Warfarin is an anticoagulant medication commonly used to prevent blood clots and stroke in individuals with certain medical conditions such as atrial fibrillation, heart valve replacement, and deep vein thrombosis. It works by blocking the production of certain clotting factors in the blood. Warfarin is one of the most widely prescribed anticoagulants and has been in use for over 60 years.
This page looks at Warfarin side effects and litigation that has surrounded this medication.
History of Warfarin
Warfarin is a blood-thinning medication that was first introduced in the 1950s. It was initially developed as rat poison, incredibly enough. But was soon discovered to have anticoagulant properties and was later approved by the FDA for use as a medication to prevent blood clots.
The discovery of warfarin’s anticoagulant properties is credited to Karl Paul Link, a Wisconsin-based researcher who was looking for a way to prevent clots from forming in the blood of animals. In 1948, Link and his team identified a compound that was toxic to rats and called it warfarin. The name “warfarin” was derived from the words “WARF,” which were the initials of the Wisconsin Alumni Research Foundation, and “coumarin,” which was the name of the chemical class to which the compound belonged.
After warfarin was approved by the FDA, it quickly became one of the most widely used anticoagulants in the world. Today, it is used to treat and prevent a variety of conditions, including deep vein thrombosis, pulmonary embolism, and stroke. Warfarin is also commonly used in people who have a heart valve replacement or have been diagnosed with atrial fibrillation, a type of irregular heartbeat.
Despite its widespread use, warfarin has its challenges. One of the biggest challenges with warfarin is that it requires close monitoring and frequent blood tests to ensure the patient receives the right dose. This is because warfarin interacts with many other medications and foods, and even small changes in the dose can cause significant changes in the patient’s blood clotting time.
New anticoagulants have been developed in recent years that do not require frequent monitoring. But these newer drugs have weaknesses, too. One of the things we learned in the Pradaxa lawsuits is that some experts think well-managed warfarin (defined as TTR of 70-75% or more) is often a better course than drugs like Pradaxa. So Warfarin still has its place in a doctor’s arsenal to treat patients who need an anticoagulant.
How Warfarin Works
Warfarin interferes with the function of an enzyme (a protein) that is involved in the production of clotting factors using Vitamin K. This hinders the blood clotting process, causing it to take a longer time for the blood to form clots, reducing the risk of conditions such as stroke and deep vein thrombosis.
Vitamin K is essential for the normal functioning of the blood-clotting system, and warfarin interferes with its action, reducing the production of clotting factors and making the blood less likely to form clots. Warfarin is a slow-acting medication, and it may take several days for its full effects to be seen. This is why it is crucial for individuals taking warfarin to have regular blood tests to monitor their clotting ability.
Side Effects of Warfarin
While warfarin is a widely prescribed medication, it does have some side effects that individuals should be aware of. The following are some of the most common side effects of warfarin:
- Bleeding: One of the most significant side effects of warfarin is an increased risk of bleeding. This can occur anywhere in the body, including the skin, gums, nose, and intestines. In severe cases, warfarin can cause serious bleeding, such as a cerebral hemorrhage or a life-threatening bleed in the gut. Individuals taking warfarin should be careful when using sharp objects, such as razors and scissors, and should avoid contact sports.
- Skin reactions: Some individuals taking warfarin may develop skin reactions, such as rashes or itching. These reactions are usually mild and can be treated with over-the-counter creams or lotions. . Warfarin-caused skin death is a rare severe skin condition that affects around 1 out of 10,000 people who take warfarin. Within 5 days of taking the medication, patients may experience red and painful skin patches which can worsen into bleeding blisters, sores, and eventually lead to skin death. In severe cases like this, individuals may need to stop taking warfarin and switch to a different anticoagulant medication
- Altered taste: Some individuals taking warfarin may experience an altered taste, such as a metallic or bitter taste in their mouth. This rare side effect is usually mild and goes away on its own within a few days.
- Nausea and vomiting: Some individuals taking warfarin may experience nausea and vomiting, particularly when they first start taking the medication. These symptoms usually go away on their own within a few days.
- Joint pain: Some individuals taking warfarin may experience joint pain, particularly in the knees and hips. This side effect is usually mild and goes away on its own within a few days.
- Hair loss: Some individuals taking warfarin may experience hair loss, although this side effect is rare.
- Muscle weakness: Some individuals taking warfarin may experience muscle weakness, particularly in the legs. This side effect is usually mild and goes away on its own within a few days.
Drug Interactions with Warfarin
Warfarin can interact with other medications, and this can affect its effectiveness or increase the risk of bleeding. Because warfarin affects the body’s ability to clot blood, it can also increase the risk of bleeding. This risk of bleeding can be further increased by certain medications or supplements that interact with warfarin.
