Anticoagulants - Warfarin: Nursing pharmacology

Anticoagulants are medications that work by interfering with the function of clotting factors in the coagulation cascade, preventing the formation of thrombi, or blood clots.

These medications are used to prevent or treat thromboembolic events, such as deep vein thrombosis, pulmonary embolism, ischemic stroke, transient ischemic attack, coronary artery disease or myocardial infarction.

They're also used in clients with coagulation disorders, including antiphospholipid syndrome and disseminated intravascular coagulation; as well as in clients who underwent coronary angioplasty or cardiac valve replacement; and during surgical procedures like cardiopulmonary bypass, percutaneous coronary intervention, extracorporeal membrane oxygenation, and in clients undergoing dialysis.One of the most important anticoagulants is warfarin, which is given orally, and works as a vitamin K antagonist.

Normally, vitamin K is used by the liver as a cofactor for the synthesis and activation of the clotting factors II, VII, IX, and X, as well as the anticoagulant proteins C and S.

During this process, the active form of vitamin K, called vitamin K hydroquinone, is converted into vitamin K epoxide, which is then recycled back into vitamin K hydroquinone by another enzyme called epoxide reductase.

Warfarin antagonizes the function of vitamin K by inhibiting the epoxide reductase enzyme and preventing vitamin K hydroquinone from getting recycled.

As a result, there’s no synthesis and activation of the clotting factors II, VII, IX, and X, but also the anticoagulant proteins C and S.

Out of all the vitamin K-dependent proteins, protein C has the shortest half-life so it is the first to be depleted in clients taking warfarin.

This results in an initial period of hypercoagulation before the anticoagulant effect kicks in. To prevent this, bridging anticoagulation with LMWH is usually prescribed for a short period while starting warfarin therapy.Now, the main side effect of warfarin is undue bleeding, which can present as petechiae, ecchymosis, epistaxis, as well as bleeding gums, blood in stools, hematemesis, and uncontrollable internal bleeding from falls or even minor trauma.

Thankfully, antidotes are available to reverse the action of most anticoagulants if the bleeding gets severe. The antidote for warfarin is vitamin K1, also called phytonadione.

Other side effects of warfarin include hair loss, fever, bone marrow depression, and gastrointestinal effects like anorexia, abdominal cramps, vomiting, and diarrhea.

In addition, clients are at risk for thrombi and emboli in various parts of the body, since warfarin also inhibits protein C.

In particular, thrombosis of blood vessels in the skin leads to warfarin-induced skin necrosis, while microemboli in the feet can cut off blood supply causing purple toe syndrome.

Finally, warfarin is teratogenic, since it can cross the placenta and cause fetal hemorrhage, bone deformities, congenital heart defects, brain malformation in the fetus, or even spontaneous abortion.Now, due to the risk of bleeding, all anticoagulant medications are contraindicated in clients with active internal bleeding, recent trauma in the past three months, as well as those with a history of intracranial hemorrhage or ischemic stroke, gastrointestinal ulcers and coagulopathies or bleeding disorders.

In addition, anticoagulants should be used with caution in clients taking antiplatelet medications like aspirin and clopidogrel; or thrombolytic medications like alteplase, reteplase, and tenecteplase; which can increase the risk of bleeding.

Now, warfarin is broken down in the liver by a class of enzymes called CYP450, so it should not be combined with medications that interact with it.

On the one hand, any medications that inhibit this enzyme, such as cimetidine, omeprazole, metronidazole, trimethoprim/sulfamethoxazole, and amiodarone can cause the accumulation of warfarin in the body, leading to undue bleeding.

On the other hand, medications that enhance the activity of CYP450, such as griseofulvin, barbiturates, phenytoin, and carbamazepine, can speed up the metabolism of warfarin, decreasing its effects.

In addition, clients should limit their consumption of vitamin K-rich foods like green leafy vegetables, as they reduce warfarin's effects, as well as cranberry juice, as it increases warfarin's effects.

Warfarin is also contraindicated for use in clients undergoing surgery of the eye, brain, or spinal cord, as well as when undergoing spinal anesthesia or spinal puncture, as it can cause a spinal and epidural hematoma, which can lead to permanent paralysis.

Finally, warfarin is also contraindicated during pregnancy and breastfeeding due to its teratogenic effects.Alright, when caring for a client with a prosthetic heart valve who has been prescribed warfarin, first obtain a baseline assessment of your client, including vital signs, as well as any signs of bleeding, such as petechiae and ecchymosis.

Then, review your client’s recent laboratory test results, including CBC, PT, INR, as well as renal and hepatic function; and obtain a negative pregnancy test for female clients of childbearing age.Now, before your client begins warfarin therapy, remind them that prosthetic heart valves can increase the risk of clot formation, and explain how warfarin helps prevent clots from forming.

Be sure your client understands that they must take their medication exactly as directed to make sure their blood doesn’t clot too much or too little; if they miss a dose, advise them to contact their healthcare provider right away.

Also, let them know that they will need to follow up regularly to monitor their INR level.Next, discuss with your client that they may bleed or bruise more easily while taking warfarin, and review actions they can take to reduce the risk of bleeding, such as using a soft bristled toothbrush and flossing gently; using an electric razor for shaving; and being extra careful when handling sharp objects; as well as ensuring there are no tripping hazards around the home; avoiding hazardous activities like contact sports that could cause a physical injury; and always wearing a helmet during activities like bike riding.

For minor cuts, instruct your client to place a gauze or clean cloth over the affected area, and apply firm pressure for 15 minutes.

If they experience a nose bleed, they should tilt their head slightly forward, not backward, while applying pressure above their nostrils for 15 minutes.

Stress the importance of immediately notifying their healthcare provider if they are injured or if they hit their head; experience bleeding that is severe or lasts longer than 15 minutes; if they notice blood in their vomit, stool, or urine; as well as other warning symptoms like new onset of chest or back pain, shortness of breath, weakness, dizziness, or confusion.

Lastly, remind your client to inform all of their healthcare providers about their warfarin therapy, and to wear a medical alert identification at all times.

Then, explain to your client that some foods can alter the effectiveness of warfarin, and be sure to emphasize the importance of avoiding large day-to-day variations in the amount of vitamin K they include in their diet.

Instruct them to consume a consistent amount of foods high in vitamin K such as green leafy vegetables like spinach, kale, and broccoli, and provide them a list of foods with high, medium and low amounts of vitamin K to assist in meal planning.

Additionally, advise them to limit the amount of cranberry juice, grapefruit juice, and green tea they consume, and to avoid alcohol, cigarettes, and other nicotine products.

Lastly, advise your client to consult with their healthcare provider before taking any over the counter medications or supplements.Finally, during treatment with warfarin, be sure to monitor your client’s INR level, as well as for signs of bleeding, and evaluate for the therapeutic effect of an absence of thromboembolic events.Alright, as a quick recap...

Warfarin is an anticoagulant that is used to prevent or treat thromboembolic events. It does this by antagonizing the function of vitamin K, and as a result, there's no synthesis and activation of the clotting factors II, VII, IX, and X.

The main side effect of warfarin is undue bleeding, which can present as petechiae, ecchymosis, epistaxis, as well as bleeding gums, blood in stools, hematemesis, and uncontrollable internal bleeding from falls or even minor trauma.

When caring for a client taking warfarin, nursing considerations include performing a baseline assessment, monitoring for signs of bleeding, and evaluating for the therapeutic effect.

Client teaching is focused on safe administration, prevention and management of bleeding, and when to contact the healthcare provider.