PATTERNS OF USE AND COMPARATIVE SAFETY OF NEW AND OLD ANTICHOLINERGIC MEDICATIONS IN OLDER ADULTS: A POPULATION-BASED STUDY
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Overactive bladder (OAB) and urge urinary incontinence (UUI) are conditions that affect 12 – 18% of Canadians and that grow increasingly common with age. Patterns of use and comparative safety of six anticholinergic medications used to treat OAB and UUI were examined. Two of these medications (oxybutynin, tolterodine) have been included for many years on the provincial drug formulary, while the other four (solifenacin, darifenacin, trospium chloride, fesoterodine) have only recently been listed with conditions as “limited use” (LU) products. Acute urinary retention is a possible adverse outcome associated with these medications and was the outcome selected for the analysis of comparative safety. Participants were patients from Ontario between 66 and 105 years of age who received a new prescription for one of the bladder anticholinergic medications listed on the formulary between December 15, 2011 and December 31, 2013. A retrospective cohort design was used. Patients who were new users of any of the six bladder anticholinergic medications were identified from ODB program data. Descriptive statistics were used to assess physician adherence to the LU criteria. These patients were assigned to groups based on the bladder anticholinergic medication they received and the risk of acute urinary retention in new users of each medication was compared. Cox Proportional Hazards models were used to calculate hazard ratios to compare the risk of acute urinary retention among new users of each of the newer medications as compared to new users of oxybutynin. Analyses were stratified by sex, as men are known to be at greater risk of urinary retention than women. Only 10% of patients met the LU criteria for a prior trial of oxybutynin. Among men (but not women), new use of solifenacin, darifenacin, or tolterodine was associated with a reduced risk of acute urinary retention as compared to oxybutynin. The LU criteria for newer bladder anticholinergic medications do not appear to serve as an effective means of regulating their prescription. Exposure to these medications appears to confer a lower risk of acute urinary retention than oxybutynin in male patients. Further research into other potential adverse effects of these medication is needed.