(From Pharm book and lecture, 31 Jan 2001, by Brian Buschman)
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Respiratory drugs are used primarily for asthma but also for acute bronchitis and COPD (other than asthma).
Drugs for the treatment of respiratory disorders include bronchiodilators to treat symptoms and others to treat the underlying condition.
Acute management include methylaxanthines like theophylline (low therapeutic index) and caffeine, sympathominetics (b-agonists like epi, ephedrine, albuterol, terbutaline and salmeterol) and antimuscarinics like ipratropium.
Underlying conditions are treated by respiratory stimulants like methylaxanthines (theophylline) and anti-inflammatories like cromolyn sodium, dexamethasone, triamcinolne, zileuton and zatirlukast.
Acute treatment of asthma always includes a b-agonist. Epi can be used but it has so many side effects that you should not use it. The same is true for isoproterenol and ephedrine.
b2- selectives are the best treatment. They include albuterol, terbutaline and salmeterol. The biggest problem with chronic asthma is that chronic use of b-agonists leads to tolerance when it comes to asthma.
It we used epi and isoproterenol they would be short acting. The ones we usually use are intermediate acting like albuterol and terbutaline. In cases of severe, frequent asthma during the night you can give the patient salmeterol to take before they go to bed. It has a long duration of action so it can help through the whole night but it’s not used for rescue because it has a very slow onset of action.
Other uses for b-agonists include COPD as needed and to delay premature labor.
Adverse effects of b-agonists include tremor, restlessness, tachy-arrhythmias. As the patient develops tolerance the asthma will appear to worsen.
Ipratropium is a quaternary ammonium anti-muscarinic. It is great with asthma because it does not really cross any cell membranes. This keeps it and it’s adverse effects local.
It’s bronchiodilation is less than that of b2 agonists for asthma but better for COPD making it the DOC. In addition to COPD it can also be used for rhinorhea.
It only has local effects such as cough.
Theophylline and caffeine (both from coffee) are the natural alkaloids of the methylaxanthine class. It acts by blocking adenosine receptors.
Theophylline is used with extreme caution in cases of severe asthma. It can also be used for Cheyne-Stoles respiration. The disorder involves a decreased sensitivity of the respiratory center to CO2 and this fits with that.
Effects of methylaxanthine include increased alertness, deferral of fatigue, decreased reaction time, increased capacity for learning. It also stimulates the heart and causes vasoconstriction. It makes you heart work harder and it makes you think more clearly.
At higher doses I stimulates insomnia, nervousness, positive ionotropic effects. The affects of methylaxanthine are those of coffee.
It also causes acid-stomach and bronchioconstriction.
In general the bad effects like acid-stomach, vasodilation and insomnia tend to undergo tolerance. Others like bronchiodilation of psyc stimulation do not experience tolerance.
With the small therapeutic range you need to watch out for drugs like cimetidine (OTC), erythromycin and zileuton (asthma) that decrease clearance. Be aware that oral contraceptives increase clearance.
Cromolyn sodium is has an uncertain mechanism of action but it prevents bronchospasm. It works by some form of blocking mast cells from degranulating and triggering the spasm.
It is used to prevent bronchospasm and can also be used in allergic rhinitis and conjunctivitis. With asthma it is used to prevent attack by administering cromolyn sodium before exercise.
It causes local irritation and dryness.
The main action of corticosteroids in asthma is to prevent inflammation.
Inhaled corticosteroids include triamcinolone, beclomothasone and flunisolide. These are not on the mini but you never know what might be on the shelf. Oral corticosteroids are also used for oral candidiasis but you can also treat that by frequent mouth rinsing.
Zileuton is the only lipoxygenase inhibitor on the market. IT is used for asthma and rheumatoid arthritis.
Zalfirlukast and montelukast compete for LtD4 and LtE4 receptors. They have anti-inflammatory effects. They are used for asthma, allergic rhinitis and aspirin hypersensitivity.
There are four levels of treatment for an acute asthma attack:
1) Use an inhaled b2-agonist.
2) If needed admit and use b2-agonist, O2, and IM corticosteroids.
3) Then add IV theophylline and inhaled ipratropium.
4) If still unresponsive use intermittent positive pressure ventilations until the body recovers on it’s own.
Mild asthma is defined as a FEV1 80-100% with intermittent symptoms of a persistent symptoms and an FEV1 of at least 70%. These patients experience symptoms less than 2/week and have nocturnal asthma less than 2/month. Treat mild asthmatics with a b2-agonist as needed or give them inhaled cromolyn to use before exercise. Consider zileuton (lipoxygenase inhibitor) as needed.
Moderate asthma has a FEV1 of 50-70% with symptoms more often than 2/week and nocturnal asthma worse than 2/month. They need the b2-agonist daily. Give them the b2-agonist, inhaled cromolyn or corticosteroids daily. Try cromolyn first because it has fewer nasty effects when compared to steroids.
Severe asthma has an FEV1 of less than 50% with lots of symptoms. Give it everything and refer them to a plumonologist. b2-agonist, corticosteroids, theophylline, ipratropium, salmeterol before bed and so forth.
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