Is (99m)Tc-labelled pamidronate a better agent than (99m)Tc-medronate for bone imaging?
OBJECTIVE
To evaluate the potential of (99m)Tc-pamidronate ((99m)Tc-APD) against (99m)Tc-medronate ((99m)Tc-MDP) as a new bone-seeking agent using intact bone and fractured femur in a rat model.


METHODS
(99m)Tc-APD was prepared by the stannous reduction method. Scintigraphic images were obtained at 2 h and 24 h after intravenous injection of (99m)Tc-APD or (99m)Tc-MDP in rats, then they were culled to estimate activities in various organs. Bone uptake (as percent injected dose/gram weight) was estimated in an intact femur and in 1 week post-fracture model. The urinary excretion dose (as percent injected dose) was also estimated.


RESULTS
The bone uptake of (99m)Tc-APD was significantly higher (P<0.05) than (99m)Tc-MDP at 2 h and 24 h post-injection studies. (99m)Tc-APD uptake was further increased (P<0.05) in the fracture model than the intact femur. (99m)Tc-APD uptake in the soft tissues including liver and the kidneys was lower than (99m)Tc-MDP. Renal excretion was faster and the ratios of bone to blood and bone to soft tissues were higher with APD than MDP. APD dose was selected at 1% of MDP, to obviate therapeutic effect, as the former compound is 100 times more potent than MDP.


CONCLUSIONS
Our results suggest that (99m)Tc-APD uptake by intact bone and fractured bone was significantly higher than (99m)Tc-MDP. The renal clearance of (99m)Tc-APD was faster and soft tissue uptake was lower than (99m)Tc-MDP. These results suggest that APD has the potential to become an excellent bone-imaging agent.
Kumar
Vijay
V
Department of Nuclear Medicine, Westmead Hospital, NSW 2145, Australia. nvk@imag.wsahs.nsw.gov.au
Kumar
Divesh
D
Howman-Giles
Robert B
RB
Little
David G
DG
D000818:Animals; D001842:Bone and Bones / Q000473:pathology*; D004164:Diphosphonates / Q000493:pharmacokinetics; D005269:Femur / Q000473:pathology; D050723:Fractures, Bone / Q000473:pathology; D008297:Male; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D011877:Radionuclide Imaging / Q000295:instrumentation* / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D017208:Rats, Wistar; D013669:Technetium Tc 99m Medronate / Q000493:pharmacokinetics; D013997:Time Factors
D004164:Diphosphonates; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C039598:technetium Tc 99m 3-amino-1-hydroxypropane-1,1-diphosphonate; D013669:Technetium Tc 99m Medronate