Baseline β-CTX and BMI predict suitability for deferred zoledronic acid redosing beyond 12 months in postmenopausal Indian women with osteoporosis.

PURPOSE: To evaluate whether baseline bone turnover markers (BTMs), particularly plasma β-C-terminal telopeptide of type I collagen (β-CTX), and body mass index (BMI) predict the feasibility and short-term safety of deferring zoledronic acid redosing beyond 12 months in postmenopausal Indian women with osteoporosis.

METHODS

In this prospective observational study, 50 treatment-naïve postmenopausal women with DXA-confirmed osteoporosis received intravenous zoledronic acid (5 mg). At the 12-month visit, β-CTX guided repeat dosing: women with β-CTX ≥300 pg/mL were redosed, whereas those with β-CTX <300 pg/mL underwent 12-weekly biochemical surveillance, with redosing deferred until β-CTX recovery or a maximum of 24 months. Multivariable logistic regression identified baseline predictors of delayed redosing (>12 months).

RESULTS

Twenty-five women underwent delayed redosing (median interval 18.5 months). Compared with standard dosing, the delayed group had lower baseline β-CTX (582 vs 866 pg/mL; p < 0.001) and lower BMI (23.4 ± 5.5 vs 25.7 ± 2.0 kg/m2; p = 0.008). On multivariable analysis, lower baseline β-CTX (adjusted OR per 100 pg/mL 0.48; 95% CI 0.31-0.73; p = 0.001) and lower BMI (adjusted OR per kg/m2 0.81; 95% CI 0.67-0.98; p = 0.031) independently predicted delayed redosing. BMD gains were comparable between groups and no new vertebral fractures occurred during 2-year follow-up.

CONCLUSION

Lower baseline bone turnover and lower BMI were associated with delayed zoledronic acid redosing, supporting a biomarker-guided approach to individualized treatment intervals.