Asthma and lower airway disease
The prevalence of severe refractory asthma

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Background

Severe asthma is characterized by difficulty to achieve disease control despite high-intensity treatment. However, prevalence figures of severe asthma are lacking, whereas longstanding estimates vary between 5% and 10% of all asthmatic patients. Knowing the exact prevalence of severe refractory asthma as opposed to difficult-to-control asthma is important for clinical decision making, drug development, and reimbursement policies by health authorities.

Objective

We sought to estimate the prevalence of severe refractory asthma as defined by the Innovative Medicine Initiative consensus.

Methods

Adult patients with a prescription for high-intensity treatment (high-dose inhaled corticosteroids and long-acting β2-agonists or medium- to high-dose inhaled corticosteroids combined with oral corticosteroids and long-acting β2-agonists) were extracted from 65 Dutch pharmacy databases, representing 3% of the population (500,500 inhabitants). Questionnaires were sent to 5,002 patients, of which 2,312 were analyzed. The diagnosis of asthma and degree of asthma control were derived from questionnaires to identify patients with difficult-to-control asthma. Inhalation technique was assessed in a random sample of 60 adherent patients (prescription filling, ≥80%). Patients with difficult-to-control asthma, adherence to treatment, and a correct inhalation technique were qualified as having severe refractory asthma. Results were mirrored to the Dutch population.

Results

Of asthmatic adults, 3.6% (95% CI, 3.0% to 4.1%) qualified for a diagnosis of severe refractory asthma, representing 10.4 patients per 10,000 inhabitants.

Conclusion

The prevalence of severe refractory asthma might be lower than estimated by expert opinion. This implies that currently recognized severe asthma subphenotypes could meet the criteria of rare diseases.

Section snippets

Design

In this descriptive observational study we used a definition of severe refractory asthma based on recent international consensus criteria5 and estimated the prevalence of severe refractory asthma. In short, automated dispensing records from 65 community pharmacies in The Netherlands were used to identify all patients with at least 1 prescription for an inhaled corticosteroid (ICS) in 2011. In The Netherlands around 90% of the population obtains their medication from only 1 community pharmacy,

Results

Responders and nonresponders to the questionnaire did not differ with respect to OCS prescriptions (median of 0.99 mg [interquartile range, 0.57-2.3 mg] prednisone equivalent for nonresponders and 0.99 mg [interquartile range, 0.57-2.2 mg] for responders, P = .09). Adherence to ICSs was significantly lower in nonresponders (mean ± SD, 80% ± 56%) than in responders (mean ± SD, 84% ± 50%; P < .05).

Fig 2 shows that of 500,500 subjects included in the pharmacy database, 382,883 (76.5%) were adults.

Discussion

This study shows that 17.4% of the total asthmatic population had difficult-to-control asthma, which was defined as uncontrolled asthma despite the prescription of high-intensity asthma treatment. However, only 20.5% of these patients were adherent to their high-dose ICS prescription and had a correct inhalation technique, corresponding with only 3.6% of the total asthmatic population. This suggests that the prevalence of severe refractory asthma, as defined by international consensus, might be

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    Supported by Novartis Pharma B.V.

    Disclosure of potential conflict of interest: This study was funded by Novartis. M. L. Bouvy's institution has received funding from the SIR Institute for Pharmacy Practice and Policy. E. H. Bel has received compensation for board membership from Novartis, as well as consultancy fees from GlaxoSmithKline, Regeneron, and CIPLA and has received or has grants pending from Chiesi and GlaxoSmithKline, from which she has also received payment for delivering lectures. The rest of the authors declare that they have no relevant conflicts of interest.

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