The elevation of N-acetyl-beta-D-glucosaminidase (NAG) in urine has been shown to be associated with reversible renal tubular damage.
The aim of the study was to examine the effect of first oral low dose methotrexate (MTX) on urinary excretion of NAG comparing with MTX concentration in serum and urine in a cohort of patients with rheumatoid arthritis (RA).
Urinary NAG to urinary creatinine ratio (NAG index) determined in 43 patients (5 males, 38 females) with RA who started taking the first oral dose of 10 mg of MTX. Urinary NAG index was observed at 24 h and 48 h after the first MTX dose. MTX concentration was measured in blood at 90 minutes and in blood and urine at 24 h after the drug administration.
NAG-enzymuria was increased in 72.1% of the patients before administration of MTX therapy (10.8 UI/g creatinine). There was no change in NAG index at 24 and 48 h after first dose of MTX (9.1 and 10.7 UI/g of creatinine). No differences of NAG-enzymuria in non-steroidal anti-inflammatory drug (NSAID)-treated patients and NSAID-free patients before and after MTX administration were revealed. The patients with decreased creatinine clearance had before treatment higher NAG index than those with normal creatinine clearance but there was not any significant increase of NAG activity after first dose of MTX in the patients with decreased creatinine clearance. Continued treatment with MTX resulted in a decrease in NAG activity accompanied by serum C-reactive protein concentration.
The use of low dose MTX with or without NSAIDs does not influence the renal tubular function in patients with RA.