Alendronate does not interfere with Tc-99m-methylene diphosphonate bone scanning

Several studies have found that administration of etidronate results in com petitive interference with Tc-99m-labeled bone scanning reagents. In contra st, in other studies this problem was not encountered with other bisphospho nates. Methods: We prospectively studied 9 patients with hormone-refractory prostate cancer. Tc-99m-methylene diphosphonate (MDP) bone scanning was pe rformed before they received alendronate, and scanning was repeated a mean of 16.6 d afterward, when the patients had been receiving 40 mg alendronate daily for a mean of 6 d. In addition, 7 patients who underwent delayed sca nning when they had been receiving alendronate for a mean of 111 d were als o restudied. Quantitative whole-body bone scanning was performed, and radio activity deposited in the bone metastasis was determined using region-of-in terest analysis. Results: A <6% increase in whole-body retention of Tc-99m- MDP was seen on the initial postalendronate scan compared with the baseline scan. No significant differences in activity were seen in the bone lesion evaluated on the baseline and initial postalendronate studies. The delayed postalendronate scan generally showed similar or higher tracer accumulation compared with the baseline scan. Conclusion: Alendronate did not competiti vely inhibit uptake of Tc-99m-MDP in the skeleton or tumor metastasis. Use of alendronate before bone scanning is unlikely to result in decreased dete ction of lesions or falsely decreased Tc-99m-MDP activity at metastatic bon e tumor sites.