Objective: This study was aimed at monitoring the early and late effects of infliximab on renal proximal function in RA patients treated with methotrexate. N-acetyl-3-D-glucosaminidase (NAG) activity in urine served as an indicator of proximal tubular damage
Methods: NAG activity was estimated in 21 patients during the course of treatment with infliximab and methotrexate. In every patient NAG-enzymuria was estimated directly before and 60 min after infliximab infusions and 62 weeks after starting the therapy.
Results: The total of mean NAG activities observed before each infusion of infliximab was significantly lower (p < 0.02) than NAG-enzymuria before the start of infliximab treatment (7.4 UI/g vs 11.8 UI/g). The proportion of patients in whom NAG activity rose by more than 50% during treatment ranged from 5.3% to 25%. Administration of infliximab did not significantly change the mean serum creatinine levels or creatinine clearance. No significant differences were observed in the mean values of NAG values before and 60 min after infliximab infusion. Patients who demonstrated elevated NAG activities during the course of the whole treatment demonstrated significantly more pronounced NAG enzymuria before treatment and one hour after the first infusion (p < 0.0005), as well as higher RA activity (p < 0.05). There was no observed influence of NSAIDs or prednisone on the frequency of elevated NAG activities. Raised creatinine concentrations (> 1.3 mg/dL) were noted before and during the course of infliximab treatment in 3 patients. In 16 patients abdominal fat aspiration biopsy was performed and in 3 the presence of amyloid deposits was demonstrated. In these patients NAG activity exceeded twice the upper normal limit.
Conclusion: The introduction of infliximab during methotrexate therapy demonstrated no early or delayed nephrotoxicity of the drug in patients with rheumatoid arthritis.