Pharmacology, part 4: Respiratory Medications - Expectorants, Mucolytics, Decongestants, Antihistamines
by Cathy Parkes April 28, 2020 Updated: December 07, 2022 4 min read
In this article, we cover some important respiratory medications including expectorants, mucolytics, decongestants and antihistamines. The Nursing Pharmacology video series follows along with our Pharmacology Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI and NCLEX.
Expectorants - guaifenesin
Guaifenesin is a medication used to treat a cough associated with respiratory infections. It’s available over-the-counter.
Mode of action
Expectorants like guaifenesin work by signaling the body to increase the hydration of, or pull water into, mucus secretions, which reduces their viscosity (makes them thinner) and easier to cough up. Thinner mucus flows more freely, so thinning out the secretions makes it easier to cough them out, making the cough more productive.
Check out Cathy’s easy way to remember guaifenesin.
The side effects with guaifenesin are usually minimal but can include GI upset and some dizziness.
When patients are taking guaifenesin, remember to instruct them to take it with a full glass of water. Remember that water is being pulled into the mucus secretions so hydration is another important part of the process!
Mucolytics - acetylcysteine (Mucomyst)
Acetylcysteine, or by the brand name Mucomyst, is a medication used for pulmonary disorders that have thick mucus secretions, for example, cystic fibrosis or bronchitis.
It can also be used as an antidote for acetaminophen overdose that results in hepatotoxicity.
Mode of action
Mucolytics like acetylcysteine work by breaking down the molecules in the mucus to help it become less viscous, which makes it thinner and easier to cough up. So both mucolytics and expectorants make mucus thinner and easier to cough up, but expectorants do it by hydrating the secretions, while mucolytics break down the molecules in the secretions.
An important side effect to know for acetylcysteine is that it can cause bronchospasm, which is a tightening of the airway smooth muscle marked by a wheezing cough. Use this medication cautiously in asthma patients, because they are already at risk for bronchospasm.
Acetylcysteine can also cause nausea, vomiting, and rash.
Some important patient teaching to know for acetylcysteine is to inform your patients that this medication smells like rotten eggs. Sorry! However, this doesn't mean that the medication has gone bad, it's a normal finding.
Decongestants - pseudoephedrine (Sudafed), phenylephrine
Decongestants are medications used to treat symptoms of rhinitis (nasal congestion). Pseudoephedrine, which you may recognize by its brand name Sudafed, and phenylephrine are two medications you should know for your Pharmacology exams, including the ATI, HESI, or NCLEX.
I am fed up with my congestion, so I'm going to take pseudoephedrine!
Mode of action
Congestion often occurs when the respiratory tract mucosa are swollen. Decongestants like phenylephrine and pseudoephedrine work by causing vasoconstriction of this respiratory tract mucosa. This vasoconstriction decreases blood flow and reduces the swelling.
Side effects of decongestants are very common and include like such as nervousness, palpitations, weakness, insomnia, and possible rebound congestion when you stop using pseudoephedrine or phenylephrine.
Pseudoephedrine and meth
If you have watched Breaking Bad, you know that pseudoephedrine is actually a key ingredient in methamphetamines (meth). Well, the feds know that too. In 2005, extra precautions were put in place around the purchase of pseudoephedrine in drugstores.
Pseudoephedrine is “over-the-counter” in that it IS available without a prescription, but it’s not usually stocked in the aisles of the pharmacy. You usually have to go to the pharmacy counter and ask the pharmacist for it. They’ll ask to see your drivers’ license, and your name will go in a database. If you are buying too much pseudoephedrine, they’ll think you might be making meth, and an alert will come up on your name and that will prevent them from selling you pseudoephedrine.
Due to the limits placed on pseudoephedrine, decongestants with phenylephrine have increased in popularity and so you will usually see a lot of those in the aisles.
You can remember the side effects of pseudoephedrine because they are like a minor version of what it would be like to use meth: nervousness, palpitations, and insomnia!
Antihistamines - 1st and 2nd generation
There are two generations of antihistamines that you need to know about and study for your Pharmacology exams. First-generation antihistamines include diphenhydramine (Benadryl). Second-generation antihistaminesinclude loratadine (Claritin), and cetirizine (Zyrtec).
Please note, because we are covering the respiratory system section of pharmacology, we are only covering H1-receptor agonist antihistamines. There are also H2-receptor agonists (like ranitidine, cimetidine, famotidine, etc.) but these antihistamines are used for GI issues, like heartburn.
Antihistamines are medications that are used to treat allergy symptoms such as rhinitis, itchy/watery eyes, or sneezing. Antihistamines can also be used for motion sickness as well as urticaria (hives).
Mode of action
Histamine is a part of your body’s immune response, normally released when your body detects something harmful, such as an infection. It causes blood vessels to expand and the skin to swell, which helps protect the body, but the result are all the symptoms from above: rhinitis, watery eyes, sneezing. Learn more: histamine and basophils.
