Pharmacology, part 10: Cardiovascular Medications - Anticoagulants Heparin & Warfarin
October 29, 2020 Updated: September 23, 2021 10 min read
In this article, we cover two important cardiovascular medications - heparin and warfarin, both of which are used to treat and prevent blood clots from forming in the body. 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.
IV/subcutaneous anticoagulants - heparin, enoxaparin
Heparin is an important anticoagulant medication used to treat and prevent blood clots from forming in people who have certain medical conditions or who are undergoing certain medical procedures. Anticoagulants make blood flow more freely.
Heparin can be used for things such as a stroke, a deep vein thrombosis (DVT), a pulmonary embolism (PE) or other thromboembolic disorders that require fast anticoagulation. It is also used to prevent blood clotting during open-heart surgery, bypass surgery, kidney dialysis and blood transfusions.
Heparin is a drug that can be administered through an IV or through a subcutaneous injection. A subcutaneous injection is a shot given directly into the fat layer between the skin and muscle and allows a drug to be absorbed slowly over a period of time.
Enoxaparin (Lovenox) is low molecular weight heparin used to treat and prevent the formation of blood clots but is only given subcutaneously and not through an IV.
Mode of action
Heparin works by activating antithrombin, which is a naturally occurring protein in the bloodstream that prevents us from clotting too much. It blocks our blood clotting mechanism by inactivating the major clotting protein thrombin. It prevents new clots from forming and existing clots from getting any bigger, but it will not break down clots.
If a patient is given too much heparin, or if it’s working too well, bleeding and bruising will occur. Immune hypersensitivity is also a possible side effect when using heparin.
Heparin-induced thrombocytopenia (HIT)
Heparin can also cause something called heparin-induced thrombocytopenia (HIT) which leads to decreased platelet counts. HIT is marked by a 50%+ reduction of platelets from the patient's baseline, so we need to monitor their thrombocyte count closely.
HIT is a very serious complication where a patient forms microclots. It can be confusing, because in this condition, heparin does the opposite of what it’s supposed to do—it’s supposed to decrease clotting, but in HIT it causes microclots. These microclots travel all over the body and cause ischemia to the appendages, turning toes and fingers black from lack of blood flow that can eventually cause them to fall off. Because the body is using all these clotting factors for microclots, the patient is at an increased risk for bleeding.
A patient who experiences HIT can never again have any form of heparin!
When administering heparin, it’s important to monitor a patient’s PTT levels. A partial thromboplastin time (PTT) test measures the time it takes for a blood clot to form in the body. When on an anticoagulant like heparin, PTT levels should be 1.5 to 2 times the normal baseline of 30 to 40 seconds. A PTT level above 80 seconds means there is too much anticoagulation and we should reduce the dosage.
To learn more about these lab values and many more, check out our lab values flashcards for nursing students!
The H in Heparin looks like two Ts put together, to remind you to monitor aPTT with Heparin
Antidote for heparin
Protamine sulfate is a medication used to reverse and counteract the effects of heparin. Protamine sulfate is a basic protein derived from fish sperm that binds to heparin to form a stable salt.
A patient receiving heparin therapy will need to be monitored for bleeding.
A real-world dosage calculation example for administering heparin can be found here.
Any patient who is on anticoagulants should also be placed on bleeding precautions and educated on what that means. Patients on bleeding precautions should use an electric razor and a soft-bristled toothbrush at home, and immediately report any signs of bleeding. These signs include oozing at the gumline, coffee-ground emesis (vomit), amber-colored urine, black/tarry stool, and large hematomas.
Patients should also be taught to seek emergency care for any head trauma, even if it is perceived to be small. In the hospital, nurses should minimize needle sticks, use small (22ga) needles, and assess the patient's output for signs of bleeding.
Oral anticoagulants (warfarin)
Warfarin (Coumadin, Jantoven) is an oral anticoagulant used to prevent heart attacks, strokes and blood clots. It can be used to treat a variety of thromboembolic disorders such as deep vein thrombosis (DVT), pulmonary embolism (PE) and atrial fibrillation (AFib). It can also be used following a myocardial infarction (heart attack), to help prevent complications.
Mode of action
Warfarin decreases the body’s ability to form blood clots by blocking the formation of vitamin K-dependent clotting factors. Vitamin K is needed for the body to make clotting factors and prevent bleeding. Therefore, by giving a medication that blocks the clotting factors, your body can stop harmful clots from forming and prevent clots from getting larger.
