Comparative risk of delirium associated with oxybutynin and solifenacin in older adults

Te-yuan Chyou, Prasad Nishtala

Research output: Contribution to conferenceAbstractpeer-review


Title: Comparative risk of delirium associated with oxybutynin and solifenacin in older adults

Te-yuan Chyou, PhD1; Prasad S Nishtala, PhD2; 1Department of Biochemistry, University of Otago, Dunedin, New Zealand. 2Department of Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom;

Background: Antimuscarinics are indicated for the treatment of overactive bladder. One of the most debilitating central anticholinergic adverse effects of antimuscarinics in older adults is drug-induced delirium. In New Zealand (NZ), oral formulations of oxybutynin and solifenacin are the most frequently used antimuscarinics. Clinical trials provide limited information on the comparative risk of delirium between the two drugs.

Objective: This study's primary objective was to compare the risk of incident delirium in new users of oxybutynin and solifenacin aged 65 years or older. In the secondary analyses, we compared the adherence to the two antimuscarinics.

Method: We used the NZ national minimum data set and the pharmaceutical collections to identify older adults diagnosed with delirium and started oxybutynin or solifenacin between 01/01/2005 and 31/12/2016.. These two antimuscarinics are subsidised by the Pharmaceutical Management Agency and are the most frequently used antimuscarinic in NZ. We used dispensing claims data to determine antimuscarinic treatment exposure. The day the individual received the first prescription of oxybutynin or solifenacin is the index date. To compare the risk of incident risk, we followed each individual until the first delirium event after the index date and censored at discontinuation, drug switching or the cohort end. We followed each individual until the first discontinuation or drug switching and censored at delirium event or the cohort end to compare the adherence. The Cox proportional hazard (COXPH) regression model was used with inverse probability treatment weighting (IPTW) to evaluate delirium's comparative risk and adherence.

Results: We identified 4818 individuals (mean age 82.14) from 2005 to 2015 with incident delirium and exposed to at least one of the antimuscarinic of interest. After IPTW adjustment for confounders including comorbidity, COXPH regression showed that compared to solifenacin, the use of oxybutynin was associated with a greater risk of delirium (IPTW-adjusted hazard ratio (IPTW-HR) 2.06 (1.06-2.60)). However, there is no evidence that oxybutynin was less likely to be adhered to than solifenacin (IPTW-HR 0.85 (0.71 to 1.00)).

Conclusion: The study found that solifenacin is associated with a relatively lower risk of delirium than oxybutynin in older adults, but solifenacin had not been used preferentially. Prescribers should exercise caution when using oxybutynin in older adults who are at risk of or have cognitive impairment.
Original languageEnglish
Number of pages1
Publication statusPublished - 1 Aug 2021
Event37th ICPE, Seattle, USA - Virtual
Duration: 23 Aug 202125 Sept 2021


Conference37th ICPE, Seattle, USA
Internet address


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