Inaccurately determining when an inhaler is empty can reduce the effectiveness of aerosol therapy for patients with chronic obstructive pulmonary disease or asthma. A study found that more than one half of asthma patients did not know how many actuations their inhalers contained, and only 8 percent counted the number of actuations they had used. Only 15 percent of health care professionals and 17 percent of patients were able to describe an accurate method of estimating how much medicine remained. Rubin and Durotoye assessed how patients measured the amount of medicine remaining in their inhalers. They also measured the depletion of several inhaler canisters.

The first part of the study included new patients of a university hospital children’s asthma clinic. Patients were included if they used an inhaler regularly. The authors asked patients or their parents how they determined when to replace the inhaler. In the second part of the study, the authors evaluated four different inhaler canisters—fluticasone (Flovent), salmeterol (Serevent), albuterol (Ventolin), and beclomethasone (QVAR)—using the flotation method. The authors shook one half of the canisters before each actuation. All canisters were weighed at each stage (i.e., full, half empty as determined by number of actuations, empty as defined by the manufacturer, empty plus 20 percent as determined by actuation, and when no sound accompanied actuation). Each canister was immersed in water at each stage and the angle of flotation was measured. Water obstruction of the nozzle was determined using a dissecting microscope.

Fifty children and parents participated in the first portion of the study. Seventy-four percent did not know how many actuations their inhalers contained. All reported using the canister until they could no longer “hear” the medication. One half reported that they shook the canister before use. In the second part of the study, canisters that contained chlorof luorocarbon (i.e., albuterol, salmeterol, and fluticasone) had 86 percent more actuations than suggested by the manufacturers, whereas the canister with hydrof luoroalkane (i.e., beclomethasone) had 52 percent more actuations. Flotation was not accurate in determining when the canister was empty. Water obstruction of the nozzle was identified 27 percent of the time. Shaking the canister before actuation improved the number of actuations in chlorofluorocarbon canisters but had no impact in the hydrofluoroalkane canister.

The authors conclude that physicians are not teaching patients the importance of recognizing when the inhaler is empty and not informing them of the risks of using the inhaler more than suggested by the manufacturer. The authors suggest that the only accurate method is counting the number of actuations used and discarding the canister when the manufacturer’s recommendation is reached.