A Method to Calculate Adherence to Inhaled Therapy That Reflects the Changes in Clinical Features of Asthma.

Rationale Currently studies on adherence to inhaled medications report Average Adherence over time. This measure does not account for variations in the interval between doses nor for errors in inhaler use. Objectives We investigated whether adherence calculated as a single Area Under the concentration-time Curve (AUC) measure, incorporating the interval between doses and inhaler technique, was more reflective of patient outcomes than current methods of assessing adherence. Methods We attached a digital audio device (INCATM) to a dry powder inhaler. This recorded when the inhaler was used and analysis of the audio data indicated if the inhaler had been used correctly. These aspects of inhaler use were combined to calculate adherence over time, as an AUC measure. Over a 3 month period a cohort of asthma patients were studied. Adherence to a twice-daily inhaler preventer therapy using this device and clinical measures were assessed. Measurements and Results Recordings from 239 patients with severe asthma were analysed. Average Adherence, based on the dose counter was 84.4%, whereas the ratio of expected to observed accumulated AUC, Actual Adherence, was 61.8% (p