Aims Drug prescription is difficult to manage in patients with chronic kidney disease (CKD). We assessed the prevalence and determinants of inappropriate drug prescriptions (whether contraindications or inappropriately high doses) with regard to kidney function in patients with CKD under nephrology care. We also assessed the impact of the equation used to estimate GFR on the prevalence estimates. Methods Results The CKD-REIN cohort includes 3033 outpatients with CKD (eGFR between 15 and 60 ml min(-1) 1.73 m(-2)). We examined the daily doses of pharmacological agents prescribed at study entry. Inappropriate prescription was defined as the reported prescription of either a contraindicated drug or an indicated drug at an inappropriately high dose level with regard to the patient's GFR, as estimated with the CKD-EPI equation, the de-indexed CKD-EPI equation, or the Cockcroft-Gault (CG) equation. Multivariate logistic regression was used to assess the determinants of inappropriate prescription risk. At baseline, patients' median [interquartile range] number of drugs prescribed per patient was 8 [5-10]. Half of the patients had been prescribed at least one inappropriate drug. Anti-gout, cardiovascular agents and antidiabetic agents accounted for most of the inappropriate prescriptions. The percentage of inappropriate prescriptions varied from one GFR equation to another: 52% when using the CKD-EPI equation, 47% when using the de-indexed CKD-EPI equation and 41% with the CG equation. A multiple logistic regression analysis showed significantly higher odds ratios [95% confidence interval] for inappropriate prescriptions in male patients (1.28 [1.07; 1.53]), patients with diabetes (1.34 [1.06; 1.70]), those with a high BMI (1.58 [1.25; 1.99]), and those with a low GFR (10.2 [6.02; 17.3]). The risk of having at least one inappropriate prescription increased with the number of drugs per patient (P for trend \textless 0.0001) and therefore the odds ratio was 5.88 [4.17; 8.28] for those who received at least 11 prescribed medications compared to those who received fewer than 5. Conclusion Appendix Our results emphasize the complexity of drug management for CKD patients, for whom inappropriate prescription appears to be common.