Researchers from Rice University and Baylor College of Medicine have identified patient errors that cause inhaler users to get about half as much medicine as they should from each dose.

The team said that clinicians have known for years that patients don’t use their inhalers as prescribed, but inhaler-dosing studies tend to focus on the rare cases when patients use the devices correctly.

“For years, we as clinicians have known that our patients do not use their inhalers as they should,” co-author Nick Hanania said in prepared remarks. “In the best case, a puff from an inhaler results in about 40% of the medicine reaching the lungs. In the worst case, if someone does everything wrong, that drops to 7%. We know the 2 extremes, but the vast majority of everyday use falls somewhere in the middle. In this study, we have been able to objectively measure the errors, and, using new technology, learn about their impact on drug delivery to the lungs.”

“Metered-dose inhalers are used every day by people with asthma, COPD and other chronic lung diseases, and the vast majority of the time – between 70% and 90% – patients make mistakes that keep some of the medicine from making it to their lungs,” co-author Ashutosh Sabharwal added. “While inhalers are the most efficient delivery mechanism for many patients, these devices require deft maneuvers on the part of patients. The common errors are well-known, but fixing them continues to be a challenge.”

The researchers suggested that errors are common among users because inhalers require precise and coordinated timing – a small deviation can have a significant impact on the amount of medicine that reaches the patient’s lungs.

Graduate student and co-author Rajoshi Biswas said patients often forget to shake the inhaler or don’t shake it long enough, particularly if they do multiple puffs. Other errors can include the timing, duration and force of their inhalation, as well as forgetting to hold their breath for 10 seconds to allow the medicine to reach their lungs.

The team modelled how much medicine reached the lungs of everyday patients by measuring the airflow characteristics from 8 patients as they drew breath. Using that data, Biswas programmed a machine to stimulate the flow, duration and force of a variety of breathing patterns.

The machine became a part of an experimental setup, which included a robotic finger to activate the inhaler and a metal tube to simulate an adult mouth and throat. The throat was designed to mimick the conditions that trap medicine in the mouth and throat of patients.

The team used the simulation to precisely measure how much medicine made it to the lungs in different scenarios where patients make common mistakes.

“The thing that matters the most is coordination,” Bismas said. “It’s vital to start breathing just before or at the exact same time the inhaler is activated. A delay of just a half second between pressing the inhaler and breathing in was enough to limit lung deposition to about 20% – about half of what a patient would get in the ideal case.”

When the machine started to inhale just before the inhaler was activated, Biswas noted that more than 35% of medication reached the lungs.

“In this situation, where timing is coordinated, the determining factor for lung deposition is the flow rate,” she explained. “Based on our findings, the ideal scenario is to inhale deeply at higher flow rates for about 3 seconds to fully inhale, and to activate the inhaler about a half second after starting to inhale. This helps ensure the medication clears the mouth-throat cavity and reaches the lungs.”