Adherence to asthma medications seen through a different lens: entropy

Adherence to the prescribed use of inhaled corticosteroids in difficult-to-treat asthma may need a rethink as it’s not as simple as doses taken versus doses prescribed.

According to an Australian study, new adherence metrics may help more fully describe patient behaviour regarding their inhalers and provide a stronger link between medication use and hard clinical outcomes.

The proof-of-concept study, published in Scientific Reports, involved electronic monitoring of inhaler use in 53 adults with difficult to treat asthma at The Alfred Hospital.

Entropy (H), a measure of disorder and previously used to describe day-to-day variability in breathing patterns and peak flow measurements, was calculated as a measure of irregular inhaler use. It was further broken down into increasing entropy Hinc or decreasing entropy Hdec.

The study found greater entropy, and particularly greater Hdec, was associated with more asthma attacks of all severities, whether requiring a visit to a general practitioner (Z=−2.43, p=0·015), oral corticosteroid treatment (Z=−2.508, p=0·012), and hospitalisation (Z=−2.07, p=0·038).

“That Hdec, rather than Hinc, has these relationships suggests that irregular drops in adherence may have more clinical impact than over-adherence,” the study said.

Other metrics such as average dosage or timing of gaps in medication were not associated with clinically important outcomes.

Lead author Dr Joy Lee, from The Alfred Hospital and Monash University, told the limbic the different way of looking at adherence would hopefully come into its own in the future, especially as electronic monitoring becomes integrated into inhaler devices.

As well, the data could be automatically synced with an online calculator for patients and clinicians to access in real time.

“I think some people see adherence as very black and white – patients are either taking their inhaler or they are not. The entropy data is more nuanced in terms of how the patient changes their use of the preventer inhaler on a day to day basis … and looking at the irregularity of inhaler use by measuring the entropy can be useful and associated with hard end points,” she said.

“If we can have a measure that can influence or help predict those patients who might be at risk, why wouldn’t we use it as a tool to help risk assess and manage our asthma patients?”

Dr Lee said ideally the study would be repeated in a bigger population, more centres and and maybe in other severities of asthma to make sure it is a repeatable signal.

“In the future if adherence monitoring does become more mainstream, that would give us more data as well.”

The study also re-introduced the concept of life-chaos to explain factors affecting medication adherence.

“While non-adherence can be intentional due to issues such as mistrust, lack of medication understanding, fixed beliefs and cost, unintentional disordered medication use may also indicate a corresponding degree of chaos in patients’ lives,” the study said.

“We speculate that the extent of entropy in controller use in difficult-to-treat asthma may also reflect overall life-chaos.”

Dr Lee said life-chaos has been studied as a barrier to care in other chronic health conditions including people with cardiovascular disease and HIV.

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