Here are some common drug interactions with warfarin:
- Anti-inflammatory drugs (NSAIDs): Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, can increase the risk of bleeding in people taking warfarin. They can also reduce the effectiveness of warfarin by inhibiting the production of prostaglandins, which are involved in blood clotting and create other complications.
- Antibiotics: Certain antibiotics, such as ciprofloxacin and metronidazole, can increase the risk of bleeding in people taking warfarin. They can also reduce the effectiveness of warfarin by altering the way the body metabolizes the drug.
- Antidepressants: Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine and sertraline, can increase the risk of bleeding in people taking warfarin. They can also reduce the effectiveness of warfarin by altering the way the body metabolizes the drug.
- Antifungal drugs: Antifungal drugs, such as fluconazole and itraconazole, can increase the risk of bleeding in people taking warfarin. They can also reduce the effectiveness of warfarin by altering the way the body metabolizes the drug.
- Vitamin K: Vitamin K is involved in blood clotting and can counteract the effects of warfarin. Therefore, people taking warfarin should avoid taking large amounts of vitamin K-rich foods, such as leafy green vegetables, or supplements containing vitamin K.
- Alcohol: Alcohol can increase the risk of bleeding in people taking warfarin. It can also reduce the effectiveness of warfarin by altering the way the body metabolizes the drug.
- Herbs and supplements: Some herbs and supplements, such as ginseng, ginkgo biloba, and St. John’s wort, can increase the risk of bleeding in people taking warfarin. They can also reduce the effectiveness of warfarin by altering the way the body metabolizes the drug.
It is important for people taking warfarin to inform their healthcare provider of all medications and supplements they are taking, including over-the-counter drugs and herbal products. This information can help healthcare providers make informed decisions about the safety and effectiveness of warfarin and avoid potential drug interactions.
Medical Malpractice Lawsuits Involving Warfarin
Because Warfarin can also cause serious side effects if not properly managed, Warfarin medical malpractice lawsuits are the result of failure to property use the medication. So patients who have suffered adverse effects from warfarin use have filed medical malpractice lawsuits against healthcare providers. Medical malpractice lawsuits involving warfarin can arise from several different issues, including:
- Overdosing: Warfarin is a medication that requires close monitoring and frequent blood tests to ensure the patient is receiving the correct dose. Overdosing can cause serious bleeding events and even death. If a healthcare provider fails to properly monitor a patient on warfarin and the patient suffers harm as a result, the provider may be liable for medical malpractice. Overdoses of warfarin can cause excessive bleeding, which can be life-threatening. Symptoms of a warfarin overdose can include prolonged bleeding from cuts or bruises, nosebleeds, heavy menstrual bleeding, blood in the urine or stool, and spontaneous bruising. Sometimes, the medical malpractice is not just the overdose but the failure to see the symptoms that would have allow the doctor to correct the problem before a more severe injury occurs. This often happens when the doctor fails to properly monitor a patient’s international normalized ratio (INR), which measures the level of clotting in the blood.
- Interactions with other medications: As we discuss above, Warfarin interacts with many other medications and can have dangerous consequences if taken together. If a healthcare provider fails to properly assess a patient’s medication regimen and prescribe a medication that interacts with warfarin, the provider may be liable for medical malpractice.
- Misdiagnosis: In some cases, a patient may be prescribed warfarin when they actually have a condition that makes the medication contraindicated. If a healthcare provider fails to properly diagnose a patient’s condition and prescribe warfarin, the provider may be liable for medical malpractice.
- Failure to warn: Warfarin can cause serious side effects, including bleeding, and it is important that patients are informed of these risks. If a healthcare provider fails to properly inform a patient of the risks associated with warfarin, the provider may be liable for medical malpractice.
Warfarin Settlements and Verdicts
Below are summaries of reported settlements and verdicts in cases involving injuries related to Warfarin caused by medical negligence by doctors or pharmacies.
$1,365,000 Verdict (Illinois 2022): 100-year-old female died of hypertensive cardiovascular disease which was allegedly caused by an acute Warfarin overdose. She died after ingesting 3 milligram Warfarin tablets instead of 1-milligram tablets over a 25-day period. Her family brought a wrongful death suit against the prescribing doctor for negligent medication management.
$250,000 Settlement (Pennsylvania 2020): 94-year-old female patient was diagnosed with Atrial fibrillation and was prescribed 1 mg Warfarin for treatment by the defendant doctor. When the defendant called in her prescription renewal, he accidentally renewed the Warfarin at 5 mg instead of 1. The incorrect dosage resulted in an overdose and the patient died.
