Dry powder inhalers are commonly misused.

CHICAGO -- Nearly one-third of patients with asthma or chronic obstructive pulmonary disease incorrectly used their dry powder inhalers in a study of 224 patients reported at the annual meeting of the American College of Chest Physicians.

The error rate increased with age, severity of airway obstruction, and lack of prior training, reported Dr. Siegfried Wieshammer, of the Ortenau Hospital Offenburg (Germany), and Jens Dreyhaupt, Ph.D., of the University of Heidelberg, Mannheim, Germany.

Dry powder inhalers, generally marketed as being easy to use, were developed in recent years to overcome the difficulties of using pressurized metered-dose inhalers, which require patients to coordinate actuation of the device with inspiration.

"We conclude that many health care professionals do know how to instruct their patients in inhaler use, but this is not done to the necessary extent," Dr. Wieshammer said. "The current proliferation of inhaler types may become detrimental to the quality of care, because busy doctors don't have sufficient time to become adequately familiar with the strengths, weaknesses, and pitfalls of all these new developments.

"Doctors should limit their selection to a small number of inhaler types [that have] operating principles they can study in detail, so they can teach their patients the optimal use," he added.

The investigators asked 224 newly referred outpatients reporting the use of four common dry powder inhalers (Aerolizer, Diskus, HandiHaler, and Turbuhaler) about the instruction they had received on using their inhaler and to demonstrate their technique. In all, 24 patients used more than one inhaler. The patients' mean age was 55 years (range 6-84 years).

At least one essential handling error that made a significant deposition of the medication to the lungs impossible was made in 32% of the 249 examinations. In some cases, patients exhaled into the devices rather than inhaled.

Aerolizer had the lowest error rate (9% of 22 visits), followed by Discus (27% of 86 visits), Turbuhaler (35% of 109 visits), and HandiHaler (53% of 32 visits), Dr. Wieshammer said.

The error rate increased significantly with age. Patients aged younger than 60 years had a 20% error rate, whereas those aged 60 years or older had an error rate of 42%. The error rate also increased with the severity of airway obstruction. Dr. Wieshammer speculated that cognitive deficits occurring with aging, as well as COPD-specific cognitive deterioration, make it difficult for older patients with advanced COPD to properly use their inhaler. The effect of age remained significant after adjustment for degree of airflow obstruction and type of training, he said.

Despite a number of high-quality training devices on the market, about one-third of the patients were referred only to the package insert, he said. Instruction by medical personnel on how to use the inhaler had a major effect on the error rate. Only 23% of trained patients made essential errors, compared with 52% of those who received no instruction, a statistically significant difference. This was somewhat surprising, as a lack of inhaler skills among health care professionals has been repeatedly described, Dr. Wieshammer said. There was no difference in error rates, whether the training was conducted by a chest physician or by other medical personnel.

With a risk-prediction model, the probability of inhaler misuse was only 9% in the favorable case of an 18-year-old patient with normal lung function and previous instruction who was being treated with Turbuhaler. At the other end of the scale, the probability of ineffective inhalation was 83% in an 80-year-old with moderate to severe obstruction and no prior instruction.

Dr. Wieshammer suggested that older patients with advanced COPD should be asked to demonstrate their inhalation technique at every health care encounter. If handling errors can't be eliminated by follow-up training, a metered-dose inhaler, in combination with a large-volume spacer, might be a valuable treatment alternative, he said.

Dr. Wieshammer disclosed that he has received funds from AstraZeneca Pharmaceuticals LP and GlaxoSmithKline Inc. for arranging educational courses and for speaking engagements in the last 12 months. Dr. Dreyhaupt reported that he has nothing to disclose.

BY PATRICE WENDLING

Chicago Bureau