Development of an economic model to assess the cost effectiveness of treatment interventions for chronic obstructive pulmonary disease

Objective: To develop a Markov model that allows the cost effectiveness of interventions in patients with chronic obstructive pulmonary disease (COPD) to be estimated, and to apply the model to investigate the cost effectiveness of an inhaled corticosteroid/long-acting β 2 -adrenoceptor agonist (β 2 -agonist) combination (salmeterol/fluticasone propionate) versus usual care. Methods: A Markov model consisting of four mutually exclusive disease states was constructed (mild, moderate and severe disease, and death). The transition probabilities of disease progression (for smokers and ex-smokers) and death were derived from the published medical literature. The model outputs were costs, exacerbations, survival, QALYs and cost effectiveness. The model was made fully probabilistic to reflect the joint uncertainty in the model parameters. Efficacy data for the combination of inhaled salmeterol/fluticasone propionate 50/500µg twice daily in poorly reversible COPD patients with a history of exacerbations were obtained from the 1-year TRISTAN (TRial of Inhaled STeroids ANd long-acting β-agonists) study and applied to the model, based on patient profiles representative of COPD clinical trials. Results: According to the model, the mean life expectancy with usual care alone (placebo group) was 8.95 years, which decreased to 4.08 QALYs once adjusted for quality and discounted, at a lifetime discounted cost of $Can16 415 per patient (year 2002 values). Assuming that salmeterol/fluticasone propionate reduced exacerbation frequency only (base case analysis), the estimated mean survival time remained unchanged but there was an increase in the number of QALYs (4.21) for an estimated lifetime cost of $Can25 780, resulting in a cost-effectiveness ratio of $Can74 887 per QALY (95% CI 21 985, 128 671) versus usual care. If a survival benefit was assumed for salmeterol/fluticasone propionate, the incremental cost per QALY was $Can11 125 (95% CI 8710, dominated) versus usual care. If the combination achieved around a 10% improvement in forced expiratory volume in 1 second, leading to delayed progression to more severe disease states, the benefits translated into an incremental cost per QALY of $Can49 928 (95% CI 37 269, 66 006) versus usual care. Conclusions: This Markov model allows, for the first time, a means of estimating the long-term cost effectiveness and cost utility of interventions for COPD. Initial evidence suggests that for patients with poorly reversible COPD and a documented history of frequent COPD exacerbations, the addition of salmeterol (a longacting β 2 -agonist) to fluticasone propionate (an inhaled corticosteroid) is potentially cost effective from the Canadian healthcare payer’s perspective. However, the precision of this estimate will be improved when additional data are available from clinical trials such as the ongoing TORCH (TOwards a Revolution in COPD Health) study. Copyright Adis Data Information BV 2005