Complexes of technetium-99m with phosphomycin, obtained by pH shifting: biological characteristics, whole-body...

Phosphomycin (phos), a large spectrum antibiotic with preferential localization into the kidneys, can be labeled with technetium-99m at various pHs. However, the final pH in the labeling of phos by [99mTc]pertechnetate in the presence of SnCl2 seems to play a significant role in determining the biological properties of the final labeled product. Radiopharmacological characteristics of various forms of 99mTc-phos obtained at pHs 6.8, 4.5 and 2.5 were studied in mice, rats and rabbits. Significant differences in these products were shown by biodistribution studies in Balb/C mice and Wistar rats and confirmed by whole-body autoradiographies in mice and gamma-camera studies in rats and rabbits. 99mTc-phos, pH 6.8, has a high uptake in kidneys from 2 min after injection (10.25 +/- 1.11 %ID) to 3 h after injection (8.26 +/- 0.42 %ID) and a rapid urinary excretion (19.9 +/- 7.35 %ID at 2 min after injection and 75.11 +/- 3.48 %ID at 3 h). Intrarenal pharmacokinetics studied by autoradiography showed a high concentration in the inner medulla and pelvis at 1 min after injection followed by an increased localization in kidney cortex, like 99mTc-DMSA. Preferential uptake in bones was shown by 99mTc-phos, pH 2.5, from 5 min to 3 h after injection (15.05 +/- 2.67 %ID at 3 h compared to 1.79 +/- 0.19 %ID of 99mTc-phos, pH 6.8, at the same time). A high urinary excretion of 99mTc-phos, pH 2.5, is shown as in the case of other bone agents (76.5 +/- 3.46 %ID at 3 h post-injection) but without any kidney retention (1.80 +/- 0.26 %ID in kidneys 3 h post-injection).(ABSTRACT TRUNCATED AT 250 WORDS)