How accurate are electronic monitors of metered-dose inhaler use?

Published Online: August 23, 2012

Electronic monitors of inhaled asthma therapy are suggested as the ‘gold standard’ for measuring patterns of medication use in clinical trials. These monitors can be capable of recording the number of times the inhaler is put into use, as well as the date and time of use to the nearest second. Several monitors of both metered-dose inhaler (MDI) and dry powder inhaler use have been developed and the first step in determining their internal validity is by undertaking ‘bench’ (laboratory) studies under standardized conditions. This not only provides data on their accuracy, but is also valuable in informing study protocols for their subsequent clinical trial use. Understanding the strengths and limitations of a monitor is therefore vital in determining its utility for future use by researchers.

In a Letter to the Editor in The Journal of Allergy & Clinical Immunology (JACI), Patel et al performed a detailed six-month validation of 22 Smartinhaler™ Trackers (Nexus6 Limited, Auckland, New Zealand), electronic monitors of MDI use. Monitors designed to measure both short-acting beta agonist (albuterol MDI) and combination inhaled corticosteroid/long-acting beta agonist (budesonide/formoterol MDI) use were tested. The researchers designed a testing protocol over eight-week windows that simulated various aspects of monitor use during a clinical trial. They initially screened monitors for malfunction, before then testing the monitors under both ‘low’ (simulated maintenance or low reliever use) and ‘high’ use conditions. Comprehensive checks of monitor accuracy in recording the number, date, and time of actuations were undertaken. Also, additional testing of data retention over an eight-week period, data download and battery charge were performed. The study was funded and performed independently of the monitor manufacturer and the pharmaceutical industry.

Two of the 22 monitors (9%) failed the initial screening process, as they recorded the date or time incorrectly, and were withdrawn from further testing. 2,170 of 2,176 actuations performed (99.7%) were correctly recorded, with 98.9% accuracy during low use and 100% accuracy during high use. Accuracy in recording date and time was similarly high (99.3%). 8 ‘extra’ actuations (of 2176 performed, 0.37%) were erroneously recorded by the monitors over 24 weeks. Data retention, data download and battery charge was 100% for the 20 monitors completing the full testing period.

Patel et al have demonstrated that this electronic monitor is highly accurate in recording MDI actuations in a strictly controlled laboratory setting, providing initial checks are performed to screen for faulty monitors. The strength of their validation process involves the testing of a variety of domains of monitor function over a prolonged period of time, and has allowed them to develop clinical trial protocols to safeguard data acquisition. This is of relevance to researchers using this, or similar MDI monitors, and to clinicians when interpreting information presented from trials using MDI monitors. This is the first step, information on monitor performance during ‘real-world’ use by patients is now required.


The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

AAAAI - American Academy of Allergy Asthma & Immunology