H1-Receptor Antagonist Antihistamines work by competitively binding to H1 histamine receptors, preventing histamine from binding, and therefore blocking the histamine response in an allergic reaction.
When you are trying to remember the side effects for antihistamines, it's important to note that all antihistamines are three things: antihistamines, sedatives, and anticholinergic. But the intensity of these side effects vary from drug to drug.
With first-generation, you will get stronger instances of side effects like sedation, as well as those anticholinergic side effects which include dry mouth, constipation, urinary retention as well as photosensitivity.
With antihistamines, you should frequently assess their respiratory status, because if they're taking antihistamines for an allergy, you want to ensure the airway is remaining patent and not becoming worse due to anaphylaxis!
When you have a patient taking antihistamines that cause sedation, the nursing care precaution to take is to implement fall precautions.
The Pharmacology Video Series is intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI and NCLEX.
In this video, we are going to finish up with our key respiratory medications. I will be talking about expectorants, mucolytics, decongestants, as well as antihistamines.
So let's first talk about our expectorants. A key medication that falls within this class is Guaifenesin.
So guaif kind of sounds like cough, which is my way of remembering that Guaifenesin is used for a nonproductive cough associated with some kind of respiratory infection.
It works by reducing the viscosity of the secretions. So it helps to thin the secretions which makes your cough more productive.
Side effects are usually pretty minimal but can include GI upset as well as a little dizziness.
In terms of patient teaching, you want to teach your patient to take this medication with a full glass of water.
Now let's talk about mucolytics.
So the key medication in this class that I'd be familiar with is acetylcysteine, or Mucomyst is the brand name.
So this medication is used for pulmonary disorders that have thick mucus secretions, for example, cystic fibrosis.
It can also be used as an antidote for acetaminophen overdose. So acetylcysteine can be used for an acetaminophen overdose and acetaminophen is Tylenol.
The mode of action of acetylcysteine is to break down the molecules in the mucus to help it become less viscous.
Side effects can include bronchospasm, however, so you really want to use this medication cautiously in asthma patients. It can also cause nausea and vomiting as well as rash.
And you also want to give your patient a heads up that this medication kind of smells like rotten eggs. So one student gave me a little tip. Acetylcysteine starts with A, and this medication also smells like something that starts with A. So if that helps you to remember that, then that's great.
Now let's talk about decongestants.
The two decongestants that I would be familiar with include pseudoephedrine and phenylephrine.
So the way I remember pseudoephedrine is that I am fed up with my congestion, so I'm going to take pseudoephedrine. Pseudoephedrine is the generic name for Sudafed, which you may be more familiar with.
It is used for rhinitis or nasal congestion.
It works by causing vasoconstriction of the respiratory tract mucosa.
Side effects are very common and include things such as nervousness, palpitations, weakness, insomnia, and possible rebound congestion when you stop using pseudoephedrine.
Pseudoephedrine is actually one of the key ingredients in meth, so you can’t buy it just over the counter, like in the aisles of your drugstore. It's kept behind the pharmacy counter, so you need to go and ask for it. And they will ask to see your license and do some checking and make sure you're not buying too much of the stuff. So you can get it without a prescription, but it is behind the pharmacy counter because of all the meth issues in our country.
Also, over-the-counter cold products that you can find in the aisles usually contain phenylephrine instead these days because they're really trying to limit the use of pseudoephedrine.
To wrap things up, we are going to last talk about antihistamines.
So we have first-generation antihistamines, such as diphenhydramine, which is the generic name for Benadryl.
And then we have second-generation antihistamines such as loratadine, which is Claritin, and cetirizine, which is Zyrtec.
These medications can be used for allergy symptoms such as rhinitis, which is that runny nose, itchy, watery eyes, or sneezing. Antihistamines can also be used for motion sickness as well as urticaria which is a fancy name for hives.
Antihistamines work by competitively blocking H1 receptors which reduces the effect of histamine in the body.
Side effects are more common with first-generation antihistamines. There's not a lot of big side effects with second-generation antihistamines. With first-generation, you will get side effects such as sedation, as well as anticholinergic side effects which include dry mouth, constipation, urinary retention as well as photosensitivity.
So the way that I remember anticholinergic side effects is I remember the saying, "Can't pee. Can't see. Can't spit and can't poop." So these first-generation antihistamines definitely have those side effects.
If your patient is going to be taking diphenhydramine, or Benadryl, you're going to want to implement fall precautions because this medication causes sedation. So we need to keep our patients safe.
Okay. So that is it for our respiratory medications. I'd like to say that we will be able to get through our cardiovascular medications just as fast. But sadly, there's a big difference in the number of medications that are used for cardiovascular disorders versus respiratory. But we will get through it together, so hang in there with me. And I'll see you on my next video!
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