title: Pharmaco-kinetics of current skeletal-seeking radiopharmaceuticals.
abstract: The blood clearance of all current bone-seeking radiopharmaceuticals is biexponential during the first four hours after injection. Exponent I represents bone uptake and its clearance half-time is less than 30 min. Exponent II represents mainly urinary excretion and its clearance half-time varies from 168 to 512 min. The blood background is highest with 99mTc-labeled polyphosphate (Tc-Poly) and lowest with sodium fluoride (F-18); 99mTc-labeled diphosphonate (Tc-Dip) and 99mTc-labeled pyrophosphate (Tc-Pyro) show intermediate blood levels. The slower blood clearance of 99mTc-phosphate complexes in comparison with F-18 is due primarily to their increased protein binding. Tc-Poly blood clearance, which is slower than that of Tc-Dip and Tc-Pyro, is due primarily to its increased red cell binding and the larger size of its molecule. Bone uptake and urinary excretion of all 99mTc-labeled phosphate complexes are approximately the same: in the range of six to ten per cent in the blood, 30-33% in the urine, and 55-58 percent in the bone and other tissues. F-18 concentration in the bone is almost 1.5 times that of the 99mTc-labeled phosphate complexes. The sensitivity and resolution of lesions are identical for all 99mTc-labeled phosphate complexes and are far better than those for F-18. No toxicity is noted with the amount of phosphate present in the marketed kits, and it appears reasonable to use the minimal amount so long as efficiency is not compromised.
mesh_terms: D001702:Biopharmaceutics; D001842:Bone and Bones / Q000378:metabolism*; D002986:Clinical Trials as Topic; D011756:Diphosphates / Q000378:metabolism; D005461:Fluorine / Q000378:metabolism; D006801:Humans; D007553:Isotope Labeling; D007700:Kinetics; D008657:Metabolic Clearance Rate; D010710:Phosphates / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism*; D011868:Radioisotopes; D011877:Radionuclide Imaging; D013667:Technetium / Q000378:metabolism*
chemical_list: D011756:Diphosphates; D010710:Phosphates; D011868:Radioisotopes; D010758:Phosphorus; D005461:Fluorine; D013667:Technetium