The Association Between Drug Burden Index (DBI) and Health-Related Outcomes: A Longitudinal Study of the 'Oldest Old' (LiLACS NZ)

Background The prescribing of medications with anticholinergic and/or sedative properties is considered potentially inappropriate in older people (due to their side-effect profile), and the Drug Burden Index (DBI) is an evidence-based tool which measures exposure to these medications. Life and Living in Advanced Age: a Cohort Study in New Zealand (LiLACS NZ) is an ongoing longitudinal study investigating the determinants of healthy ageing. Using data from LiLACS NZ, this study aimed to determine whether a higher DBI was associated with poorer outcomes (hospitalisation, falls, mortality and cognitive function and functional status) over 36 months follow-up. Methods LiLACS NZ consists of two cohorts: Maori (the indigenous population of New Zealand) aged >= 80 years and non-Maori aged 85 years at the time of enrolment. Data relating to regularly prescribed medications at baseline, 12 months and 24 months were used in this study. Medications with anticholinergic and/or sedative properties (i.e. medications with a DBI > 0) were identified using the Monthly Index of Medical Specialities (MIMS) medication formulary, New Zealand. DBI was calculated for everyone enrolled at each time point. The association between DBI at baseline and outcomes was evaluated throughout a series of 12-month follow-ups using negative binomial (hospitalisations and falls), Cox (mortality) and linear (cognitive function and functional status) regression analyses (significance p < 0.05). Regression models were adjusted for age, gender, general practitioner (GP) visits, socioeconomic deprivation, number of medicines prescribed and one of the following: prior hospitalisation, history of falls, baseline cognitive function [Modified Mini-Mental State Examination (3MS)] or baseline functional status [Nottingham Extended Activities of Daily Living (NEADL)]. Results Full demographic data were obtained for 671, 510 and 403 individuals at baseline, 12 months and 24 months, respectively. Overall, 31%, 30% and 34% of individuals were prescribed a medication with a DBI > 0 at baseline, 12 months and 24 months, respectively. At baseline and 12 months, non-Maori had a greater mean DBI (0.28 +/- 0.5 and 0.27 +/- 0.5, respectively) compared to Maori (0.16 +/- 0.3 and 0.18 +/- 0.5, respectively). At baseline, the most commonly prescribed medicines with a DBI > 0 were zopiclone, doxazosin, amitriptyline and codeine. In Maori, a higher DBI was significantly associated with a greater risk of mortality: at 36 months follow-up, adjusted hazard ratio [95% confidence interval (CI)] 1.89 (1.11-3.20), p = 0.02. In non-Maori, a higher DBI was significantly associated with a greater risk of mortality [at 12 months follow-up, adjusted hazard ratio (95% CIs) 2.26 (1.09-4.70), p = 0.03] and impaired cognitive function [at 24 months follow-up, adjusted mean difference in 3MS score (95% CIs) 0.89 (- 3.89 to - 0.41), p = 0.02). Conclusions Using data from LiLACS NZ, a higher DBI was significantly associated with a greater risk of mortality (in Maori and non-Maori) and impaired cognitive function (in non-Maori). This highlights the importance of employing strategies to manage the prescribing of medications with a DBI > 0 in older adults.