Thus, drug interactions involving the inhibition of the S-enantiomer are considered more severe and may require pre-emptive dose adjustments or therapeutic interchange of alternative anticoagulants. Clinicians should reference a comprehensive drug interaction database when necessary. Patients receiving treatment with warfarin should have close monitoring to ensure the safety and efficacy of the medication. The PT is the number of seconds it takes the blood to clot, and the INR allows for the standardization of the PT measurement depending on the thromboplastin reagent used by a laboratory.
Routine assessment of INR is essential in the management of patients receiving warfarin therapy. The INR of a patient who is not on anticoagulation therapy is approximately 1. If a patient has an INR of 2. Most patients on warfarin have an INR goal of 2 to 3. However, specific indications, such as a mechanical mitral valve, require an INR goal of 2. The INR requires more frequent monitoring when starting warfarin. For hospitalized patients, INR monitoring commonly occurs daily.
Once a patient has reached the maintenance phase of therapy, the INR assessment is typically at least every four weeks but up to the provider's discretion. More frequent monitoring is necessary for patients with supratherapeutic or subtherapeutic INR to evaluate safety and efficacy.
Also, the INR requires assessment when initiating, discontinuing, or changing doses of medications known to interact with warfarin. Patients also require close monitoring for signs and symptoms of active bleeding throughout their treatment.
Close monitoring for signs and symptoms of bleeding, such as dark tarry stools, nosebleeds, and hematomas, is necessary. Monitoring liver function, renal function, and occult blood may be indicated in specific patient populations. Warfarin toxicity is assessable through signs and symptoms of bleeding, as well as the determination of a supratherapeutic INR level. The risk of bleeding is significantly greater with increased INR, especially above 5. When managing warfarin toxicity, the initial step would be to discontinue warfarin and then administer vitamin K phytonadione.
The vitamin K may administration can be either via the oral, intravenous, or subcutaneous route. However, the initial administration of oral vitamin K is often preferable in patients without major bleeding or extremely elevated INR.
A reduction in INR should occur within 24 hours of administration. After that, the recommendation is for intravenous vitamin K administration if necessary. Subcutaneous vitamin K is often not recommended for warfarin toxicity or reversal due to erratic and unpredictable absorption. All healthcare workers, including the primary care provider, nurse practitioner, and emergency department physician, need to know how to manage potential bleeding associated with warfarin.
After prescribing warfarin, patients require education regarding the importance of regular follow-up, foods that can interact with warfarin, and when to seek medical help. The prescriber should enlist the services of a pharmacist to help "dial in" the warfarin dose, and inpatients often have their INR and dose adjustment handled by a pharmacist. More importantly, healthcare workers need to be aware that today, there are other options instead of warfarin, including the novel oral anticoagulant drugs, which are deemed to be safer and require less intense monitoring.
Given the potential severity of warfarin toxicity, there needs to be an interprofessional team approach to prescribing and managing warfarin, including clinicians, specialists, pharmacists, and nursing staff, so positive therapeutic benefit has the greatest chance with minimal adverse effects.
This book is distributed under the terms of the Creative Commons Attribution 4. Turn recording back on. National Center for Biotechnology Information , U. StatPearls [Internet]. Search term. Affiliations 1 Massachusetts General Hospital. Continuing Education Activity Warfarin is a medication used in the prophylaxis and treatment of venous thrombosis and thromboembolic events. The most common anticoagulant used is Warfarin a.
Warfarin acts by blocking enzymes that facilitate the actions of blood clotting elements in the body. Hence, this avoids the blood from clotting. However, the action of the warfarin within the body may also vary, since it actively interacts with medications and certain food sources that we regularly take. This can lead to the blood thinning to an extent that it leads to profuse bleeding and eventual damage of various tissues.
Hence, when a patient is on warfarin, it is important to balance it with supplements that also maintain a certain level of clotting mechanism in the body. When a patient sends a blood test report, a commonly investigated test is prothrombin time.
Prothrombin is a key protein in the body which is produced in the liver and is responsible for the clotting of blood. A prothrombin time helps in knowing the time that the blood takes to develop into a clot. However, this factor can vary in patients who are on anticoagulant therapy. Hence, in order to standardize the results of prothrombin time, the INR was devised.
The INR is calculated by a formula that sees the prothrombin time of the patient be divided with normal prothrombin time. Indeed, this seems to be the case [ 8 ], but there are no good guidelines on how often patients should be monitored. Herein also lies a problem of resources: the more closely you monitor patients, the more expensive the direct costs to your service [ 9 ]. Of course, this does not take into account the savings that may be made through preventing hospital admissions from either under- or over-anticoagulation, but it nevertheless informs monitoring practice.
Consequently, the frequency of monitoring varies widely in different places [ 8 ]. The usual model of care of patients taking anticoagulants involves attendance at a physician-run hospital-based clinic. However, over the last decade there has been increasing interest in developing other models of care. These have included anticoagulation clinics based in primary care [ 10 ] and self-monitoring [ 11 ], both of which are as effective as hospital-based monitoring, or more so.
In this issue, Chan et al. This finding is consistent with US and UK comparisons of pharmacist- and physician-managed anticoagulant clinics [ 13 — 15 ]. Nurses are also safe and effective in managing anticoagulant clinics [ 16 ], which is reflected by the increased number of anticoagulant specialist nurses in the UK.
These findings do not indicate that physicians have inadequate knowledge or expertise in the trials many were experienced haematologists , but rather reflect the fact that there was often increased frequency of monitoring, contact time, and advice between clinic visits in clinics run by other health-care professionals, a luxury not afforded to physicians.
There can be no doubt that managing patients taking warfarin requires a multi-disciplinary and multi-functional approach. Patient education should be an important component, although surprisingly little attention has been paid to this [ 17 ].
Warfarin is associated with other adverse effects, including skin necrosis and hair loss. A population-based case-control study in suggested that warfarin treatment was associated with an increased risk of at-fault car crashes [ 18 ]. Since warfarin does not affect psychomotor performance, the finding was thought to be due to the diseases for which warfarin was being used, rather than a direct effect of warfarin itself.
However, the association between warfarin and road traffic accidents was not replicated in a recent study published in the Journal [ 19 ], and this is again emphasized in this issue [ 20 ]. Nevertheless, as Alvarez points out [ 21 ], assessment of whether drugs cause road traffic accidents is highly complex, and confounding by indication, concomitant medications, alcohol intake, and driving experience can all influence the findings.
It is therefore not surprising that replication of initial findings is often difficult. So where are we heading with warfarin prescribing? Warfarin will continue to be the oral anticoagulant of choice, possibly for the next decade, while we await an oral thrombin inhibitor that is both effective and safe.
In the meantime, there is increasing interest in improving warfarin dosage regimens by elucidating the environmental and genetic factors that determine dosage requirements. What to do when elective surgery is postponed. What happened to trusting medical experts?
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Heart Health DOACs now recommended over warfarin to prevent blood clots in people with atrial fibrillation. DOACs more effective, less finicky than warfarin Intensive efforts were underway for decades to develop alternatives to warfarin. DOACs less likely to cause life-threatening bleeding The major complication of taking any anticoagulation medication is bleeding.
Print This Page Click to Print. My cardiologist says I need to stay on Warfarin. You might also be interested in…. Harvard Heart Letter Be on your way to a healthy heart. Heart Health. Free Healthbeat Signup Get the latest in health news delivered to your inbox! Sign Up.
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