Clinical and Demographic Factors Associated with Antimuscarinic Medication Use in Older Hospitalized Patients

Background: Antimuscarinic drug prescribing scoring systems might better identify patients at risk of adverse drug reactions. The recently developed Anticholinergic Risk Scale (ARS) score is significantly associated with the number of antimuscarinic side effects in older outpatients. We sought to identify the clinical and demographic patient-level correlates of the ARS, including a modified version adjusted for daily dose, in elderly hospitalized patients. Methods: Clinical and demographic patient characteristics known to be associated with antimuscarinic prescribing, ARS and dose-adjusted ARS scores, and full medication exposure on admission were recorded in 362 consecutive patients (aged 83.6 ± 6.6 years) admitted to 2 geriatric units (NHS Grampian, Aberdeen, Scotland, UK) between February 1, 2010 and June 30, 2010. Results: Each year of increasing age was associated with reduced number of antimuscarinic drugs (incidence rate ratio [IRR], 0.963; 95% confidence interval [CI], 0.948–0.980; P < 0.001), non-antimuscarinic drugs (IRR, 0.991; 95% CI, 0.985–0.997; P = 0.006), and total number of drugs (IRR, 0.988; 95% CI, 0.983–0.994; P < 0.001). Multivariate Poisson regression showed that increasing age and history of dementia were negatively associated with the ARS score (IRR, 0.97; 95% CI, 0.94–0.99; P = 0.001 and IRR, 0.62; 95% CI, 0.41–0.92; P = 0.019, respectively). By contrast, institutionalization (IRR, 1.32; 95% CI, 1.00–1.74; P = 0.050), Charlson comorbidity index (IRR, 1.06; 95% CI, 1.01–1.11; P = 0.015), and total number of non-antimuscarinic drugs (IRR, 1.13; 95% CI, 1.08–1.18; P < 0.001) were all positively associated with the ARS score. Similar results were observed for the dose-adjusted ARS score. Conclusion: Institutionalization, comorbidities, and non-antimuscarinic polypharmacy show independent positive associations with the ARS and dose-adjusted ARS scores in older hospitalized patients. Increasing age and dementia are negatively associated with the ARS score.