Context: Studies having reported high rates of discontinuation of antiresorptive therapies (ART) may not reflect their actual use. Objectives: We compared probability of discontinuation among women aged 70 yr or older with a diagnosis of osteoporosis or recent osteoporotic fracture having started ART (alendronate, risedronate, cyclical etidronate, raloxifene, nasal calcitonin) between 1998-2001 or 2002-2004. Patients and Methods: We constructed two cohorts of women using Regie de l'Assurance Maladie du Quebec databases. Discontinuation was defined as a lapse of 30 d or longer after completion of a refill. Switching from one ART to another was allowed. Probability of discontinuation was estimated using Kaplan-Meier analysis. Multivariate Cox models were used to identify potential determinants of ART discontinuation over 1 yr. Results: After 1 yr, probability of discontinuation was slightly lower in the 2002-2004 cohort than the 1998-2001 cohort (52.2 vs. 57.5%; P < 0.001). This difference remained significant after adjusting for determinants [adjusted rate ratio (RR) 0.92, 95% confidence interval (CI) 0.87-0.98]. Significant determinants of ART discontinuation within 1 yr included bone mineral density testing (RR 0.77; CI 0.73-0.82) performed within 2 yr prior to initiation of therapy and having consulted more than two pharmacies (RR 1.15; CI 1.06-1.25) in the year before starting therapy. In the 2002-2004 cohort, when switching was allowed, women initiating a once-weekly regimen of alendronate or risedronate did not show a 1-yr risk of discontinuation different from women initiating daily regimens of the same drugs (RR 0.90; CI 0.82-1.00). Conclusions: Even if new dosing regimens were introduced, discontinuation of ART among osteoporotic women remains high.
