Dementia and use of drugs : economic modelling and population-based studies

Abstract

The overall aim of this thesis was to investigate epidemiological and health economic aspects of dementia and drug use in older people, through economic modelling and analyses of population-based studies. The major findings from the separate studies are summarized below.

Study I We aimed to investigate whether dementia was associated with higher drug costs in 4,108 participants aged ≥ 60 years from the Swedish National Study on Aging and Care in Kungsholmen and Nordanstig (SNAC-K and SNAC-N). Overall, the average crude cost of drug use was 6,147 SEK per year for people with dementia and 3,810 SEK per year for people without dementia. The cost of nervous system drugs was more than five times higher in persons with dementia than without. However, the higher crude costs for drug use in people with dementia were confounded by comorbidities and residential setting. In fact, the strongest drug cost driver was comorbidity followed by residential setting.

Study II We aimed to investigate inappropriate drug use (IDU) and risk of hospitalizations and mortality in older persons and in persons with dementia and to also estimate the costs of IDU-related hospitalizations. In this study, based on data from SNAC-K and SNAC-N, the National Patient Register and the Cause of Death Register, we used logistic and Cox regression models to analyse associations between IDU, hospitalizations and mortality in the whole study population and in the subpopulation of persons with dementia. We found a higher risk of hospitalization (adjusted OR=1.46; 95% CI 1.18-1.81) and mortality (adjusted HR=1.15; 95% CI 1.01-1.31) in the whole study population and with hospitalization (adjusted OR=1.88; 95% CI 1.03-3.43) in the subpopulation of persons with dementia, after adjustment for confounding factors. There was also a tendency for higher costs for hospitalizations with IDU than without IDU, although not statistically significant.

Study III We aimed to describe the costs of an incident cohort of persons with dementia through simulation modelling. With input from epidemiological data, the Markov model estimated approximately 24,000 incident cases of dementia in Sweden in 2005. The incident cohort was run in the model for ten cycles of one year each. State specific costs were used and defined by the Clinical Dementia Rating scale. Results of the simulation showed that the total costs of the cohort were 27.7 billion SEK. The average annual cost of one person with dementia was 269,558 SEK. The severe state of dementia accounted for the largest proportion of costs for incident dementia cases. Costs of drugs in dementia only accounted for about 2% of the costs in the model. The main cost driver was institutional care, even for mild dementia.

Study IV We aimed to introduce a hypothetical economic model of a disease modifying treatment (DMT) for Alzheimer’s disease (AD). We created a Markov model built on Swedish conditions with two arms; one representing the hypothetical treatment and the other arm representing no treatment. States and progression of the disease were defined with Mini Mental State Examination. Epidemiological data of incidence, prevalence and costs of mild cognitive impairment (MCI), studies of conversion from MCI to AD and official statistics were used as input in the model. The incremental cost effectiveness ratio was 293,002 SEK/Quality Adjusted Life Year. The treated persons showed increased survival (8.7 years) versus the non-treated persons (7.8 years). With a societal willingness to pay of 600,000 SEK, the hypothetical treatment can be considered as cost effective. The main reasons for the higher costs with DMT were the costs of DMT itself and the prolonged survival with DMT.

Conclusion: The observed higher crude drug costs in dementia were confounded by comorbidities and residential setting. We also found that IDU was associated with an increased risk of hospitalization and mortality among older persons. This underlines the need for cautious prescribing to elderly patients. However, further studies are needed to investigate the association between IDU and costs for hospitalizations.

The highest accumulated costs in dementia occur in severe dementia and the major cost driver is institutionalization, even in mild dementia. Drugs, on the other hand, constitute only a minor part of the total costs. Our study of a hypothetical DMT showed that DMT in AD is projected as not being cost saving if the treatment prolongs survival. Still, if a societal willingness-to pay level of 600,000 SEK is adopted, the treatment can be considered as cost effective.