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

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.