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Objectives: The prevalence of kidney disease (KD) indicators together with the profile of RA drugs prescribed in RA patients was investigated in the MATRIX study (MeThotreXate And Renal Insufficiency)., Methods: Renal function (RF) was assessed using Cockcroft-Gault (CG) and abbreviated Modification of Diet in Renal Disease (aMDRD) study formulae., Results: Serum creatinine (SCr) was normal in 81.4% of the 129 patients included. According to the National Kidney Foundation (NKF) classification, the distribution by stage of KD was, using the aMDRD and CG formulae, as follows: stage 1: 11.3% and 11.4%; stage 2: 20.0% and 20.3%; stage 3: 15.0% and 24.1%; stage 4: 0% and 1.3%; stage 5: 0%. Proteinuria, haematuria and leucocyturia were observed in 16%, 17% and 20% of the patients, respectively. Using the aMDRD and CG formulae, 36% and 38% of the prescriptions made in patients with glomerular filtration rate (GFR) <60 ml/min required a dosage adjustment. Among the patients with GFR <60 ml/min, 83-90% received at least one drug that required a dosage adjustment and 67-70% received at least one drug that was potentially nephrotoxic, according to aMDRD or CG formulae, respectively. Five (50%) and 8 (47%) patients did not have appropriate MTX dosage adjustment according to their stage of KD with aMDRD or CG formulae, respectively., Conclusion: Systematic estimation of RF with CG or aMDRD formulae and urine dipstick are necessary in RA patients. In patients with KD at high risk for drug toxicity, dosage should be adapted to RF.

Methotrexate (MTX) has become the most commonly prescribed disease-modifying anti-rheumatic drug. However, toxicity is an important drawback of MTX therapy and permanent discontinuation of MTX for adverse effects occurs in 1 patient out of 10. Although high-dose MTX is known to be nephrotoxic, data on low-dose MTX renal effects are scanty. We report an insidious and progressive deterioration of renal function during long-term low-dose MTX in a 59-year-old woman. Kidney biopsy revealed advanced kidney fibrosis with extensive interstitial and glomerular fibrosis, and vascular sclerosis. We suggest that patients on low-dose MTX therapy even alone, should be periodically monitored for creatinine levels.