Table 1 : Some of the main medicines, medicine classes and other agents that can interact with warfarin adapted from Juurlink, An erratic INR may reflect non-adherence to the medicine regimen, often due to misunderstandings of dosage requirements. A missed dose of warfarin is usually reflected in the INR result two to five days after the missed dose, 12 although a response may be seen within 16 hours.
In many cases, no explanation may be found for unstable INR values. It may be worthwhile discussing aspects of the dosing regimen.
Changes in the INR may also be the result of occult causes, such as undisclosed drug use, lifestyle and medical causes. Computerised decision support is a very useful tool for maintaining therapeutic INR levels in patients receiving anticoagulant treatment. There is evidence that computerised decision support can achieve improved therapeutic control in terms of INR, when compared with human performance.
A best practice Decision Support module has been developed for managing warfarin treatment, based on data from the Coventry system, 17 which has been widely accepted internationally. This module is available free to General Practices in New Zealand. It enables clinicians to more easily adjust oral anticoagulant doses and schedule follow-up consultations.
INR results can be tracked and monitored over time and a dose calendar can be printed for the patient. A meta-analysis of randomised controlled trials compared computerised decision support methods of determining warfarin dosage with traditional manual methods in patients. A randomised controlled trial compared the INR control by the percentage of time within-target of two groups of patients attending an anticoagulation clinic in Italy.
One of the advantages of computerised decision support tools is that information can be easily retrieved, providing many opportunities for clinical practice audit, including identifying patients who are on anticoagulant treatment but are not receiving INR monitoring. Transfer of the care of a patient on warfarin treatment from secondary to primary care is associated with a high risk for several reasons:.
Some New Zealand hospitals have developed protocols for the timely transfer of information about warfarin therapy to primary care on patient discharge. Essential details have been found to be:. New Zealand hospitals use a variety of warfarin initiation protocols and there is little evidence that one is any better than another.
It is recommended to follow on with the protocol initiated in secondary care for patients who start warfarin in this environment. It would be helpful for primary care clinicians to become familiar with local hospital protocols.
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Forgot your login? Login to my bpac. Remember me. Haematology Medicines management. Use of INR for monitoring warfarin treatment Regular measurement of INR levels is an essential component in the management of patients receiving warfarin treatment. In this article INR monitoring is essential for all patients treated with warfarin Managing warfarin treatment Computerised decision support Guide for over anti-coagulation 18 Transfer of care across the primary — secondary interface is associated with a high risk References In this article.
Key concepts: INR measurement is a key component in maintaining good control of warfarin treatment Practices should have clearly understood mechanisms in place to monitor patients treated with warfarin, to minimise the risks and maximise the benefits There is evidence that computerised decision support can achieve improved therapeutic control.
INR monitoring is essential for all patients treated with warfarin International Normalised Ratio INR testing is well established as an integral part of warfarin treatment. INR levels can be difficult to control Although regular testing of INR levels is essential for all people taking warfarin to maintain control of the INR, in practice, INR levels show considerable intra-patient variability. Maintaining good systems is important It is important that practices develop a standardised management protocol for all patients treated with warfarin, in order to optimise health outcomes, by achieving tighter control.
Managing alterations in the INR Some fluctuations in INR level can be expected, and for minor variations, changes in weekly doses are usually not required.
Changes in the INR level in a usually stable patient may be due to a number of reasons, including: 7,8 Major changes in diet or alcohol intake Drug interactions pharmaceutical or complementary Systemic or concurrent illness Non-adherence to dosage regimen Unknown causes.
Diet or alcohol Patients on warfarin are usually advised to consume a reasonably consistent proportion of vitamin K rich foods such as broccoli, spinach and cabbage. Drug interactions Many medicines and herbal products can interact with warfarin. Some, e. Increased bleeding risk without alteration of INR. There are many variables including genetic factors. This table does not include all possible interactions with warfarin.
Please check before prescribing or recommending any medicine, herbal product or food supplement. Systemic or concurrent disease Many systemic diseases can influence INR results: Congestive heart failure — may cause hepatic congestion of blood flow and inhibit warfarin metabolism, this may be particularly troublesome during exacerbations of heart failure.
Hypothyroidism — decreased catabolism of vitamin K clotting factors may decrease INR values. Hyperthyroidism — conversely, hyperthyroidism may increase catabolism of vitamin K clotting factors and increase INR values. Liver failure — may cause elevation of INR due to reduced production of clotting factors. Other illnesses — other intermittent conditions such as fever, vomiting and diarrhoea may affect the INR; ill patients may also reduce their usual dietary intake.
Please read on for more information. Warfarin also known by the brand names Coumadin and Jantoven is a blood thinner prescribed to prevent and treat blood clots.
Warfarin therapy may be prescribed for patients with certain types of irregular heartbeat, blood clots in the legs or lungs, and patients who have certain medical device implants such as artificial heart valves.
Warfarin must be monitored to ensure it is working effectively and being used safely. Achieving the correct warfarin dosage can be difficult but is extremely important. If the dose of warfarin is too low, the patient is at risk of developing harmful blood clots. If the dose of warfarin is too high, the patient may be at risk of serious bleeding. It can be monitored by drawing blood from a vein and sending the blood to an accredited laboratory to test, or it can be monitored by testing blood from a fingerstick with an INR test meter outside of a laboratory.
INR test meters may be prescribed to patients for use in the home, and they may also be used by health care providers at the point of care, such as a health care setting. Collins works in the anticoagulation clinic at BWH and helps patients on warfarin get set up with in-home INR testing. Collins also noted that this increase in time within therapeutic range may also be influenced by the types of patients who seek out in-home testing.
Whatever your reason for switching to home testing, the key is that you remain committed to testing your levels. There are several companies that provide the machines and patient training, including Acelis , Roche , and RCS. Patients who have diabetes will be familiar with this type of machine — it follows the same process as testing blood sugar. Most patients use an app or a website to send in their reports. The company will also manage billing and the insurance-related parts of the process.
When your provider receives your results, they can make dosage adjustments as needed.
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