COMPARATIVE EVALUATION OF 3 DIPHOSPHONATES - INVITRO ADSORPTION (C-14-LABELED) AND INVIVO OSTEOGENIC UPTAKE (TC-99M COMPLEXED)

  • 1 January 1980
    • journal article
    • research article
    • Vol. 21  (12) , 1185-1189
Abstract
The in vitro adsorption of 3 14C-labeled diphosphonates on calcium phosphate was studied. The 3 are 1-hydroxy[1-14C]ethylidene diphosphonate (C-14 HEDP), [14C]methylenediphosphonate (C-14 MDP) and hydroxy[14C]-methylenediphosphonate (C-14 HMDP). All 3 adsorbed significantly more, per mole of Ca, on amorphous calcium phosphate than on crystalline hydroxylapatite. Among the 3 diphosphonates, C-14 HMDP adsorbed, on both amorphous and crystalline calcium phosphate, to a greater degree than did the other 2 bone-seeking agents. When HMDP was complexed with Sn(II) and 99mTc, it produced a significantly higher uptake of 99mTc per mg of Ca, in an isolated in vivo in rats site of osteogenesis. The mechanisms of adsorption are discussed relative to the hydroxyl group on the diphosphonate, to the solubility of the Ca salts of the diphosphonates and to the form of the calcium phosphate. These studies form a working rationale for the clinically observed high contrast obtained with 99mTc HMDP between normal bone and soft tissue, and between normal and abnormal bone.