed to identify the renal function criterion specified for dose adjustment recommendations. When no formulas were found in the summary of product characteristics, the firms were contacted to obtain information on renal function estimation methods used in developmental studies. Their responses were analyzed.

Results: Of the 2447 summaries of product characteristics studied, 438 (17.9%) propose a dosage adjustment in case of renal insufficiency. No formula is mentioned in the summarie of product characteristics for 90.0% of them. The Cockcroft-Gault and Modification of Diet in Renal Disease/CKD-EPI formulas are found in 8.7% and 0.7% respectively of these 438 summaries of product characteristics. After contacting pharmaceutical companies and analysis of the data available in the studies on which the summaries of product characteristics were based, the information cannot be found for 63.0% of the summaries of product characteristics, in spite they mention the need to adjust the dosage in case of renal insufficiency.

Conclusion: The majority of summaries of product characteristics do not mention the Cockcroft-Gault formula and in the majority of cases it is not possible to identify the formula or technique used in the studies on which is based the reference to dosage adjustment in the summarie of product characteristics. In addition, there are discrepancies between the wording of the summaries of product characteristics and the data from development studies. The use of Cockcroft-Gault for dosage adjustment is to be questioned, especially since the Isotope-dilution mass spectrometry, or IDMS, standardization of creatinine dosage makes obsolete studies based on Cockcroft-Gault formula and a non-standardized dosage, and thus the use of Cockcroft-Gault not transposable to current clinical practice.