Optimal Timing of Bisphosphonate Administration in Combination with Samarium-153 Oxabifore in the Treatment of Painful Metastatic Bone Disease

While bisphosphonates are indicated for prevention of skeletal-related events, radionuclide therapy is widely used for treatment of painful bone metastases. Combined radionuclide therapy with bisphosphonates has demonstrated improved effectiveness in achieving bone pain palliation in comparison to mono therapy with radionuclides or bisphosphonates alone. However, there are conflicting reports as to whether bisphosphonates adversely influence skeletal uptake of the bone-seeking radiotracers used for therapy. Recent studies analyzing influence of Zoledronic acid on total bone uptake of Samarium-153 EDTMP (Sm-153 EDTMP) by measuring cumulative urinary activity of Sm-153 on baseline study, as well as in combination with bisphosphonates (administrated 48 hours prior to Sm-153) did not provide any statistically significant difference in urinary excretion of Sm-153 between the two groups. It may be noted that the exact temporal sequence of bisphosphonate administration vis a vis radionuclide therapy has not yet been studied. One of the side effects of bisphosphonates is transient flare effect on bone pain. Radionuclide therapy may also have similar side effect. Keeping in view the above the current study was designed with the main objective of determining the exact timing of bisphosphonate administration in patients receiving combined therapy so as to achieve optimal efficacy of bone pain palliation. Ninety-three patients suffering from metastatic bone pain who received combination therapy with Sm-153 oxabifore (an analog of Sm-153 EDTMP) and Zoledronic acid were divided into three groups according to the timing of Zoledronic acid administration: Group I: 39 patients who received Zoledronic acid 7 or more days prior to Sm-153 oxabifore treatment; Group II: 32 patients who received Zoledronic acid 48-72 hours prior to Sm-153 oxabifore treatment and Group III: 22 patients who received Zoledronic acid 7 days after Sm-153 oxabifore treatment. Sm-153 oxabifore was administered to all patients at the standard bone palliation dose of 37 MBq/kg body weight. All patients received Zoledronic acid before and after treatment in standard dosage of 4 mg every 28 days. WB bone scan, CT, and MRI were performed before treatment in all patients to exclude cord compression and vertebral fractures. Pain scores and quality of life (QOL) measurements were recorded meticulously in all patients. In groups I, II, and III, pain relief occurred in 10.4 ± 3.1 (Range = 5-15); 3.1 ± 1.1 (Range = 1-5) and 22 ± 5.1 (Range = 15-35) days, respectively, following radionuclide therapy. There was statistically significant difference between pain score in all groups before and after treatment as well as statistically significant difference in time to pain relief onset between Group II and other groups of patients ( P < 0.0001). Based on our results we concluded that administration of Zoledronic acid 48-72 hours prior to Sm-153 oxabifore treatment helps in achieving better pain relief, as well as at the shortest time interval from the start of therapy.