The effect of cyclosporine on urinary kallikrein excretion in patients with rheumatoid arthritis.

The effect of cyclosporine (6 to 8 mg/kg/24 hr) on urinary kallikrein excretion is summarized for 9 patients with rheumatoid arthritis using a specific kallikrein radioimmunoassay. Baseline serum creatinine and BUN values were within the normal range for all patients, and baseline kallikrein excretion rates were either normal (n = 5) or more than two S.D. below the mean of the normal group (n = 4). The patients with normal baseline values excreted significantly less urinary kallikrein three and six months after cyclosporine therapy was started, but all of them completed the six-month protocol. Patients in the subgroup with low baseline values also decreased their kallikrein excretion in response to cyclosporine therapy, and two of the four in this group experienced elevations of BUN such that therapy was terminated. In a low-dose (3 mg/kg/24 hr) open extension that followed the initial trial, kallikrein excretion decreased by almost 50% at least one month before any change in serum creatinine was observed. The data suggest that changes in urinary kallikrein excretion rates may be an indicator or predictor of cyclosporine nephrotoxicity. Decreased kallikrein excretion rates could also be a factor in the diminished renal blood flow reported in patients treated with cyclosporine.