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Clinical Comparison of the Kinetics of ^99mTc-Labeled Polyphosphate and Diphosphonate

VA Wadsworth Hospital Center, UCLA School of Medicine, and School of Pharmacy, University of Southern California, Los Angeles, California

Correspondence: For reprints contact: G. T. Krishnamurthy, Nuclear Medicine Service, VA Wadsworth Hospital Center, Los Angeles, Calif. 90073.

ABSTRACT

Kinetics of ^99mTc-labeled polyphosphate and diphosphonate (disodium ethane-1-hydroxy-1, 1-diphosphonate) are studied and compared clinically in ten patients in a paired study. Four hours after injection, both agents show a biexponential type of blood clearance. The Exponent I represents bone uptake and the Exponent II, mainly the renal excretion. The clearance of diphosphonate is relatively faster than that of polyphosphate resulting in significantly lower blood background radioactivity. Both agents show identical plasma protein fraction binding and 4-hr urinary excretion. The kidneys are well visualized with both agents, consistently better with polyphosphate. The sensitivity for the detection of lesions is similar for both. At the end of 4 hr, 10% of the dose of ^99mTc-polyphosphate is circulating in the blood, 33.3% is excreted in urine, and the remaining 56.3% is taken up by bone and other tissues. The corresponding values with ^99mTc-diphosphonate are: 7.0% in blood, 33.8% in urine, and 59.2% in bone and other tissues. It is concluded that both ^99mTc-labeled polyphosphate and diphosphonate are excellent skeletal-imaging agents and have equal sensitivity. No toxic reactions are noted with either agent.