Increased renal tubular cell excretion by patients receiving chronic therapy with gold and with nonsteroidal anti-inflammatory drugs. 
Using rheumatoid arthritis patients who were receiving gold as models, we evaluated the renal effects of the chronic administration of very low doses of a nephrotoxic drug.  The heavy metal gold has been shown to increase urinary enzyme excretion when it is given in usual doses for the treatment of rheumatoid arthritis.  It is not clear whether the increased urine enzyme excretion caused by long-term drug therapy represents injury to the kidney or whether it is merely an effect of the drug.  Urinary N-acetyl-beta-glucosaminidase and renal tubular cell excretion rates were measured in 19 patients who were receiving chronic treatment with gold and with nonsteroidal anti-inflammatory drugs for rheumatoid arthritis, in 10 patients who were receiving nonsteroidal anti-inflammatory drugs, and in 8 healthy control subjects.  No subjects showed evidence of kidney disease.  Both renal tubular cell and enzyme excretion rates were elevated in the gold-treated group.  This showed that there was increased renal tubular cell turnover in this group, which suggests low level renal tubular injury and not merely an effect of the usual dose of gold.