title: Is polypharmacy always hazardous? A retrospective cohort analysis using linked electronic health records from primary and secondary care.
abstract: OBJECTIVE
  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.
authors.affiliation: Cambridge Centre for Health Services Research, Institute of Public Health, University of Cambridge, Cambridge, CB2 0SR, UK.
authors.forename: Rupert A
authors.initials: RA
authors.lastname: Payne
authors.forename: Gary A
authors.initials: GA
authors.lastname: Abel
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Avery
authors.forename: Stewart W
authors.initials: SW
authors.lastname: Mercer
authors.forename: Martin O
authors.initials: MO
authors.lastname: Roland
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D057286:Electronic Health Records; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D019338:Polypharmacy; D011320:Primary Health Care; D012189:Retrospective Studies; D063127:Secondary Health Care
keywords: hospital admission; multimorbidity; polypharmacy; primary care