Electrolytically labeled [99mTc]MDP: chromatographic pattern, stability and biodistribution in rats

Biodistribution of anionic separated MDP complexes from different MDP preparations

The biodistributions of different Tc-MDP complexes, separated from different MDP preparations by anionic exchange chromatography, were investigated. We included MDP preparations from one producer with both ascorbic and gentisic acid as stabilizing agent and one preparation with ascorbic acid from a second producer. Bone to soft tissue ratios in rats were compared for the different Tc-MDP complexes separated. It seems that the elution profile of the radiochromatogram may indicate the biodistribution of the preparation. Ascorbic acid and gentisic acid caused different elution profiles and the different complexes isolated were demonstrated to have different bone to muscle ratios.

Localization of(99m)Tc in bone by means of autoradiography

The uptake of two different preparations of(99m)Technetium-methylene diphosphonate in fetal rat calvaria is compared. The localization of(99m)Tc after administration of(99m)Tc(Sn)-MDP and(99m)Tc-MDP showed equal distribution in autoradiography.

99mTc bone scanning agents--II. Adsorption of 99mTc(Sn)pyrophosphate complexes on the mineral phase of bone

The adsorption of pyrophosphate, tin-pyrophosphate and 99mTc(Sn)pyrophosphate on Ca3(PO4)2 was investigated at pH 4.0 and pH 7.4. All components were radioactively labeled. Tin and reduced technetium were in most cases almost completely bound. The adsorption of pyrophosphate, tin(II) and technetium-99m at pH 4.0 was higher than at pH 7.4. The presence of tin gave rise to an increase of the pyrophosphate adsorption that was much larger than can be accounted for by a stoichiometric adsorption of tin-pyrophosphate. It is concluded that tin and technetium are bound as negatively charged complexes with pyrophosphate. Finally it is argued that the fraction of the bone scanning agent that reaches the bone surface is adsorbed completely by the mineral phase.

Protein-binding and urinary excretion of 99mTc(Sn)-MDP and 99mTc-MDP

In an incubation experiment the Human Serum Albumin (HSA) binding of 99mTc-MDP (electrolytically labeled) and 99mTc(Sn)-MDP is established. During the incubation some pertechnetate is formed and in the case of 99mTc(Sn)-MDP also some hydrolyzed 99mTc. The HSA binding of 99mTc-MDP is less than the HSA binding of 99mTc(Sn)-MDP as established with gel chromatography, TCA-precipitation, ammonium sulfate precipitation and ultrafiltration. TCA-precipitation seems to be an insufficient method for determining the protein binding of 99mTc(Sn)-MDP. The urinary excretion in rats shows only one 99mTc-compound in both cases. The bone seeking properties of the urine-excreted 99mTc-compound were confirmed in another rat.