Impact of noncompliance with alendronate and risedronate on the incidence of nonvertebral osteoporotic fractures in elderly women

AIMS To evaluate the association between noncompliance with alendronate and risedronate and the risk of nonvertebral osteoporotic fracture in community-dwelling elderly women. METHODS A nested case-control study was conducted using the Quebec administrative health databases. To be included in the cohort, women needed to be aged >= 68 years and to have initiated treatment with alendronate or risedronate between 1 January 2002 and 31 March 2005. Cases consisted of all women with an incident nonvertebral osteoporotic fracture occurring >= 1 year after initiation of therapy. Each case was matched with up to 20 controls using incidence density sampling, according to age (+/- 1 year) and follow-up duration. A woman was noncompliant if she had a medication possession ratio (MPR) < 80% for total follow-up duration. Rate ratios (RR) for fracture were estimated through conditional logistic regression analysis, adjusting for potential confounders. RESULTS Among the 30 259 women included in the cohort, 1036 nonvertebral fracture cases were identified and were matched to 20 069 controls. Compared with women with a MPR >= 80%, those with a MPR < 80% had a greater risk of nonvertebral fracture [adjusted RR 1.27, 95% confidence interval (CI) 1.12, 1.44]. Considering hip fracture only, the multivariate model yielded similar results, (adjusted RR 1.28, 95% CI 1.02, 1.61). CONCLUSIONS Among community-dwelling elderly women, noncompliance with alendronate or risedronate is associated with an increased risk of nonvertebral fracture.