99mTc(CO)3(NTA) and 131I-OIH: Comparable Plasma Clearances in Patients with Chronic Kidney Disease

The pharmacokinetics of the tricarbonyl core radiopharmaceutical Tc-99m(CO)(3)-nitrilotriacetic acid (Tc-99m(CO)(3)(NTA)) in rats and subjects with normal renal function are comparable to those of I-131-o-iodohippuran (I-131-OIH), the radiopharmaceutical gold standard for the measurement of effective renal plasma flow. Our objective was to compare the pharmacokinetics of these 2 tracers in subjects with renal failure. Methods: Tc-99m (CO)(3)(NTA) was prepared with commercially available NTA and a commercially available labeling kit and isolated by reversed-phase high-performance liquid chromatography. Approximately 74 MBq (2.0 mCi) of Tc-99m(CO)(3)(NTA) were coinjected with approximately 11.1 MBq (300 mu Ci) of I-131-OIH in 8 subjects with stage 3-4 renal failure; simultaneous images were obtained for 24 min, followed by an anterior image over the gallbladder and abdomen. Plasma clearances were determined from 10 blood samples obtained 3-180 min after injection using the single-injection, 2-compartment model. Plasma protein binding, red cell uptake, and percentage injected dose in the urine at 30 and 180 min were determined. Results: There was no difference in the plasma clearances of Tc-99m(CO)(3)(NTA) and I-131-OIH (177 +/- 63 vs. 171 +/- 66 mL/min/1.73 m(2), respectively) (P = 0.41). The plasma protein binding and red cell uptake of Tc-99m(CO)(3)(NTA) were 35% +/- 7% and 6% +/- 3%, respectively; both values were significantly lower than the plasma protein binding (71% +/- 5%) and red cell uptake (16% +/- 2%) of I-131-OIH (P < 0.001). There was no significant difference in the percentage injected dose in the urine at 30 min (P = 0.24) and at 3 h (P = 0.82); for comparison, the percentage dose in the urine at 3 h was 77% +/- 9% for Tc-99m(CO)(3)(NTA) and 78% +/- 11% for I-131-OIH. Image quality with Tc-99m(CO)(3)(NTA) was excellent and no activity was identified in the gallbladder or intestine. Conclusion: Results in patients with renal failure show the clearance and rate of urine excretion of Tc-99m(CO)(3)(NTA) to be equivalent to that of I-131-OIH.