Incidence of Venous Thromboembolism in Users of Strontium Ranelate
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Background: Strontium ranelate is indicated for the treatment of postmeno-pausal osteoporosis. An association between strontium ranelate and venous thromboembolism (VTE) was identified in an analysis of phase III clinical trials.
Objective: To estimate the incidence of VTE in patients within the strontium ranelate (Protelos®) Prescription-Event Monitoring (PEM) study cohort during the first 12 months after starting treatment.
Methods: Patients in this analysis were identified from dispensed prescriptions that had been issued by general practitioners (GPs) in England for strontium ranelate between October 2004 and January 2008. For each individual patient, a Green Form questionnaire was sent to their GP 12 months after the date of the first prescription issued for strontium ranelate, requesting information about the patient including start and stop dates of treatment (if stopped), age, sex, indication, any history of VTE events, reasons for stopping and whether the patient had any events since starting the drug. VTE was defined as reports of deep vein thrombosis (DVT) or pulmonary embolism (PE). The crude incidence of VTE was calculated for events that occurred during the first 12 months after starting treatment (plus 30 days after stopping), with 95% Poisson exact CIs for the whole cohort, and subsets defined by age and past history of VTE.
Results: The final analysis cohort consisted of 10 782 patients. Where specified, mean age was 73.3 years (SD 11.45) [n= 10 696]; 9833 (91.3%) were female and 934 (8.7%) were male. Where the history of VTE was specified, 233 patients (2.6%) had a history of VTE prior to starting. In the first 12-month period, there were 48 incident reports of VTE (DVT or PE) during treatment (or within 30 days of stopping) in the cohort, with 7696.89 years of exposure, giving a crude incidence rate of VTE of 6.24 cases (95% CI 4.60, 8.27) per 1000 patient-years exposed.
Conclusions: This analysis has provided an estimate of the incidence of VTE in patients treated with strontium ranelate in the general practice setting. The rate is similar to estimates in populations of similar age and corresponds to the incidence found in patients from phase III clinical studies and observational cohort studies of strontium ranelate on this topic. The crude annual incidence rate of VTE in the PEM cohort is higher than the background annual incidence rate found in the UK population, but is similar to estimates in populations of similar age and populations receiving treatment for post-menopausal osteoporosis. Also, we acknowledge the potential for underestimating the incidence in this population. Nevertheless, this analysis contributes to the ongoing postmarketing safety assessment of this product.
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