99mTc-aprotinin: a new tracer for kidney morphology and function

Aprotinin (Ap), a low-molecular-weight polypeptide (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 99mTc. 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 99mTc-Ap and with 99mTc-DMSA. 99mTc-Ap was slightly better than 99mTc-DMSA, especially in patients with far advanced renal failure. Some aspects of the pharmacokinetics of 99mTc-Ap were studied in 72 cases. In 22 of these patients plasma clearance of 99mTc-Ap was determined by the single injection method using a two-compartment model. In patients with GFR greater than 90 ml/min plasma clearance of 99mTc-Ap was 67.6 +/- 8.4 SD ml/min. A good correlation was observed between plasma clearance of 99mTc-Ap and GFR (r = 0.74). After IV injection 99mTc-Ap was stably fixed by the kidney. Renal radioactivity remained stable between the second and eighth hour after the injection. Urinary excretion of radioactivity measured in 35 patients in the first and in the second 2-h interval after IV injection of 99mTc-Ap was negligible in all patients (2.7 +/- 1.5 SD percent of the dose in the first 2 h; 2.8 +/- 1.4 SD between the second and fourth hour). 99mTc-Ap is an excellent agent for renal imaging. It also seems promising for renal function studies.