Pharmacology, part 34: Endocrine Medications - Thyroid and Anti-Thyroid
by Cathy Parkes September 06, 2021 Updated: December 29, 2021 10 min read
In this article, we'll cover thyroid and antithyroid medications—drugs that either inhibit thyroid activity, or replace missing thyroid hormones. First, we'll give you a background on the thyroid and the related diseases of the thyroid, then we'll explain the medications, their modes of action, side effects, and nursing care.
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.
When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!
To understand thyroid and antithyroid medications, we'll give you a little bit of background on the thyroid, its hormones, the diseases that occur when its hormones are out of balance, and a related critical care intervention. This quick background will help you thoroughly understand the function of these medications. All of these topics are covered in our Medical-Surgical Nursing Flashcards.
What is the thyroid?
The thyroid gland is an endocrine gland located in the neck, and it releases three important hormones.
- Triiodothyronine (T3)
- Thyroxine (T4).
What do thyroid hormones do?
Triiodothyronine (T3) and thyroxine (T4) are thyroid hormones that control metabolism, growth and development, heart function, brain function, muscle function, digestion, and bone maintenance. T3 is the active form of T4. Check out our thyroid hormones full article.
Hypothyroidism is a disease marked by inadequate production of thyroid hormones T3 and T4 that causes the body to go into a hypometabolic state. Check out our hypothyroidism full article.
Hyperthyroidism is a disorder of the thyroid causing excess secretion of thyroid hormones T3 and T4 that causes the body to go into a hypermetabolic state. Check out our hyperthyroidism full article.
Grave’s disease is an autoimmune disorder that's the leading cause of primary hyperthyroidism. In Grave’s disease, your body creates antibodies that essentially trick your thyroid into growing and producing too much T3 and T4.
Thyrotoxicosis is an acute, life-threatening complication of hyperthyroidism known as a thyroid storm, with extremely high levels of thyroid hormones. This is usually brought on by infection, stress, diabetic ketoacidosis (DKA), or even after a thyroidectomy. Check out our thyrotoxicosis full article.
A thyroidectomy is a full or partial removal of the thyroid. This type of surgery is important to know about for your Med-Surg exams, because it can be the required intervention for several disorders, including hyperthyroidism, which can result from Graves’ disease. Check out our full article on nursing care following a thyroidectomy.
Thyroid medications - levothyroxine (Synthroid, T4), liothyronine (Cytomel)
Thyroid medications like levothyroxine and liothyronine are used to treat hypothyroidism. This class of drugs is named thyroid medications because they work to enhance the effects of what the thyroid would do, if it were functioning at optimal levels.
Levothyroxine will level up your thyroid levels.
Mode of action
Levothyroxine, and other thyroid medications in this class, act as a synthetic form of thyroid hormones to regain control over metabolism, growth and development, and other important functions like heart and brain health.
Usually, side effects with levothyroxine are minimal. But, if a dose of levothyroxine (or another thyroid medication) is too high, it could overcorrect and cause hyperthyroidism, the symptoms of which include anxiety, GI upset, sweating, unintentional weight loss, and heat intolerance.
Black box warning
It is important to note that although unintentional weight loss is a symptom of hyperthyroidism from a dose of thyroid medication being too high, these medications should not be used for the treatment of obesity or to help the patient lose weight. This class of drug carries a black box warning to warn against this off-label use.
If you have a patient taking thyroid hormones like levothyroxine, it is important to closely monitor their TSH and T4 levels. Periodically, their medication dose may need to be increased or decreased to help balance those hormone levels.
If you have a patient taking thyroid hormones like levothyroxine, they will need to be educated that lifelong treatment is required, so it is not a temporary prescription. Hypothyroidism is for life, and these medications replace the thyroid hormones that the body is not producing enough of.
Levothyroxine should be taken on an empty stomach with a full glass of water. Educate patients that they should take it before breakfast, with that full glass of water mentioned. If levothyroxine is administered to a patient in a hospital setting, it will likely be given around 6:00 am before breakfast is delivered.
Antithyroid medications are so named because they work to combat the effects of what the thyroid does, when it's too active. Here, we'll explain two important types of thyroid medications you'll need to know about for your pharmacology exams, NCLEX, and nursing practice: thioamides and iodine containing agent.
