Defining polypharmacy in older adults: a cross-sectional comparison of prevalence estimates calculated according to active ingredient and unique product counts

Abstract Background Polypharmacy is common in older adults and may be associated with poor outcomes. However, methods used to define polypharmacy are rarely reported precisely, with potential implications for polypharmacy exposure estimates. Aim The aim was to investigate prevalence estimates according to different methods in an Australian population-based sample of older adults. Method This cross-sectional study included 735 adults aged ≥ 60 years participating in the Geelong Osteoporosis Study. Current prescription, non-prescription and complementary and alternative medicines were self-reported. Counting methods included the number of active ingredients and unique products. Polypharmacy and hyperpolypharmacy were determined using ≥ 5 and ≥ 10 medicine cut points respectively. Prevalence was estimated using ingredient- and product-level counts according to criteria defined by medicine schedule and type (i.e. scheduled prescription, non-prescription). Non-parametric testing measured differences between counting methods, univariate logistic regressions investigated disagreement between total counts and polypharmacy exposure. Results Polypharmacy prevalence (scheduled prescription medicines) was 30.3% and 35.9% (products versus ingredients). Prevalence increased to 52.8% and 57.3% when counts considered any medicine. Adults aged ≥ 80 years were most likely to use prescription combination products (OR 2.22 [95% CI 1.46, 3.35] p < 0.01), however, age was not associated with disagreement between product and ingredient polypharmacy exposure. Being male was associated with both prescription combination product use (OR 1.79 [95% CI 1.29, 2.47] p < 0.001) and disagreement between polypharmacy exposures (OR 2.29 [95% CI 1.15, 4.47] p=0.02). Conclusion Polypharmacy prevalence estimates varied substantially depending on the method applied. These data indicate the need for standardised reporting specific to medicines data and polypharmacy measures.