TECHNETIUM-99M-ALENDRONATE - A NEW RADIOPHARMACEUTICAL FOR BONE SCANNING

The purpose of this paper is to report the preparation of a new techne tium-99m-radiopharmaceutical for bone scanning. The chelating agent fo r Tc-99m is a new bisphosphonate, alendronate, 4-amino-1-hydrogybutyli dene-1,1-bisphosphonate (ABP) used as a treatment for osteoporosis. AB P, because of its amino group, seems to be better suited to form a str ong and stable complex with technetium-99m and therefore might be bett er than Tc-99m-etidronate (HEDP) or Tc-99m-medronate (MDP) for bone sc anning. A sterile dry kit containing APE, a reducing agent and a stabi lizer was prepared. The parameters studied were molar concentrations, pH, shelf life, labeling efficiency and radiochemical purity. The oven dried sterile kit was formulated with 5 mg ABP, 0.25 mg stannous fluo ride and 0.025 mg gentisic acid at pH 2.5 - 3.5. The labeling efficien cy with 20 - 1500 MBq of pertechnetate ((TcO4-)-Tc-99m) was over 95% a t room temperature and was stable for 5 h. Technetium-99m-alendronate was tested in two rabbits and it proved to be a promising new radiopha rmaceutical for bone scanning. Work is underway to study Tc-99m-ABP bi odistribution in a statistically significant number of laboratory anim als and, later on, to determine radiopharmacokinetic parameters in. no rmal volunteers.