Drug class duplication patterns among South African middle-aged adults: findings from a medicine claims database

Middle-aged adults (45-64 years), who constitute a large proportion of the population, are at risk of potentially inappropriate medicine (PIM) prescribing due to their high prevalence of multimorbidity. Drug class duplication, the concurrent prescription of two or more medicines from the same pharmacological class, is a commonly reported PIM criterion in studies using the PRescribing Optimally in Middle-aged People's Treatments (PROMPT) criteria.

To determine the prevalence of drug class duplication, stratified by sex and age group, and its associated factors among middle-aged adults using a South African pharmaceutical benefit management (PBM) company's medicine claims database.

A cross-sectional study was conducted using data from 1 January 2023-31 December 2023. Drug class duplication was assessed across 14 pharmacological drug classes. Prevalence of drug class duplications was analysed by sex and age group, with associations tested using Pearson's chi-square test. Spearman's correlation coefficient (r_s) was used to assess the correlation between drug class duplication and potential associated factors.

Of the 195,446 patients analysed (51.9% female; mean age 53.69 years [standard deviation (SD) 5.41, 95% confidence interval (CI) 53.665-53.713]), 48.8% experienced one or more drug class duplication. Duplication was similar between sexes (p = 0.1685) and higher in older age groups (p < 0.0001, Cramér's V = 0.2). The most prevalent drug class duplications were 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) (n = 36,887, 18.9%); non-steroidal anti-inflammatory drugs (NSAIDs) (n = 30,829, 15.8%); angiotensin-converting enzyme (ACE) inhibitors (n = 25,646, 13.1%); angiotensin II receptor blockers (ARBs) (n = 22,411, 11.5%); calcium-channel blockers (CCBs) (n = 15,716, 8.0%); selective serotonin reuptake inhibitors (SSRIs) (n = 12,139, 6.2%); and beta-receptor blockers (β-blockers) (n = 11,577, 5.9%). Strong correlations were observed between drug class duplication and the number of Chronic Disease List (CDL) conditions per patient (r_s = 0.680, 95% CI 0.678-0.683), and number of prescriptions per patient (r_s = 0.638, 95% CI 0.636-0.641). Correlation with the number of medicine items per prescription per patient was moderate (r_s = 0.391, 95% CI 0.388-0.400), and weak with age (r_s = 0.232, 95% CI 0.227-0.236) (all p < 0.0001).

Drug class duplication was common, highlighting that targeted interventions may be useful to improve patient safety.