The rescue inhaler for asthma is perhaps the most familiar form of aerosol therapy. When used properly, aerosol delivery of medication works more rapidly, produces fewer side effects, and is generally less expensive than systemic delivery by pills or injections. Respiratory therapists often get the job of training patients to use aerosol medications correctly.
The biggest challenge for the patient is to get the medication into the lungs without getting it stuck on the oral pharynx. The worst results have been observed in young children who cry when the medication is administered. Imaging studies show that most of the aerosol ends up in the mouth, esophagus, and stomach when the child is crying. When the same child is breathing quietly, the same aerosol can be deposited in the lungs with high efficiency.
The most effective technique for aerosol use is a deep, slow inhalation followed by a breath hold to allow the medication to settle into the airway. Check with your doctor if you're not sure you have the technique optimized.
Reference 1 reports a misconception that medication can be delivered by “blow by”, where the aerosol is delivered to a cloud in front of the patient's face. This is thought to be less disturbing for children, but experiments on mannequins show that when an aerosol mask is held just 2 cm from the open mouth, the efficiency of medication delivery falls by 85 percent.
Common types of aerosol therapy are small-volume jet nebulizer, pressurized metered-dose inhaler, and dry powder inhaler. For all types, the particle size should be between 0.5 and 5 micrometers. Smaller particles are likely to be exhaled, while larger ones are likely to stick to the upper airway and get swallowed. Dry powder inhalers are sensitive to humidity, which can cause the particles to aggregate.
Reference 1 reports that some patients check the amount of medication left in their pressurized metered-dose inhaler by shaking it or floating it in water. These methods are not reliable and may clog the valve with water. A dose counter is recommended as the most accurate way to know when the canister is empty.
Drugs already available in aerosol form include:
1. Anti-bacterial and anti-viral agents
2. Immunosuppressive agents
3. Surfactants
4. Prostaglandins
5. Mucolytics
6. Insulin
7. Vaccines
Drugs under development in aerosol form include:
1. Anti-fungal agents
2. Non-steroidal anti-inflammatory drugs
3. Anti-tussives (cough suppressants)
4. Heparin
5. Ergotamine
6. Calcitonin
7. Human growth hormone
8. Sildenafil
9. Antiproteases
10. Gene therapy vectors
11. Morphine
12. Fentanyl
Engineers are constantly striving to improve aerosol delivery devices to make them practical for more drug applications.
Reference:
Rubin BK, “Air and soul: The science and application of aerosol therapy”, Respir Care 2010; 55(7): 911-921.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.