Tc-99m MDP and Tc-99m HEDP are the conventional bone scintigraphy agents widely used for the last 30 years. Since then, a variety of new phosphonates including alendronate have replaced the older ones because of higher efficacy in bone disorders. In the present study we propose a method to radiolabel alendronate with Tc-99m and compare it with conventionally available agent (Tc-99m MDP) for bone imaging.
Ready to use alendronate kits were produced using stannous chloride reduction method. The kit underwent in vitro and in vivo quality control tests in animals followed by human trial in more than 35 subjects. In many cases, both Tc-99m alendronate and Tc-99m MDP scans were done.
More than 98% radiolabeling was consistently achieved. Serum studies showed 47% protein binding and stability of the preparation up to 24 h. Animal biodistribution studies and blood clearance data supports similar bone uptake and faster blood clearance as compared to Tc-99m MDP. Bone scintigraphy with Tc-99m alendronate in humans suggests acceptable bone to soft tissue ratio at 90–120 min.
The proposed method of radiocomplexation of alendronate is a viable option for preparing this radiopharmaceutical. Tc-99m alendronate gives acceptable images at 90–120 min post injection compared to 3–4 hrs with Tc-99m MDP. It has the potential to become an important bone-imaging agent because of easy availability, cost-effectiveness and the fact that MDP is now obsolete and may not be available easily as a drug.
Alendronate, Technetium-99m, Bisphosphonates, Scintigraphy
