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

Figures & data

Table 1 Characteristics of the study population

	Cases (N=49,609)	Controls (N=49,609)
Sex, No. (%)
Men	15,285 (30.8)	15,285 (30.8)
Women	34,324 (69.2)	34,324 (69.2)
Age, years
Mean (SD)	83.2 (7.2)	83.7 (7.2)
No. (%)
70–79 years	16,237 (32.7)	15,368 (31.0)
80–89 years	22,728 (45.8)	22,532 (45.4)
≥90 years	10,644 (21.5)	11,709 (23.6)
Living arrangement, No. (%)
Community	42,818 (86.3)	44,054 (88.8)
Nursing home	6,791 (13.7)	5,555 (11.2)
Marital status^a, No. (%)
Single	3,463 (7.0)	2,924 (6.2)
Married	15,791 (31.9)	17,276 (36.4)
Divorced	7,377 (14.9)	5,843 (12.3)
Widowed	22,848 (46.2)	21,361 (45.1)
Level of education^b, No. (%)
Primary education	22,057 (45.4)	21,676 (45.1)
Secondary education	19,443 (40.0)	19,013 (39.6)
Tertiary education	7,103 (14.6)	7,375 (15.3)
Fall-risk increasing drugs
Mean (SD)	2.5 (2.0)	2.0 (1.7)
No. (%)
0	8,488 (17.1)	11,565 (23.3)
1	8,799 (17.7)	9,935 (20.0)
≥2	32,322 (65.2)	28,109 (56.7)
Number of chronic diseases
Mean (SD)	4.9 (3.4)	3.8 (3.0)
No. (%)
0	3,167 (6.4)	5,344 (10.8)
1	4,623 (9.3)	6,822 (13.8)
2	5,609 (11.3)	7,252 (14.6)
≥3	36,210 (73.0)	30,191 (60.9)
History of fall-related hospitalisation, No. (%)
Yes	13,134 (26.5)	7,649 (15.4)
No	36,475 (73.5)	41,960 (84.6)
History of alcohol-related hospitalisation, No. (%)
Yes	1,003 (2.0)	259 (0.5)
No	48,606 (98.0)	49,350 (99.5)
Drug dispensing scheme
Ordinary prescriptions	36,270 (73.1)	40,818 (82.3)
Multidose dispensing	13,339 (26.9)	8,791 (17.7)

Notes: ^aMissing values for marital status: 130 (0.3%) for cases and 2205 (4.4%) for controls. ^bMissing values for the level of education: 1006 (2.0%) for cases and 1545 (3.1%) for controls

Figure 1 Dose-response relationship between the number of prescription drugs and the risk of injurious fall.

Notes: Odds ratios for fall-related hospital admissions modelled by restricted cubic spline models. The number of prescription drugs was transformed using restricted cubic regression splines with knots at 3, 5, 8 and 13 drugs. Conditional logistic regression models were then fitted to estimate odds ratio (solid curves) with pointwise 95% confidence intervals (dashed curves). The median number of drugs (5) was chosen as reference point. The fully adjusted model was matched on sex, age and index date, and further adjusted for the number of fall-risk increasing drugs (FRIDs), living arrangement, number of chronic diseases, history of fall-related hospital admission, and history of alcohol-related hospital admission. Assuming linearity, an odds ratio of 1.02 (95% CI 1.01–1.03) was observed for every increase of 1 drug during the 7-day period before (but not including) the index date.
Abbreviation: FRID, fall-risk increasing drug.

Table 2 Association between the number of prescription drugs and risk of injurious fall

	Cases (n=49,609)	Controls (n=49,609)	Matched^a	Matched and adjusted for FRID use^b	Matched and adjusted for multiple confounders^c
			OR (95% CI)	OR (95% CI)	OR (95% CI)
Number of drugs ^d
Mean (SD) N (%)	6.4 (4.2)	5.2 (3.8)	1.08 (1.07–1.09)	1.07 (1.06–1.07)	1.02 (1.01–1.03)
0 to 3 drugs	13,246 (26.7)	18,111 (36.5)	1	1	1
4 to 6 drugs	13,896 (28.0)	14,961 (30.2)	1.29 (1.25–1.33)	1.22 (1.17–1.26)	1.06 (1.02–1.10)
7 to 9 drugs	11,599 (23.4)	9,918 (20.0)	1.64 (1.58–1.7)	1.48 (1.42–1.55)	1.13 (1.08–1.19)
10 to 14 drugs	8,722 (17.6)	5,734 (11.6)	2.13 (2.05–2.22)	1.83 (1.73–1.93)	1.21 (1.13–1.28)
≥15 drugs	2,146 (4.3)	885 (1.8)	3.35 (3.09–3.64)	2.68 (2.43–2.96)	1.47 (1.32–1.64)

Notes: ^aConditional logistic regression model matched on sex and age. ^bConditional logistic regression model matched on sex and age, and further adjusted for the number of fall-risk increasing drugs. ^cConditional logistic regression model matched on sex and age, and further adjusted for the number of fall-risk increasing drugs, living arrangement, number of chronic diseases, history of fall-related hospital admission, and history of alcohol-related hospital admission. ^dDrug exposure period: 7 days preceding (but not including) the index date.

Abbreviations: OR, odds ratio; CI, confidence interval; FRID, fall-risk increasing drugs.

Figure 2 Population attributable fraction (PAF). ^aOdds Ratios and their 95% confidence intervals were computed by the mean of unconditional logistic regression models adjusted for sex, age, number of fall-risk increasing drugs (FRIDs), living arrangement, number of chronic diseases, history of fall-related hospital admission, and history of alcohol-related hospital admission. ^bThe population attributable fraction (PAF) can be calculated as PAF = Pe × [(OR-1) ÷ OR], where Pe is the prevalence rate of the exposure among cases.

Availability of data and materials

Patient-level data from the Swedish Prescribed Drugs Register and other healthcare registers cannot be made publicly available. Interested researchers can access the aggregated data from the Swedish Prescribed Drugs Register (www.socialstyrelsen.se/statistik/statistikdatabas/lakemedel). Additional data can be obtained upon reasonable request to the authors.