Purpose:​ Early initiation of anti-osteoporosis medications (AOMs) is recommended for patients on long-term glucocorticoid (GC) therapy. This study aimed to examine whether physicians prescribe AOMs as soon as GC therapy is initiated, and whether a delay in AOM initiation affects hip and vertebral fracture incidence, using the nationwide health insurance claims database of Japan (NDBJ).

Methods:​ Patients aged ≥50 years who were prescribed GC (≥5 mg/day prednisolone or equivalent) for ≥90 days and who were followed for AOM use and hip and vertebral fracture events for the subsequent 1080 days in 2012–2018 were selected from NDBJ. Delay in AOM initiation was defined as the number of days without AOMs following GC therapy initiation. Associations between delay in AOM initiation and hip and vertebral fracture risk were evaluated by Cox proportional hazards regression.

Results:​ In total, 92,143 women and 94,772 men were included in the analysis, of which only 39.3% of women and 28.5% of men received AOMs within 90 days from GC therapy initiation. Approximately, 15% of hip fractures and 30% of vertebral fractures occurred before AOM initiation in patients with delayed AOM initiation. HRs of both fractures were significantly greater in patients with a longer delay in AOM initiation (p value for trend<0.001). After excluding patients who had fractures before AOM initiation, the magnitude of HRs significantly decreased, and HR trends for hip fracture became insignificant.

Conclusions:​ Delayed initiation of AOMs may result in increased fracture events, which may be reduced by early initiation of AOMs.