Is polypharmacy always hazardous? A retrospective cohort analysis using linked electronic health records from primary and secondary care

Abstract

Aims: Prescribing multiple medications is associated with various adverse outcomes, and polypharmacy is commonly considered suggestive of poor prescribing. Polypharmacy might thus be associated with unplanned hospitalization. We sought to test this assumption.

Methods: Scottish primary care data for 180 815 adults with long-term clinical conditions and numbers of regular medications were linked to national hospital admissions data for the following year. Using logistic regression (age, gender and deprivation adjusted), we modelled the association of prescribing with unplanned admission for patients with different numbers of long-term conditions.

Results: Admissions were more common in patients on multiple medications, but admission risk varied with the number of conditions. For patients with one condition, the odds ratio for unplanned admission for four to six medications was 1.25 (95% confidence interval 1.11-1.42) vs. one to three medications, and 3.42 (95% confidence interval 2.72-4.28) for ≥10 medications vs. one to three medications. However, this effect was greatly reduced for patients with multiple conditions; amongst patients with six or more conditions, those on four to six medications were no more likely to have unplanned admissions than those taking one to three medications (odds ratio 1.00; 95% confidence interval 0.88-1.14), and those taking ≥10 medications had a modestly increased risk of admission (odds ratio 1.50; 95% confidence interval 1.31-1.71).

Conclusions: Unplanned hospitalization is strongly associated with the number of regular medications. However, the effect is reduced in patients with multiple conditions, in whom only the most extreme levels of polypharmacy are associated with increased admissions. Assumptions that polypharmacy is always hazardous and represents poor care should be tempered by clinical assessment of the conditions for which those drugs are being prescribed.

Keywords: hospital admission; multimorbidity; polypharmacy; primary care.

Figure 1

Adjusted odds ratios showing the association between admission and number of regular medications (relative to 1–3 regular medications), for different degrees of multimorbidity. For each number of clinical conditions, the clusters represent different numbers of medications, from none (white), through one to three, four to six, seven to nine, and 10 or more medications (black). Error bars are 95% confidence intervals. The point estimates shown in the figure can be calculated from the adjusted odds ratios reported in Appendix 2