Polypharmacy and injurious falls in older adults: a nationwide nested case-control study

OBJECTIVE: To determine whether or not the exposure to multiple drugs (polypharmacy) increases the risk of fall-related injury among older adults, beyond the effect of fall-risk increasing drugs and chronic multimorbidity. METHODS: Nested case-control study using linked register data with national coverage in Sweden. We defined cases as older adults (≥70 years) who had an incident non-elective admission due to a fall between 1 January and 31 December 2013. Cases were matched 1:1 on sex, age and index date to randomly selected controls from the general population. The number of prescription drugs during the 7 days preceding the index date was the main exposure. RESULTS: A total of 49,609 cases were included and matched to an equal number of controls. The number of prescription drugs was higher among cases than among controls (mean difference 1.2, 95% CI 1.16–1.26). While adjusting for potential confounders, we found that the risk of injurious falls increased in a nearly linear fashion for each additional drug (OR, 1.02; 95% CI, 1.01–1.03). When using a cut-off value of ≥4 drugs to define polypharmacy, the population attributable fraction for injurious falls was 5.2% (95% CI 2.8–7.6). CONCLUSION: This study shows a monotonic dose-response relationship between the number of drugs and the risk of injurious falls. However, after comprehensive adjustment for known confounders (including fall-risk increasing drugs and chronic multimorbidity), this association is substantially weaker than previously reported. Moreover, even if the relationship between polypharmacy and injurious falls is really causal, the population attributable risk fraction is low.