N-acetyl-beta-D-glucosaminidase enzymuria as an indicator in monitoring the therapy of some rheumatic diseases with potentially nephrotoxic drugs.

The measurement of NAG enzymuria by the spectrofluorimetric assay according to Merle et al. enables an early diagnosis of tubular dysfunction. Urinary NAG activity was determined in 13 patients with various rheumatic diseases during administration of potentially nephrotoxic drugs like nonsteroidal anti-inflammatory drugs (NSAID), aminoglycosides, gold salts, cyclosporin and steroids. The significant decrease of urinary NAG activity was common in patients with recently diagnosed rheumatic diseases, who received steroids. The decrease of NAG enzymuria was correlated with biochemical indices of inflammation like ESR or hemoglobin. The use of two types of potentially nephrotoxic drugs, like NSAID and gentamicin or NSAID with cyclosporin induced significant augmentation of NAG excretion. This occurrence may precede azotemia. The recognition of high NAG enzymuria permits to reduce dosage or discontinue treatment with potentially nephrotoxic drug prior to irreversible renal insufficiency as shown in the case of a patient with psoriatic arthritis treated with simultaneously administered cyclosporin and diclofenac.