Evaluation of two different HEDP content kits: stability study against dilution both in vivo and in vitro

Two different HEDP content kits (Kit A, HEDP: 1 mg, SnCl2. 2H2O: 0.5 mg; and Kit B, HEDP: 10 mg, SnCl2. 2H2O: 0.5 mg) were evaluated for their stability against dilution 99mTc-HEDP solutions prepared from these two kits were diluted from 10 to 6000fold with 0.9% NaCl solution just before evaluation both in vivo and in vitro. In the case of Kit A, significant soft tissue uptake in vivo and released free pertechnetate in vitro were observed by diluting the 99mTC-HEDP solution. On the other hand, 99mTc-HEDP prepared from Kit B was found to be sufficiently stable against dilution. The stability after preparation of each diluted 99mTc-HEDP was also greatly affected by its HEDP concentration. Preliminary analysis of absorption spectra for each 99Tc-HEDP indicated the possibility of two different 99mTc-HEDP complex formation by varied HEDP concentration. These results indicated that a cold reagent like Kit A might cause a higher soft tissue uptake due to its dilution in vivo during a clinical study for bone scanning.