So, let's talk about bronchodilators. Now bronchodilator
action is limited to taking that constricted inflammed airway
and opening it up. The drug binds to the beta 2 receptor in
the lung and it stimulates cyclic AMP in smooth muscle cells.
Those smooth muscles relax in the bronchial muscle
and you get dilatation.
Now, obviously you're not fully treated because
those airways are still kind of thick, aren't they?
Short acting beta agonists generally
last less than 6 hours such as albuterol.
Long acting beta agonists or LABAs act over 24 to 48 hours
sometimes 12 hours. These are salmeterol, formoterol and so on.
Those drugs are used once or twice a day. Now, there is a drug
specifically indicated for COPD that is also in the beta agonist list
but we are going to leave that alone for now.
Toxicity of bronchodilators is pretty rare.
You can sometimes get tachycardia or tremor
and sometimes you can get hyperexcitibility, but as I said,
because these are inflammed agents,
you're not really going to have a lot of symptoms.
Methylxanthines are purine derivatives.
Now caffeine is a methylxanthine.
So, when you think about effects and side effects,
think about caffeine on your own body.
Theophylline is the prototypical respiratory methylxanthine.
These drugs act by inhibiting phosphodiesterase.
And PDE3 activates bronchodilation. When you have these drugs
on board, you may also increase diaphragmatic strength.
Two cups of coffee can actually cause bronchodilation
so you can understand that these drugs may be quite potent.
The side effects are the same as drinking too much coffee.
Gastrointestinal distress usually manisfested by cramping.
Tremor and insomnia. A toxicity of these agents can be arrhythmia
and low blood pressure. And vomiting is also a potential side effect.
The antidote for these medications is beta blockers because
you want to block the effects of hyperadrenergic states.
The next class of drugs are the muscarinic agents. The prototypical
drug is ipatropium which is sold commonly as Atrovent.
When you look at the colour of puffer,
its universal colour is going to be green or a green cap.
This agent will block muscarinic receptors in the airways.
This prevent bronchoconstriction caused by vagal discharge.
So they may not be particularly effective
if they have already constricted.
They may be used both in children and in adults.
And these agents have no anti-inflammatory action.
The toxicity is minor atropine like effects
so the toxicities are almost non existence.
They do not cause tremor and they do not cause arrhythmia
which distinguishes these drugs from the beta agonists.