Pre-ZA dental screenings were documented in 14% of standard-interval patients and 17% of extended-interval patients, and during-ZA screenings were documented in 17% of standard-interval patients and 20% of extended-interval patients. Chi-square analysis revealed no significant difference in rates of dental screening before or during use of ZA.
Standard-interval patients received a mean (SD) 11.4 (13.5) doses of ZA (range, 2-124). Extended-interval patients received a mean (SD) of 5.9 (3.18) doses (range, 2-14). All standard-interval patients had discontinued treatment at the time of the study, most commonly because of death or for an unknown reason. Sixty percent of extended-interval patients had discontinued treatment, most commonly because of patient/physician choice or for an unknown reason (Table 2).
Skeletal-related events were observed in 31% of standard-interval patients and 23% of extended-interval patients. There were no statistically significant differences in SRE rates between groups (P = .374). The most common SRE in both groups was bone irradiation (42% and 60%, respectively), with no statistically significant difference in proportion between groups (Table 4).
Discussion
This retrospective review of patients with MM and CaP receiving ZA for bone metastasesfound no differences in the rates of SREs when ZA was dosed monthly vs every 3 months.
Earlier studies found that ZA can decrease SRE rates, but a major concern is that frequent, prolonged exposure to IV bisphosphonates may increase the risk of ONJ. No significant differences in ONJ rates existed between dosing groups, but all documented cases of ONJ occurred in the standard-interval group, suggesting a trend toward decreased incidence with an extension of the dosing interval.
Limitations
This study had several limitations. Geriatric African American men comprised the majority of the study population, and patients with MM accounted for only 22% of included regimens, limiting external validity. Patient overlap between groups may have confounded the results. The retrospective design precluded the ability to control for confounding variables, such as concomitant medication use and medication adherence, and significant heterogeneity was noted in rates of adherence with ZA infusion schedules regardless of dosing group. Use of medications associated with increased risk of osteoporosis—including corticosteroids and proton pump inhibitors—was not assessed.
Assessment of ONJ incidence was limited by the lack of access to dental records from providers outside the VA. Many patients in this review were not eligible for VA dental benefits because of requirements involving time and service connection, a reimbursement measurement that reflects health conditions “incurred or aggravated during active military service.”18
The results of this study provide further support for extended-interval dosing of ZA as a potential method of increasing patient adherence and decreasing the possibility of adverse drug reactions without compromising therapeutic benefit. Further randomized controlled trials are needed to define the potential decrease in ONJ incidence.