In previous posts about the sympathetic nervous system (adrenergic effects) we mentioned the use of sympathomimetics as bronchodilators. Again, adrenergic bronchodilators are stimulating the Beta 2 receptors because that’s what causes bronchodilation. The side effect is that we also get the Beta 1 receptor stimulated so the patients are going to feel tachycardia, shakiness, etc. due to the beta 1 spill over. The best way to avoid beta 1 spill over and try to get primarily beta 2 out of it is to use it as an inhaler. If the person orally inhales the drug directly to the lungs, it goes directly to the site of action to the bronchioles and it doesn’t work systemically.
- Beta 2 property
- Beware of beta 1 spill over
Adrenergic Type Bronchodilators
- Epinephrine (Adrenalin) – inj, inhal
- Isoproterenol (Isuprel) – inj, inhal
- Albuterol (Ventolin, Proventil) – p.o., inhal
- Metaproterenol (Alupent) – p.o., inhal
- Terbutaline (Brethine, Bricanyl) – p.o., inhal., inj.
This list above is short-acting and rescue inhalers. By rescue inhalers this means the person is having difficulty breathing right now and needs immediate relief. Some long acting beta agonists work preventively. Most commonly the one we utilize is Albuterol. Albuterol will have the least beta 1 spill over. If you get beta 1 effects from just one puff, then you are very sensitive to it. Most people get that effect from overusing the drug.
Note: Almost all inhalers had to be reformulated because the FDA was concerned with the CFC’s in the inhaler affecting the ozone layer. They forced all the manufacturers to use a propellant that wouldn’t harm the ozone layer. The albuterols were all changed. They were changed to HFA’s, which is an alkene propellant as opposed to a fluorocarbon. First the manufacturers said we can’t meet the government deadline and meet it in the asthmatics at time. The govt said we’d give you a couple years to retool the drug. So a few years ago they were complete and most the asthmatics complained that they don’t feel the spray going in as powerfully and as deeply.