Incorporating adherence into health economic modelling of osteoporosis
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Osteoporosis medications are seldom taken according to the recommendations of health-care providers. A theoretical model was constructed to investigate the variables of drug adherence that affect the cost-effectiveness of drugs, using osteoporosis treatment as a model. Important variables were the magnitude of drug effect, drug price, and fracture-related costs.
Adherence to anti-fracture medication is far from optimal and poses a challenge in osteoporosis management. The objectives of this study were to develop a model that could address adherence and identify the important drivers of cost-effectiveness.
An individual state transition model was constructed to compare two theoretical medications, one of which conferred optimal adherence and was 50% more costly. Adherence was divided into persistence and compliance. Partial compliance was assumed to be associated with a 20% loss of anti-fracture effect. Non-persistent patients had an offset time as long as their time on medication, to a maximum of 5 years.
The potentially important drivers of cost-effectiveness include reduced drug effectiveness due to poor compliance, offset time, fracture risk, anti-fracture drug effect, and drug price. Optimal adherence was associated with fewer osteoporotic fractures, and the impact was more evident among those with prior fractures. However, the health benefits of adherence were often partially offset by increased intervention costs associated with the improved drug-taking behaviour.
High adherence is likely to be associated with added value for health-care systems, but should be used with care as a central health economic argument.