A study of the relationship between chemical structure and bone localization of Tc-99m diphosphonic acids: concise communication.

The study was undertaker to evaluate the effect on bone localization of substitutions at the bridge carbon atom of methylenediphosphonic acid. Two monosubstituted compounds (ethylidenediphosphonic acid and benzylmethylenediphosphonic acid), and one disubstituted compound (isopropylidenediphosphonic acid), were synthesized. The biological behavior was compared with that of MDP and dichloro-MDP in the rat, using Tc-99m as a label. Ethylidenediphosphonic acid showed the highest femur-to-liver and femur-to-muscle ratios. MDP exhibited a slightly faster blood clearance than ethylidenediphosphonic acid.