/sup 99m/Tc-aprotinin: A new tracer for kidney morphology and function

Aprotinin (Ap), a low molecular weight polyeptide (6500 dalton), is a protease inhibitor which is electively and stably accumulated in the kidney. In 112 adult patients, with either uni- or bilateral renal disease with different degrees of renal impairment (from normal GFR to advanced renal failure), renal scans were performed by means of Ap labelled with /sup 99m/Tc. Highly satisfactory renal scans were obtained in all patients. In 20 patients with renal failure (serum creatinine 1.8 - 8.5 mg/dl, mean 4.7) a comparison was made of the renal scans obtained with /sup 99m/Tc-Ap and with /sup 99m/Tc-DMSA. /sup 99m/Tc-Ap was slightly better than /sup 99m/Tc-DMSA, especially in patients with far advanced renal failure. Some aspects of the pharmacokinetics of /sup 99m/Tc-Ap were studied in 72 cases. In 22 of these patients plasma clearance of /sup 99m/Tc-Ap was determined by the single injection method using a two-compartment model. In patients with GFR>90 ml/min plasma cl of /sup 99m/Tc-Ap was 67.6 +- 8.4 SD ml/min. A good correlation was observed between plasma clearance of /sup 99m/Tc-Ap and GFR (r = 0.74). After i.v. injection /sup 99m/Tc-Ap was stably fixed by the kidney. Renal radioactivity remained stable between the 2nd and the 8th hour after the injection. Urinary excretion of radioactivity measured in 35 patients in the first and in the second 2-hour interval after i.v. injection of /sup 99m/Tc-Ap was negligible in all patients (2.7 +- 1.5 SD percent of the dose in the fist 2 hours; 2.8 +- 1.4 SD between the 2nd and the 4th hour). Conclusions. /sup 99m/Tc-Ap is an excellent agent for renal imaging. It also seems promising for renal function studies