Asthma nebulizers don't deliver full dose

Nebulisers – devices that transform liquid asthma medications into an easy-to-inhale mist – aren't providing people with asthma a full dose of medication, according to a small new study.

Researchers found that less than 20% of the prescribed medication actually makes it into the lungs.

"Our study demonstrated that the prescribed dose bears little resemblance to the proportion of the drug children actually inhaled, and that [the amount they inhaled] was largely dependent on the formulation of the drug," said Dr Ahmad Kantar, head of the paediatric unit at the Institute Hospital Bergamo in Ponte San Pietro, Italy.

The study results were published online recently in the journal Respirology.

Different formulations

Although used less commonly than metered dose inhalers, nebulisers often are relied on in emergency situations and for younger children who may have a difficult time properly using a metered dose inhaler.

One potential problem with nebulisers, Kantar said, is that the machines and the medications are manufactured separately. With a metered dose inhaler, the delivery system is designed specifically for one medication. But a nebuliser has to be effective for different formulations of drugs, and that might lead to a difference in the amount of medication delivered, Kantar and his colleagues said.

The researchers enrolled 10 children to participate in a study to assess the amount of medication that's actually delivered. The children were an average of 9 years old, and all of them had well-controlled asthma.

The children inhaled each of three different corticosteroid medications. Corticosteroid medications are used to help prevent the inflammation that causes asthma flare-ups, but they are not used to control active asthma symptoms. Nebulisers can be used to deliver both types of medications.

Each drug was inhaled for a total of 10 minutes. The researchers used a filter to capture the amount of the drug that would be inhaled. Based on the particle size, they estimated how much of the medication might make it to the lungs. Filters were changed every five minutes.

Mouthpieces more effective

One-quarter or less of the medications were inhaled after 10 minutes, the researchers found. Even worse, only 16% of the drugs actually made it to the lungs.

Children inhaled 13% of the prescribed dose of fluticasone, 21% of beclomethasone and 25% of flunisolide, according to the study. When the researchers looked at how well the inhaled dose might make it to the lungs, they found that the amount of medication was as low as 5%, 8% and 16%, respectively.

Kantar said that many factors could affect how well a drug performs in a nebuliser. The water solubility and viscosity (how much it resists flowing) of a drug affect how it performs.

The way a child breathes also can affect medication delivery, as can the tool used to deliver the drug – a mouthpiece or a mask. Kantar said mouthpieces tend to be more effective.

"Medicinal products formulated for nebulisation should be characterized using a specified and standardized nebuliser system," Kantar said.

Calculating variables

One US expert said the bottom line is whether the child is responding to the medication.

"With any medication, what you take and what you end up with varies," said Dr. Jennifer Appleyard, chief of allergy and immunology at St. John Hospital in Detroit. "With inhaled medications for asthma or allergies, there's variation. Even in pills, there's variation in how much you absorb. But drug companies are calculating these variables and working with them."

"Our job isn't so much to analyse these details, but to see if the medication is working," she said. "What works for you or your child might not work for the next person, and we adjust accordingly."

Another expert pointed out how small the study was.

"There are so many confounding factors, it's impossible to say to use this drug over another because more was delivered to the lungs," said Dr. Len Horovitz, a pulmonary medicine specialist at Lenox Hill Hospital in New York City. That's especially true because this particular study included only 10 children, he said.

"I think this issue needs to be looked at a bit more, and the method of delivery and other factors need to be looked at in more detail," he said.

Informed interpretation

This study didn't compare metered dose inhalers to nebulisers, but both Appleyard and Horovitz said it's likely that the entire dose of medication from an inhaler doesn't make it to the lungs either. Both said, however, that drug companies have to take these factors into account before getting approval from the US Food and Drug Administration.

For his part, Kantar said, "Our study confirms the need for prescribers, researchers and regulators to have information on both the prescribed dose and the dose patients are likely to inhale from their nebuliser to allow informed interpretation of clinical effect and side effects."

More information

Learn more about asthma medications from the American Lung Association.

Picture: Asthma from Shutterstock

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