$175,000 Settlement (Michigan 2017): 65-year-old male, died, reportedly of an acute subdural hemorrhage. Wrongful death lawsuit was brought against his doctors and health clinic, alleging that they negligently failed to recognize that he was taking Warfarin which put him at an increased risk of subdural hemorrhage.
$330,000 Verdict (Georgia 2013): reportedly suffered extensive bruising, extensive bleeding from his mouth and nose, severe anemia, shortness of breath, and a heart attack, and was admitted to the hospital on five separate occasions where he received multiple blood and plasma transfusions, after Walmart pharmacy incorrectly filled his prescription with Warfarin.
$110,000 Settlement (Pennsylvania 2012): 77-year-old woman died from a massive intra-cranial bleed from excessive Warfarin administration while under the care of nurses employed by the defendant. Lawsuit alleged that the nurses failed to follow protocol for monitoring Warfarin blood levels.
$206,000 Settlement (Michigan 2010): middle-aged female died from Warfarin toxicity allegedly caused by the negligent medical care provide by the defendants who prescribed excessive dosage.
Medical Literature of Warfarin Safety
Warfarin has been around forever but new studies keep coming out to fine tune when it should be used. Here are some of the recent Warfarin studies:
Lawal, O. D., et al (2023). Comparative Effectiveness and Safety of Direct Oral Anticoagulants and Warfarin in Patients With Atrial Fibrillation and Chronic Liver Disease: A Nationwide Cohort Study. Circulation, 147(10), 782-794.
According to a study published in the journal Circulation, direct oral anticoagulants (DOACs) were found to have a lower risk of hospitalization for ischemic stroke/systemic embolism and major bleeding compared to warfarin in patients with atrial fibrillation and chronic liver disease. The study was a new-user, retrospective cohort study that analyzed data from a large, US-based database between 2011 and 2017. The results showed that DOACs as a class were associated with lower risks compared to warfarin, but the incidence of clinical outcomes varied between individual DOACs and warfarin. The study concluded that more research is needed to determine the optimal anticoagulant treatment for patients with atrial fibrillation and chronic liver disease.
Ingason, A. B., et al (2023). Warfarin Is Associated With Higher Rates of Upper But Not Lower Gastrointestinal Bleeding Compared with Direct Oral Anticoagulants: A Population-Based Propensity-Weighted Cohort Study. Clinical Gastroenterology and Hepatology, 21(2), 347-357.
An Iceland population-based study compared the rates of upper and lower gastrointestinal bleeding between warfarin and direct oral anticoagulants (DOACs). The study found that warfarin was associated with higher rates of upper gastrointestinal bleeding compared to DOACs, but the rates of lower gastrointestinal bleeding were similar between the two types of drugs. The study also found that warfarin was associated with higher rates of major gastrointestinal bleeding compared to apixaban, but otherwise overall and major gastrointestinal bleeding rates were similar between warfarin and DOAC users. The study concluded that warfarin was associated with higher rates of upper but not overall or lower gastrointestinal bleeding compared with DOACs.
Wang, L., & Yao, W. (2022). A Cohort Study on the Safety and Efficacy of Warfarin and Rivaroxaban in Anticoagulant Therapy in Patients with Atrial Fibrillation Study. Biomed Research International, 2022, 4611383.
A study was conducted to compare the safety and effectiveness of warfarin and rivaroxaban as anticoagulant therapy in patients with atrial fibrillation. 96 patients were enrolled in the study and divided into two groups, the warfarin group and the rivaroxaban group. The warfarin group was given warfarin once a day and the dose was adjusted based on their international ratio (INR), while the rivaroxaban group received a fixed dose of rivaroxaban. The results showed that there was no significant difference in the number of embolism and bleeding between the two groups, but the total number of bleeding in the rivaroxaban group was lower than that in the warfarin group. The side effects were also similar in both groups. So the conclusion of the study is that rivaroxaban anticoagulant therapy has generally the same advantage in tolerance and prevention of thromboembolism as warfarin, but can effectively reduce the risk of bleeding in patients with atrial fibrillation.
Pokorney SD, et al. (2022). Apixaban for Patients With Atrial Fibrillation on Hemodialysis: A Multicenter Randomized Controlled Trial. Circulation 2022;146:1735-45.
This study, called the RENAL-AF trial, compared the safety and effectiveness of two blood thinners, apixaban and warfarin, in patients with end-stage renal disease who are on hemodialysis and have atrial fibrillation. The study found that taking apixaban 5 mg twice a day was just as safe as taking warfarin with the target international normalized ratio (INR) of 2-3. The rate of bleeding and strokes was similar between the two groups. The study was stopped early due to lack of funding – which happens a lot in the real world. The warfarin group had low INR levels, so it’s unclear if taking a lower dose of apixaban or not taking aspirin would have resulted in lower bleeding compared to warfarin.