An 8-year-old boy is brought to your office because of a chronic cough. His mother says that he coughs frequently throughout the day and will have symptoms 2 or 3 nights a month as well. This has been a problem on and off for approximately a year, but seems to be worse in the spring and fall. He also coughs more when he is riding his bike or playing soccer. He has been treated twice in the past year for “bronchitis” with antibiotics and cough suppressants but he never seems to clear up completely. His examination is normal except for his lungs, which reveal expiratory wheezing. You diagnose him with asthma and prescribe an albuterol inhaler.
- What is the mechanism of action of the albuterol?
- What are the most common side effects of the albuterol?
- What medications can be used to provide long-term control of the asthma symptoms?
Answers to case: agents used to treat asthma
Summary: An 8-year-old boy with asthma is prescribed an albuterol inhaler.
Mechanism of action of albuterol:
β2-Adrenoceptor agonist in bronchial smooth muscle causes smooth muscle relaxation, inhibits the release of mediators from mast cells, and stimulates mucociliary clearance.
Most common side effects of albuterol:
Skeletal muscle tremor, tachycardia, and cough.
Medications for the long-term control of asthma:
Inhaled corticosteroids, long-acting β2-adrenoceptor agonist, cromolyn or nedocromil; second-line agents include oral theophylline, leukotriene inhibitors, or systemic corticosteroids.
Asthma is a disease of chronic airway inflammation. This inflammation can cause episodes of wheezing, coughing, and breathlessness, which are reversible either spontaneously or with treatment. The inflammation can also increase bronchial reactivity to certain stimuli, such as allergens, infectious agents, or exercise, which may trigger bronchospasm and symptoms. Inhaled β2-adrenoceptor agonists (β-agonists) are widely used to treat the acute bron-chospastic episodes.
They work to relax bronchial smooth muscle via a cyclic adenosine monophosphate (cAMP)-mediated reduction in intracellular calcium concentrations, resulting in relaxation. The increase in cAMP also reduces the release of mediators from mast cells in the airways. Frequent use of these agents can result in a tachyphylaxis. Patients who require frequent dosing with inhaled β-agonists should also be treated with medications to reduce the frequency of bronchospastic events.
These include inhaled corticosteroids, long-acting β-agonists, cromolyn or nedocromil, and oral methylx-anthines, corticosteroids, or leukotriene modifiers. Inhaled β-agonists commonly cause tremor, tachycardia, and cough.
Approach to pharmacology of drugs used to treat asthma
1. Understand the medications used in the treatment of asthma, their mechanisms of action, and adverse effects.
2. Know the difference between short-acting symptomatic treatments and long-acting preventive therapies.
3. List the mediators of airway inflammation involved in asthma.
Constriction of the bronchial air passages, as a result of increased tone in airway smooth muscle cells.
Rapidly decreasing response to a drug following initial doses.