e19507 Background: Ibandronate is a third generation bisphosphonate with analgesic effects demonstrated in previous phase III trials. Renal safety of ibandronate enables using higher-dose regimens. We aimed to investigate whether high doses of ibandronate is effective and safe in patients with breast cancer and bone metastases suffering from moderate to severe pain. Methods: Female breast cancer patients with moderate to severe metastatic bone pain diagnosed with visual analogue scale (VAS) >5 (range: 0 (no pain) to 10 (maximum pain)) were included in this phase II single arm multicenter study. Patients were treated with intravenous ibandronate 6mg infused over 15 minutes on 3 consecutive days. Patient visits were made on days 1, 2, 3, 4, 7, and 14, and vital signs, physical examination, analgesics used, blood counts and serum biochemistries, pain assessment with VAS and Karnofsky performance status were evaluated. Patients were given diaries to rate the intensity of pain on a VAS chart and note the analgesics they have used daily for 14 days. Results: Thirteen patients were included in the study. Median age was 51. Five patients (30,8%) had a history of bisphosphonate use. The rate of analgesic use was 69,2%, 0%, 7,7%, 15,4%, 16,7% and 15,4% on days 1, 2, 3, 4, 7 and 14, respectively. Pain intensity based on VAS scores significantly decreased on day 7 (3.2 ± 2.2, p<0.01) and day 14 (3.0 ± 2.1, p<0.01) compared with day 1 (6.1±0.9). Time to pain response was 8.2 days in ITT population. Adverse events were observed in 5 patients (38.5%), with vomiting being the commonest one, and with mild to moderate severity in most cases. Only one patient (7.7%) experienced severe headache, which spontaneously resolved on follow up. Majority of the adverse events were deemed unrelated to the study drug. No serious adverse events were observed. No significant change was detected in laboratory parameters throughout the study. Conclusions: Administration of loading dose ibandronate resulted in significant reduction in bone pain and analgesic use by the patients. The intensive dosing schedule was not associated with any deterioration in renal function and was generally well tolerated. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Roche Pharma AG