Thioamide - propylthiouracil (PTU)
Thioamide antithyroid drugs like propylthiouracil (PTU) are indicated for Graves' disease and can be prescribed for a patient in preparation for a thyroidectomy.
Propylthiouracil (PTU) - Prevents Thyroid from being Up too high.
Mode of action
PTU's mode of action is to block the enzyme thyroid peroxidase, which is an important ingredient in the process of the thyroid making T3 and T4. Blocking this enzyme prevents the synthesis of T3 and T4.
The side effects of thioamide antithyroid drugs like PTU include agranulocytosis (a decrease in white blood cell count which increases the risk of infection), GI upset, rash, and hepatotoxicity. If a dosage of PTU is too high for a patient, it can be too effective in lowering thyroid hormone levels and result in hypothyroidism.
The signs and symptoms of hypothyroidism are lethargy, weight gain, cold intolerance, bradycardia, and depression.
Black box warning
PTU carries a black box warning for its side effect of hepatotoxicity (toxic liver disease) and can be potentially fatal if untreated.
If you have a patient on a thioamide antithyroid like PTU, you will need to monitor their CBC levels because of the side effect of agranulocytosis.
CBC is complete blood count, and it's a combination of red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. If you are looking for fun ways to remember these, all of these expected ranges are covered in our Lab Values Flashcards.
If you have a patient on PTU it is also important to monitor their liver function. Keeping an eye on liver function can help avoid PTU's side effect of hepatotoxicity.
Iodine containing agent - strong iodine solution (Lugol’s solution)
Another antithyroid medication to be aware of is strong iodine solution, which is a combination of iodine and potassium iodiDe, also called Lugol's solution. Strong iodine solution is used to treat hyperthyroidism, thyrotoxicosis, and can be prescribed to a patient in preparation for a thyroidectomy as it also reduces vascularity of the thyroid and thus, potential blood loss during surgery.
It's called Lugol's solution because it was first made by a French doctor named Jean Guillaume August Lugol in 1829, initially as a cure for tuberculosis!
It is taken orally, and can be mixed with water or juice to mask the taste, which is not good.
Mode of action
The thyroid loves to absorb almost all of the iodine in the body. When strong iodine solution is administered, it is absorbed by the thyroid gland, and it then inhibits thyroid hormone production and release.
The exact mechanisms underlying this are uncertain, but the thyroid needs iodine as an ingredient for making thyroid hormones (a process called organification). However, there is a phenomenon in the body where when a huge amount of iodine is introduced, the thyroid stops organification (thus, more thyroid hormones are not made).
The side effects of the antithyroid strong iodine solution include GI upset, hypothyroidism (if it's too effective), hypersensitivity resulting in a rash or pruritus (itchy skin), or iodism.
You might be able to guess this, but iodism is the condition of having too much iodine, also known as iodine poisoning! Signs and symptoms of iodism include a metallic taste, stomatitis (inflamed/sore mouth), and severe GI upset.
If you have a patient using strong iodine solution, make sure you educate them to increase their fluid intake.
Iodine is also made into a radioactive solution called radioactive iodine, which is administered as a radiation treatment for patients with thyroid cancer. This may cause radiation sickness. Patients using radioactive iodine should limit contact with others so that they are not also exposed to the radiation.
Hi. I'm Cathy, with Level Up RN. In this video, I'm going to continue my coverage of endocrine system medications. Specifically, I'll be covering thyroid and anti-thyroid medications. If you have our Level Up RN Pharmacology Second Edition Flashcards, definitely pull those out and follow along with me. At the end of the video, I'm going to provide a quick quiz for you guys to test your understanding of some of the key facts and concepts that I'll be covering in this video. So definitely stay tuned for that.
So let's start by talking about our thyroid medications which include levothyroxine as well as liothyronine.
So these medications really act as a synthetic form of our naturally occurring thyroid hormones, and we would use them in the treatment of hypothyroidism.
So side effects are minimal unless the dose is too high. In that case, we may end up with signs and symptoms of hyperthyroidism.
So signs and symptoms can include anxiety, GI upset, sweating, weight loss, and heat intolerance if the patient has hyperthyroidism.
