Comparison of existing polypharmacy measures to a measure incorporating all modes of administration: an observational...

Polypharmacy is often associated with adverse clinical outcomes and increased medication management complexity. However conventional analyses of medicine burden and polypharmacy using administrative data are limited to oral medicines (i.e. tablets and capsules), potentially underestimating overall medicine exposure. These products may significantly increase the burden of medication management and therefore risk to patients.

This study compared traditional measures of polypharmacy with a measure incorporating all modes of medicine administration and examined how these differences impacted estimates of polypharmacy prevalence among adults aged > 65 years in Western Australia (WA) from 2012/13 to 2018/19, between two independent cohorts: community-dwelling and residential aged care home populations.

Linked medication dispensing data were used to classify and compare medicines between community-dwelling and residential aged care populations in Western Australia. Conventional medicine capture was extended to include medicines via various modes of administration, including creams, ointments, patches, and eye and ear drops. Medicines were classified into five categories: 0, 1, 2-4, 5-8, 9 + medicines, and counts were compared across care settings to assess changes in observed medicine burden and measures of polypharmacy. Comparative analysis was performed between two methods: Method 1 (conventional medicine capture) and Method 2 (all medicines including non-oral preparations).

Inclusion of medicines via mode of administration increased observed medicine burden in both subpopulations, with a greater relative increase in residential aged care. This approach notably contributed to total medicine counts, revealing previously unrecognised medicine exposure. This resulted in absolute increases in the 5 + medicine category of 4.0% in 2012/13 and 3.4% in 2018/19. Among aged care residents, opioid analgesics previously ranked as the most common medicine class using Method 1, was reclassified as separate oral and patch formulations using Method 2, ranking 4th and 5th. Drugs for dry eyes also emerged as the 7th most common medicine class, with only minor ranking changes observed for the other top medicine classes.

Incorporating all modes of medicine administration into a polypharmacy measure substantially altered estimates of medicine burden and identified previously unrecognised exposure, particularly among residential aged care populations. The impact was greatest in higher polypharmacy categories, indicating that conventional approaches may underestimate medicine use in individuals with more complex therapeutic regimens. These findings highlight the importance of accounting for formulation diversity and support the inclusion of mode-of-administration-based measures to provide a more comprehensive assessment of medication exposure and complexity.