One versus 2 years of alendronate following denosumab: the CARD extension.

When denosumab is discontinued, antiresorptive therapy is critical to reduce high-turnover bone loss. The ideal duration of antiresorptive therapy after denosumab is uncertain. This study demonstrates that both 1 and 2 years of alendronate maintained bone density gains achieved with 1 year of denosumab.

Background: When denosumab is discontinued, antiresorptive therapy is critical to attenuate high-turnover bone loss. The ideal choice and duration of antiresorptive therapy are not yet defined, however. In the Comparison of Alendronate or Raloxifene following Denosumab (CARD) study, we demonstrated that 12 months of alendronate was better able to maintain the bone mineral density (BMD) gains achieved with 12 months of denosumab versus 12 months of raloxifene. In this extension, we wished to determine if 12 months of alendronate would be sufficient in maintaining these denosumab-induced BMD gains.

Methods: In the CARD study, postmenopausal osteoporotic women aged 60-79 at high fracture risk received 12 months of denosumab 60-mg SC every 6 months followed by 12 months of either alendronate 70 mg weekly (N = 26) or raloxifene (N = 25). All subjects in the alendronate arm were then offered participation in a 1-year extension in which they were randomized to continue alendronate for an additional 12 months (N = 10) or to receive calcium and vitamin D alone (N = 8). The primary outcome was change in spine BMD between months 24 and 36. Exploratory endpoints included changes in areal BMD (aBMD) at other anatomic sites as well as changes in serum bone turnover markers.

Results: The CARD study demonstrated the effectiveness of 12 months alendronate in preserving denosumab-induced BMD gains. In the extension, aBMD was maintained at the spine, total hip, and femoral neck in both those randomized to an additional year of alendronate and those randomized to calcium/vitamin D alone. We did, however, observe a transient comparative decrease between months 24-30 in the calcium/vitamin D group at the total hip (P = 0.008) and femoral neck (P = 0.040). At the end of 24 months of the CARD study, bone turnover markers serum c-telopeptide (CTX) and procollagen N-propeptide of type I collagen (PINP) were suppressed in both groups and then increased more between months 24-36 in the calcium/vitamin D group than the alendronate group (P = 0.051 for CTX, P = 0.030 for P1NP). Both CTX and PINP remained below the month 0 baseline in both groups (P < 0.05 for all comparisons).

Conclusions: With the limitations of our small sample size, these data suggest that both 1 and 2 years of alendronate effectively maintain BMD gains achieved with 1 year of denosumab and prevented any rebound in bone turnover marker levels above pre-denosumab baseline. This is the first randomized trial to assess minimum duration of bisphosphonate after short-term denosumab and may be helpful to guide clinical care. Similar studies performed after longer durations of denosumab would be helpful to further define optimal management.

Trial registration: ClinicalTrials.gov registration number: NCT03623633.