Patients who are new to anticoagulant therapy may be overwhelmed by the ongoing monitoring and lifestyle modifications which it entails. As such, it is important that sensible, comprehensible advice is given to the patient. Although warfarin therapy carries with it many benefits, there are also risks involved and the patient must be adequately equipped with knowledge to respond to any adverse or other incidents which may occur while they are taking warfarin. This article sets out the principal counselling points to give patients on warfarin therapy.

Compliance is key
"You cannot overemphasise the importance of compliance in warfarin patients," says Caitriona Gowing, who leads the hospital-based anticoagulation clinic at AMNCH Tallaght. As with all prescription medications, it should be emphasised that patients must follow precisely the instructions printed on the medicine label. Pharmacists should draw particular attention to the fact that warfarin should be taken at the same time each day. Gowing recommends that pharmacists advise patients to take warfarin in the evening as this facilitates the INR monitoring process.

While underlining the importance of compliance is imperative, it is important not to frighten the patient and reassurance should be given that a missed dose is not going to prove fatal! Specific advice should, however, be given on how the patient should respond in the event of a missed dose.
• Recommend that the patient takes the missed dose as soon as s/he remembers it. Obviously, this advice is dependent on when the patient remembers that s/he has missed a dose. If the time of the next dose is approaching when s/he remembers, it is important that the patient realises that it is not appropriate to 'double up' on the dose to compensate for the missed dose. Instead, s/he should skip the missed dose and continue with his/her dosing schedule as normal.
• The patient should remember to record the date of the missed dose and inform the doctor or pharmacist at his/her next visit to the anticoagulation clinic.
• If doses are missed for two or more days, the patient should contact the doctor immediately.

Side-effects
It is probably not a wise idea to document the side-effects - many of which are extremely rare - of warfarin to the patient. However, the pharmacist should note that haemorrhage, skin necrosis, purple toe syndrome, hypersensitivity, rash, alopecia, diarrhoea, jaundice, hepatic dysfunction, nausea, vomiting and pancreatitis are all potential side effects and should ensure that none of these present in a patient following commencement of warfarin therapy. The patient should be made aware, however, of the fact that - as warfarin prevents blood clotting - it may take longer to stop bleeding if s/he is cut or injured. Avoidance of activities which may cause injury is always prudent!

Keep INR in check
To optimise the safe usage of warfarin, regular monitoring of the patient's INR is essential. It is important that the patient understands this. When s/he begins anticoagulant therapy, it is likely that the INR will be monitored once or twice a week. With continued warfarin therapy, the INR will stabilise and, as such, INR monitoring will become less frequent. Caitriona Gowing gives eight weeks as the maximum interval between clinic appointments and emphasises that the patient understands the importance of keeping all appointments with the hospital or clinic.

Monitor other medicines
Warfarin's sensitivity to other drugs means that the introduction of a new medicine for a patient on warfarin should be kept in check by the anticoagulant clinic. For example, any broad-acting antibiotic has the potential to interact with warfarin. As such, the pharmacist should encourage the patient to attend the clinic within a week of starting the antibiotic. It is not a case of advising avoidance of antibiotics but rather emphasising the importance of keeping a close eye on the patient's INR while s/he is taking the antibiotic.

Likewise, OTC preparations should be used with caution. Patients on warfarin should ask the pharmacist's advice when seeking OTC medicines for the treatment of common ailments. Aspirin and NSAIDs such as Ibuprofen should not be taken unless prescribed for the patient. Miconazole oral gel (Daktarin™) should never be used in warfarin patients.

Vitamin supplements and herbal preparations can also affect the INR. Moderation of their usage should be encouraged and consultation with the health professional responsible for monitoring the patient's INR is essential. As far as multivitamins are concerned, it is worth noting that Vivioptal and Kiddie Pharmaton in liquid form do not contain vitamin K and are, thus, appropriate for use by warfarin patients.

In his article Warfarin - Some Practical Reminders published in the IPU Review of April 2003, Stephen Byrne gives the following advice regarding warfarin and other medicines: "A very simple rule of thumb is that any new medicine may either increase or decrease a patient's response to warfarin. Good practice when dispensing a new medicine for an orally anticoagulated patient is that they should contact the person who normally monitors their warfarin and arrange to have their blood monitored within 1-2 weeks of starting any new regular medicines."

Moderation in all things
Given the effects that foodstuffs, alcohol, OTC and herbal medications can have upon the INR, lifestyle advice is also critical for warfarin patients. Intake of dietary vitamin K should be kept in check. The normal Western diet contains 300 to 500 micrograms of vitamin K daily; only changes in the volume of consumption of vitamin K rich foods are relevant. Caitriona Gowing notes that the propensity to eat vast amounts of Brussels Sprouts at Christmas or spring cabbage can play havoc with a patient's INR. "As with most things with warfarin, it's all about consistent intake," she says. Patients should disregard claims that they "must never eat leafy green vegetables again!" They should, however, be aware that the any food with high levels of Vitamin K can alter their INR if eaten to excess. Consistent intake is always acceptable.

As an individual's liver status affects his/her ability to produce clotting factors, alcohol intake is a key concern for patients on warfarin. "Chronic alcohol consumption has been reported in literature as decreasing a patient's INR, whereas acute alcohol consumption increases it," writes Stephen Byrne in the cited IPU Review article. "Either chronic or acute alcohol consumption can result in errors when taking medication," he continues.

Caitriona Gowing says she gives the following advice to patients: "Regular alcohol consumption or not at all." She says that it is important to clarify what constitutes regular consumption, however, as patients may have their own interpretations! "Keep to two units a day," she says. This should be accompanied by two or three alcohol-free days every week.

Cranberry juice (not cranberries) can affect INR. Caitriona Gowing notes that "the constituents of different brands of cranberry juice may vary and as such may influence their likelihood of interacting with other medication." So, while consistent intake of one brand of cranberry juice may not affect the INR, switching between brands may have an effect.

In summary…
The patient on warfarin should:
• Carry the warfarin book with him/her at all times.
• Remind the doctor, dentist and pharmacist about his/her Warfarin at each treatment.
• Keep all hospital/clinic appointments.
• Take the warfarin dose at the same time each day, preferably in the evening.
• Keep a note of any missed doses.
• Not take an extra dose of warfarin to compensate for a missed dose.
• Avoid crash diets or binge drinking.
• Be consistent in intake of certain foods.
• Not take aspirin or other NSAIDs unless they have been prescribed for him/her.
• Never use Miconazole oral gel (Daktarin™).
• Look out for signs of bruising or bleeding.
• Ensure that s/he does not run out of his/her medicines.

Julie Cronin