Warfarin is going to war on Vitamin K.
Like other anticoagulants, the main side effect to be aware of with warfarin is bleeding. Patients can also experience GI upset and hepatitis.
When a patient is on warfarin, their PT and INR levels should be monitored closely.
Prothrombin time (PT)
Prothrombin time (PT) measures how long it takes, in seconds, for blood to clot. More specifically, PT measures clotting time along extrinsic and common pathways in the “coagulation cascade.” The expected range of PT is usually between 11 and 13 seconds. When a patient is on warfarin, PT levels should be 1.5 to 2 times that amount or somewhere between 17 and 26 seconds.
International Normalized Ratio (INR) levels
The international normalized ratio (INR) is a ratio of a patient’s prothrombin time (PT) to the control PT. The expected range for INR a healthy patient is .8 to 1.1, meaning anywhere from 80-110% of the normal level.
When a patient is taking warfarin, their therapeutic INR should be somewhere between 2 and 3. It takes about 3 to 5 days on warfarin to get to that therapeutic level.
PT and INR levels are some of the many lab value ranges covered in our lab values flashcards. These cards were created so you can easily memorize the lab values you’ll need to know for Med-Surg, Pharm and more.
For the math nerds
If you are really good at algebra and following along, you might be a little confused...if warfarin PT levels are supposed to be 1.5-2 times the normal PT, and INR is a ratio of patient PT/normal PT, shouldn’t the warfarin INR ratio just be that same number, 1.5 to 2? It seems like this is simple algebra and we are moving the multiplier to the other side of the equation, however, that multiplier seems to become a different number.
- Normal PT levels x [1.5 to 2] = warfarin PT levels
- Warfarin PT levels / Normal PT levels = [2 to 3]?!
Congrats, you get a gold star! The reason the two multipliers are different is because of the N in INR. It’s the international normalized ratio. The ratio is normalized because it’s not just a simple ratio of one number divided by another number. The ratio is actually raised to the power of the ISI, or the international sensitivity index, which is different depending on what lab is measuring.
Heparin with warfarin
If a patient is in the hospital and they need anticoagulation to happen quickly, they can be given both heparin and warfarin concurrently. Heparin works right away while warfarin can take 3 to 5 days to get to a therapeutic level. Once at a therapeutic level, the patient can be discharged with a warfarin prescription.
This is sometimes referred to as "bridging" to warfarin, or "bridging therapies."
Antidote for warfarin
Warfarin works by decreasing the body’s ability to form blood clots by blocking the formation of vitamin K. Therefore the antidote to warfarin is to increase the body’s intake of vitamin K, effectively reducing the therapeutic level of warfarin.
To learn more about antidotes to medications, check out our pharmacology flashcards for nursing students.
Warfarin patient teaching
When a patient is on warfarin, it’s important to advise them to maintain a consistent intake of vitamin K. If their intake of vitamin K suddenly increases, then they may not have a therapeutic level of warfarin in their system. On the flip side, if they suddenly decrease their intake of vitamin K, they may be at higher risk for bleeding. During therapy it’s important the patient understands and is aware of their intake of vitamin K.
Foods that contain vitamin K are green leafy vegetables (K for Kale), vegetable oils, meat, cheese, fish and soybeans.
As with heparin, a patient will need to be monitored for any signs of bleeding such as tarry stools and coffee ground emesis.
In this video, we are going to continue on with cardiovascular medications, but we're going to turn our focus towards hematologic medications. So if you are following along with cards, I am on card number 28 in our Edition 2 Pharmacology flashcard deck.
Let's talk about anticoagulants that are given through the IV route or through the subcutaneous route.
So heparin is a very important medication that you really have to know inside and out. So heparin can be given through the IV route or the subcutaneous route. Then we also have enoxaparin, which is Lovenox, which is a low molecular weight heparin, and that is only given subcutaneously.
So we would use heparin for things such as a stroke, a DVT, a pulmonary embolism, or some other thromboembolic disorder that requires fast anticoagulation. So this heparin works very, very quickly.
It activates antithrombin, which inhibits thrombus formation. So it will prevent new clots from occurring, and it will prevent existing clots from getting any bigger, but it will not break down clots. And we will talk about a medication that will help break down clots. So heparin won't do that, but it will prevent new ones, and it will prevent existing ones from getting bigger.
