(99m)Tc(CO)3(NTA): a (99m)Tc renal tracer with pharmacokinetic properties comparable to those of (131)I-OIH in healthy volunteers.

Unlabelled: Studies in rats showed that the pharmacokinetics of the tricarbonyl core radiopharmaceutical (99m)Tc(CO)(3)-nitrilotriacetic acid, (99m)Tc(CO)(3)(NTA), were essentially identical to those of (131)I ortho-iodohippuran ((131)I-OIH), the clinical gold standard for the measurement of effective renal plasma flow. Our objective was to compare the pharmacokinetics of these 2 tracers in healthy volunteers.
Methods: (99m)Tc(CO)(3)(NTA) was prepared with commercially available NTA and a commercially available kit and isolated by reversed-phase high-performance liquid chromatography. Approximately 74 MBq (2 mCi) of (99m)Tc(CO)(3)(NTA) were coinjected with 9.25 MBq (250 microCi) of (131)I-OIH in 9 volunteers, and simultaneous imaging of each tracer was performed for 24 min. Plasma clearances were determined from 8 blood samples obtained 3-90 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 (99m)Tc(CO)(3)(NTA) and (131)I-OIH, 475 +/- 105 mL/min versus 472 +/- 108 mL/min, respectively. The plasma protein binding and red cell uptake of (99m)Tc(CO)(3)(NTA) were 43% +/- 5% and 9% +/- 6%, respectively; both values were significantly lower (P < 0.001) than the plasma protein binding (75% +/- 3%) and red cell uptake (17% +/- 5%) of (131)I-OIH. There was no significant difference in the percentage injected dose recovered in the urine at 30 min and at 3 h; for comparison, the percentage dose in the urine at 3 h was 91% +/- 4% for (99m)Tc(CO)(3)(NTA) and 91% +/- 6% for (131)I-OIH (P = 0.96). Image quality with (99m)Tc(CO)(3)(NTA) was excellent, and the renogram parameters were similar to those of (131)I-OIH.
Conclusion: Preliminary results in healthy volunteers suggest that the pharmacokinetic behavior of (99m)Tc(CO)(3)(NTA) is comparable to that of (131)I-OIH.