Pharmacokinetics in Intact Rats of N,N,N′,N′-Ethylenediaminetetrakis-(Methylenephosphonic Acid) Labeled with Gallium-68

Abstract

Pharmacokinetic studies of the new bone-seeking radiopharmaceutical (RP) ⁶⁸Ga-labeled N,N,N′,N′-ethylenediaminetetrakis(methylenephosphonic acid) (EDTMP) for PET diagnosis of bone metastases showed that ⁶⁸Ga-EDTMP accumulated rapidly in bone 1 h after i.v. injection, e.g., up to 3.55 ± 0.20%/g in femur, 2.24 ± 0.13%/g in vertebrae, 2.00 ± 0.21%/g in rib, and 1.81 ± 0.10%/g in skull, was cleared rapidly from blood, and had minimal uptake in internal organs and tissues. Most of the activity was excreted through the urinary tract. Knee joints also had significant ⁶⁸Ga-EDTMP accumulations. It was found that the bone concentration of ⁶⁸Ga-EDTMP was significantly greater than that of ⁶⁸GaCl₃ (p < 0.001 – 0.05). The ratios of specific activity in bone to those in organs and tissues (differential accumulation factors, DAFs) were greater than unity at all time points. For example, the maximum femur/blood and femur/muscle ratios were 8.00 ± 1.31 and 43.1 ± 7.4. Thus, ⁶⁸Ga-EDTMP could be considered a potential RP for PET imaging of bone damage.