Flashcards in Katzung 12th ed - Chapter 20 - Respiratory, Asthma (1.5) Deck (16):
There are three broad categories of drugs that directly trigger bronchodilation. Name these three categories, with one example each.
- Sympathomimetics (beta-agonists)
- Methylxanthines (e.g. theophylline)
- Anti-muscarinics (e.g. ipratropium, atropine)
List three beta-agonists used (rarely) in asthma that are NOT beta-2 selective.
Adrenaline, Isoprenaline, Ephedrine.
List two beta-2-selective agents that are used in asthma.
How do beta-agonists cause bronchodilation?
Binding to beta-adrenoceptors activates adenylyl cyclase to produce cAMP, which relaxes smooth muscle.
How do methylxanthines cause bronchodilation? (and is there a second way?)
Methylxanthines (such as theophylline) inhibit the breakdown of cAMP by inhibiting phosphodiesterase (PDE). The increased levels of cAMP cause bronchodilation. (Another way they contribute to bronchodilation is by competitive inhibition of adenosine, which would otherwise cause bronchoconstriction.)
How do anti-muscarinic agents cause bronchodilation?
Anti-muscarinics such as ipratropium antagonise the effects of acetylcholine. Without ipratropium, vagal stimulation would result in acetylcholine release, which causes bronchoconstriction and mucus secretion.
Apart from theophylline, what is another methylxanthine that is worth knowing about?
Name some of the minor and major toxicities of theophylline. Which electrolytes can it affect?
Minor: headache, nausea, vomiting, insomnia
Major: seizures, arrhythmia, death
Electrolytes: hypoMg, hypoPO4, hypokalaemia
How can theophylline be administered?
Oral or IV.
What is the Vd for theophylline?
0.3 - 0.7 L/kg
What is another name for isoprenaline?
What are the effects of methylxanthines on:
- skeletal muscle
- Positive inotrope
- Positive chronotrope
- Weak diuretic
- Causes increased strength of skeletal muscle contraction
How can salbutamol initially cause transiently decreased PaO2?
Because it has vasodilator activity, and it thereby increases perfusion to poorly ventilated lung units.
What does ketamine do to the airways?
It is a bronchodilator.
Explain how corticosteroids are useful in preventing asthma exacerbations.
Corticosteroids are NOT bronchodilators. They reduce bronchial reactivity, by reducing the infiltration with lymphocytes, eosinophils and mast cells.