[Pharmacokinetics of 99mTc-MAG3 and 131I-OIH: comparative study based on 2 compartment model analysis]

We studied 50 patients with mild to moderate renal dysfunction to compare pharmacokinetics of 99mTc-MAG3 with that of 131I-OIH. After simultaneous bolus injection of both 99mTc-MAG3 and 131I-OIH, 8-point venous blood sampling was performed from 2 to 44 min post injection. Aliquoted plasma samples were counted for radioactivity along with the injected standard to obtain % injected dose/ml plasma for each tracer. Using obtained time-concentration data, classical 2 compartment model analysis was performed for both tracers to obtain various pharmacokinetic parameters, including distribution volumes (Vds), inter-compartmental rate constants, and plasma clearance. In these parameters, Vd of central compartment, Vd at steady state, central to peripheral inter-compartmental rate constant, and plasma clearance were significantly larger for 131I-OIH. In all parameters, significant correlation was found between 99mTc-MAG3 and 131I-OIH. The best correlation was seen in plasma clearance (r = 0.891, p < 0.0001). Plasma clearance ratio (99mTc-MAG3/131I-OIH), however, showed weak but significant negative correlation with serum creatinine, although this correlation was not likely to affect the overall correlation of clearance between 131I-OIH and 99mTc-MAG3. From these results, we confirmed that 99mTc-MAG3 clearance could be used as an alternative to 131I-OIH clearance, although pharmacokinetic behavior of 99mTc-MAG3 was not exactly the same as that of 131I-OIH.