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To improve the quality of 99mTc?methylenediphonate (99mTc?MDP) for skeletal imaging, different composed 99mTc?MDP complexes were prepared with addition of antioxidants such as ascorbic acid, getisic acid, and p-aminobenzoic acid. To characterize the different 99mTc?MDP preparations, some physical and biochemical properties of 99mTc?MDP such as thermal stability, lipophilicity and bindability to serum protein were studied and organ distribution pattern of these complexes also compared. The thermal stabilities of 99mTc?MDP contained antioxidants were dependant mainly on pH, temperature, and elapsed time after the preparation. 99mTc?MDP complex contained gentisic acid as antioxidant was extremely unstable at alkaline condition. The most stable 99mTc?MDP was found in the presence of p-aminobenzoic acid. 99mTc?MDP complexes with antioxidants were very lipophilic but lipophilicity differences in antioxidants were not observed. The bindability of 99mTc?MDP to serum protein was not affect at pH 5.0∼9.0 by the different antioxidants. However, protein binding percentage of 99mTc?MDP with ascorbic acid was relatively low (22.7%) at pH 9.0. In biodistribution studies in mice, bone to muscle ratios of 99mTc?MDP preparations containing ascorbic acid, gentisic acid, and p-aminobenzoic acid were 15.3, 24.5, and 30.1, respectively. Im to our results, p-aminobenzoic acid is fond to be the most promising antioxidant.
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