Introducing a methodology to use activities of daily living outcomes in the assessment of the cost-effectiveness of AD treatments: a case study using rivastigmine patch

Objective: Measures of activities of daily living (ADL), as a functional assessment, may be a more accurate payer-relevant reflection of disease burden than cognitive assessments in Alzheimer's disease. The objective of this study is to evaluate the usefulness of ADL instruments in cost-effectiveness modelling in Alzheimer's disease.

Methods: A core economic model used Mini Mental State Examination (MMSE) scores from the IDEAL trial, which demonstrated significant benefits for rivastigmine patch over placebo. The model was adapted to include Alzheimer's Disease Cooperative Study Activities of Daily Living Inventory (ADCS-ADL) scores, with assumptions made on disease progression over a 5-year period. The clinical pathway was populated based on the results of the pivotal IDEAL trial, with 12-month follow-up data from patients who received rivastigmine patch (n=383) and 6-month follow-up data from patients who received placebo (n=282). The progression of the disease was modelled beyond the study period of one year by defining ADCS-ADL as a function of MMSE, and using published equations on disease progression to predict the natural decline of MMSE. The ADCS-ADL data were then mapped to the Townsend Activities of Daily Living (Townsend-ADL) scale for the prediction of institutionalization. Costing variables included drugs, clinical monitoring, institutionalization and community burden of care.

Results: The model based on MMSE scores showed an incremental cost per quality adjusted life year (QALY) gained over best supportive care (BSC) of £13,042, whereas the Townsend-ADL model indicated total cost savings, primarily attributable to number of institutionalized days avoided over 5 years (67.5 days for ADL compared to 19.2 days for MMSE). Results were insensitive to the type of regression analyses (linear versus logistic) that were carried out to establish the relationship of MMSE and ADL scales.

Conclusions: Both the MMSE and Townsend-ADL models demonstrated the cost-effectiveness of rivastigmine patch for patients with AD. ADL modeling should be regarded as a valuable technique for future economic evaluations in the treatment of AD.