Measurement properties of an asthma symptom and rescue medication use diary.

Introduction: Assessment of symptoms and rescue medication use are well-established endpoints for clinical trials evaluating asthma treatment.

Objective: To evaluate the measurement properties of an asthma symptom and rescue medication use (ASRMU) diary for clinical trials involving asthma patients aged ≥12 years.

Methods: Interviews with 35 patients were conducted to confirm the importance of key concepts in the ASRMU diary. Scores of symptom and rescue medication use were converted to symptom-free days (SFD) and rescue-free days (RFD). Test-retest reliability and equivalence (based on intra-class correlation coefficients [ICCs]) between paper-and-pencil and electronic (eDiary) versions were evaluated in a prospective study in 47 patients. Responsiveness of the ASRMU diary was evaluated through differences in percentage of SFD and of RFD by treatment group in eight asthma clinical trials that assessed inhaled corticosteroids (ICS) and long-acting β2-agonists (LABA), alone or in combination. A ninth placebo-controlled study calculated effect sizes. Minimal important differences (MID) were determined using anchor-based methods from two trials and by interviewing 11 patients.

Results: Patient interviews supported content validity for the ASRMU diary. Test-retest reliability was acceptable for SFD (ICC:0.70-0.75), but varied for RFD (ICC:0.58-0.78). Paper-and-pencil and eDiary modes of administration were equivalent (SFD, ICC=0.84; RFD, ICC=0.70). ICS/LABA had the largest percentage of SFD and RFD, followed by monotherapy and then placebo. MIDs were 7.7-14.7% for SFD and 8.4-15.6% for RFD.

Conclusions: The ASRMU diary captures the disease-specific concepts of greatest importance to asthma patients and provides important information for asthma diagnosis and treatment evaluation.