There's also a black box warning with this medication class to warn people that thyroid hormones are not to be used for the treatment of obesity or to help the patient lose weight.
In terms of the dosing, we're going to want to closely monitor the patient's TSH and T4 levels, and, periodically, we may need to increase or decrease their dose according to whatever those TSH and T4 levels are.
We also want to educate the patient that lifelong treatment is required with these thyroid medications, so it's not like they're going to take levothyroxine for a little while and suddenly their thyroid gland is going to produce sufficient T3 and T4. That's not going to be the case, so they're going to need to take this for the rest of their lives. The dose may need to be adjusted at times, but it will be lifelong treatment.
In terms of administration, we want to counsel the patient that they should take this medication on an empty stomach with a full glass of water before breakfast. So at our hospital, we wake our patients up at 6:00 AM and give them their thyroid medications with a full glass of water well before the breakfast trays are delivered to the floor.
So in terms of how I remember that these medications are used to boost up the thyroid hormone levels, if you look at the drug names levothyroxine or liothyronine, they both have that thyro, so T-H-Y-R-O. And that helps you to remember that these medications are used to treat thyroid disorders.
All right. Now, we're going to talk about anti-thyroid medications, and there are two different medications I'm going to talk about. The first is propylthiouracil or PTU.
So PTU is used in the treatment of Grave's Disease, which is a key cause of hyperthyroidism. It is also used in preparation for a thyroidectomy.
So PTU works by blocking the synthesis of thyroid hormones, so it helps to bring those levels down.
In terms of side effects, side effects include agranulocytosis, which is a decrease in granulocytes, which is a type of white blood cell.
So with this side effect, it does place the patient at increased risk for infection. Other side effects include GI upset, rash as well as hepatotoxicity, which is a black box warning for this medication class. Also, if the patient's dose of PTU is too high, it can cause signs and symptoms of hypothyroidism.
So this includes symptoms such as lethargy, weight gain, cold intolerance, bradycardia, and depression.
So as the nurse, when a patient is on PTU, you want to monitor their CBC levels because of that side effect of agranulocytosis. And we're also going to want to monitor their liver function because of that side effect of hepatotoxicity.
So the way I remember this medication and what it's for when I look at P-T-U, I think of prevents thyroid for being up too high, and that's exactly what it does. It prevents those thyroid levels from being up too high. It brings them down.
Another anti-thyroid medication to know is something called Lugol's solution, which is a strong iodine solution.
So this is a combination of iodine and potassium iodide, and it is used in the treatment of hyperthyroidism as well as thyrotoxicosis, which is a severe form of hyperthyroidism that's life-threatening. It could also be used in preparation for a thyroidectomy.
So Lugol's solution is absorbed by the thyroid gland, and there it inhibits the production and release of thyroid hormones.
Side effects can include GI upset, hypothyroidism and iodism.
So signs and symptoms of iodism include a metallic taste, stomatitis, which is inflammation of the mucosa in the mouth as well as severe gastrointestinal upset.
So this medication tastes really bad, apparently. I've never personally had it, but that's my understanding. So you can mix it with a lot of water or with juice to try to mask that taste.
Okay. Time for a quiz.
Question number 1. Levothyroxine should be given once a day with food. True or false?
The answer is... false. It should be given without food and a full glass of water before breakfast. So remember, we wake up our patients at my hospital at 6:00 AM to give them this medication with a full glass of water.
Question number 2. What anti-thyroid medication carries the risk for iodism?
The answer is... a strong iodine solution or Lugol's solution.
Question number 3. If a patient's dose of PTU - so that's propylthiouracil - is too high, what side effect would we expect?
The answer is...hypothyroidism. So remember, PTU prevents the thyroid from being up too high, so it reduces those thyroid levels. So if we do that too much, then the patient will end up with hypothyroidism.
Okay. I hope these quiz questions have been helpful. Hopefully, the video helped as well. If you got any of these questions wrong, just go back and review the flashcards or replay the video. I know you've got this, so take care and good luck studying. I invite you to subscribe to our channel and share a link with your classmates and friends in nursing school. If you found value in this video, be sure to hit the Like button and leave us a comment and let us know what you found particularly helpful.
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