Side effects. Anytime we have a medication, we can figure out what a key side effect is by thinking about what happens if that medication works too well. Right? So if we have too much heparin or it's working too well, we're going to have bleeding. So bleeding is a key side effect and a thing that we are going to be monitoring for.
In addition, heparin can cause something called heparin-induced thrombocytopenia or HIT. So this is a very serious complication where the patient forms all these little microclots, which travel all over the body and cause ischemia to the appendages, so their fingers and toes will turn black and eventually fall off. And then, because we're using up all these clotting factors with these microclots, the patient's at crazy risk for bleeding as well because we don't have any of these clotting factors. So HIT is a very, very serious complication of heparin.
In addition, hypersensitivity is a possible side effect with the use of heparin. So there are many key points to keep in mind with heparin. We're going to want to closely monitor the patient's APTT levels.
So my tip for remembering that you need to monitor PTT levels is that if you look at the letter H, it kind of looks like two Ts put together. And that can help you remember that with heparin, you monitor aPTT as opposed to PT/INR which we'll talk about here shortly.
So we're going to monitor the aPTT levels. Those PTT levels should be somewhere between 1.5 and 2 times the baseline.
So baseline aPTT is somewhere between 30 and 40 seconds. So if we take that and multiply it times 1.5 to 2, then we should see a PTT level between 45 and 80 seconds. If we get a PTT level that is above 80 seconds, like if it's over 100, that is a problem. That means we're doing too much anticoagulation with heparin, and we need to back off.
The antidote for heparin is protamine sulfate. You definitely have to know that.
And then of course, you're going to want to monitor your patient for bleeding during heparin therapy. So you're going to look for coffee-ground emesis which means there could be blood in their vomit, and you're going to look for tarry stools which is indicative that there may blood in the patient's stool.
Now, let's talk about oral anticoagulants. The medication to know here is warfarin, or Coumadin is the brand name for warfarin.
So warfarin can be used for a variety of thromboembolic disorders such as DVT, PE, AFib with a thrombus. It can also be used following a myocardial infarction to help prevent complications following an MI.
So it works by antagonizing vitamin K, which prevents the formation of several clotting factors.
So the way I remember warfarin as working on vitamin K is that warfarin is going to war on vitamin K, and vitamin K is like, "Why are you picking on me? I'm just a fat-soluble vitamin." And warfarin is like, "No, you're not. You may be a fat-soluble vitamin, but you are also an important component of the coagulation cascade." So that is why warfarin is going to war on vitamin K.
So a key side effect, I'm guessing that you can guess this, it's bleeding. Right? When we have an anticoagulant, if we have too much of it, we're going to end up with bleeding. So bleeding is a key side effect and what we're going to need to monitor for.
Other side effects include GI upset as well as hepatitis.
So when a patient is on warfarin, we're going to closely monitor their PT/INR levels. So we're not monitoring APTT levels we're monitoring PT/INR levels. And therapeutic INR should be somewhere between two and three. So it takes three to five days to get to that therapeutic level.
So when a patient's in a hospital and we need anticoagulation to happen fast, we start them on heparin right away, and then we also start them on warfarin concurrently. So the heparin works right away, and then we wait till they get to a therapeutic level with their warfarin, and then we can DC the patient home with a warfarin prescription because they're not going to be getting heparin at home. They're going to go home with warfarin.
So we're monitoring that PT/INR level. So PT is usually between 11 and 13 seconds. When a patient is on warfarin, we want to see that PT level at 1.5 to 2 times the baseline. So we would expect the PT level to be somewhere between 17 and 26 seconds. If it's over that, then we may have too much warfarin going on. We may need to decrease the patient's dose.
So the antidote for warfarin is vitamin K, right, the thing that it's going to war on, so definitely keep that in mind. With heparin, it was protamine sulfate. Here with warfarin, the antidote is vitamin K.
And then, we want to advise the patient to maintain a consistent intake of vitamin K. They're on warfarin, if they suddenly increase their intake of vitamin K, then we may not have a therapeutic level of warfarin. Right? We may not have enough of the anticoagulation that we need. If they suddenly decrease their level of vitamin K, then the patient may be at risk for bleeding. So during therapy, they should try to have a steady intake of vitamin K.
And, of course, we want to monitor for bleeding such as tarry stools or coffee ground emesis just like we did with heparin.
So I hope this video has been helpful to really help you very clearly understand the difference between these two anticoagulants. I can guarantee that you're going to need to know this for your nursing exams and as a registered nurse when you get done with school. Thanks for watching!
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