Prevalence of Non-Responders to Both Oral Bisphosphonate Monotherapy and Intravenous Ibandronate in Patients with Postmenopausal Osteoporosis

Objectives: Although bisphosphonates (BPs) are effective for the majority of patients with osteoporosis, some individuals do not adequately respond to these drugs. The objective of this study was to estimate the prevalence of true BP non-responders who showed insufficient response after both oral BPs and intravenous ibandronate. Methods: Among 146 consecutive patients with postmenopausal osteoporosis who received oral BP monotherapy for more than 12 months, insufficient responders to oral BP monotherapy were switched to intravenous ibandronate injection and followed for more than 12 months. Serum N-terminal telopeptide of type I collagen (NTX) and bone alkaline phosphatase (BAP) concentrations were measured. Patients who also showed insufficient response to intravenous ibandronate were defined as true BP non-responders. Insufficient response to BP therapy was evaluated based on the serum NTX reduction cut-off for minimum significant change. Results: Sixty-one patients (41.8%) were diagnosed as oral BP non-responders. Fourteen patients who switched to intravenous ibandronate and had complete data available were used for final analysis. After switching to intravenous ibandronate, both NTX and BAP decreased significantly (p < 0.05). However, at 6 - 12 months after switching, 57.1% - 64.3% of patients still showed insufficient response of NTX as compared to baseline (before oral BP monotherapy), and 21.4% - 35.7% of patients still showed insufficient response of NTX when compared to data immediately before switching. Conclusion: These results estimated that as few as 9% - 15% (i.e., 21.4% - 35.7% of 41.8%) or as many as 24% - 27% (i.e., 57.1% - 64.3% of 41.8%) of patents might be true BP non-responders.