Cost–utility analysis of an intervention designed to reduce the critical handling error of insufficient inspiratory effort

Objectives Up to 70–80% of patients use inhalers incorrectly. Dry-powder inhalers (DPIs) require forceful inhalation for optimal delivery, and approximately 40% of Global Initiative for Asthma (GINA)-defined Step-3+ patients inhale corticosteroid and long-acting beta-agonist through DPIs. The CRITIKAL study (Price et al. in J Allergy Clin Immunol Pract 5:1071-e9–1081-e9, 2017) found a statistically significant association between ‘insufficient inspiratory effort’ error and increased risk of uncontrolled asthma and hospitalisation-requiring exacerbations. This paper explores the cost-effectiveness of an error-targeted intervention. Methods A probabilistic Markov cost–utility model simulated patients transitioning between controlled and uncontrolled health states over one year. Odds ratios (ORs, from the CRITIKAL study) of a patient having uncontrolled asthma conditional on making the error were applied to baseline transition probabilities sourced from the literature, both indirectly via an adjustment formula (Zhang et al. in JAMA 280:1690–1691, 1998) and directly by assuming OR approximates relative risk (RR). The analysis explored complete/partial eradication of the error when the intervention was priced to match comparators, as well as impact of indirect costs based on lost/reduced productivity. Results The intervention dominated both DPI comparators over one year, with direct cost savings of £45/£86 with 0.0053/0.0102 additional quality-adjusted life years (QALYs), and had the highest probability of being cost-effective at a £20,000/QALY threshold. Key factors driving variance were weekly utilities per state and RR of moving to an uncontrolled state. Conclusion The analysis demonstrated the economic and societal costs of ‘insufficient inspiratory effort’ and potential economic benefits of introducing an effective intervention to reduce/eradicate this error. Further research should assess the economic impact of other handling errors.