Warfarin Therapy

Ampath National Laboratory Services
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💊 What is Warfarin?

Warfarin (also called Coumadin) is a blood-thinning medication used to prevent the formation of harmful blood clots.
It works by reducing the activity of vitamin K, which is needed to form clots.

Warfarin dosage must be carefully monitored because it is affected by:

• Your diet
• Other medications
• How your body processes the drug

🧪 The Role of the Lab

The lab monitors warfarin through a blood test called the INR (International Normalised Ratio).
This test measures how long your blood takes to clot.

• Your INR result determines your dose.
• The result is reviewed by a pathologist, who considers:
  • Your target INR range
  • Your previous INR history
  • Any new medications or conditions

🎯 What is the Target INR?

• Most people aim for an INR between 2.0 and 3.5, depending on their condition.
• Your doctor will specify your individual range.

🕒 How Often Should I Test?

• At the start of therapy: Every 2–3 days.
• Once stable: Weekly or monthly.
• After a new medication is added: Recheck within 3–4 days.

Let your clinic know if:

• You’re going away or travelling
• You’ve missed your test
• You’ve changed doctors

🩺 Why is Warfarin Prescribed?

Warfarin is used to prevent and treat blood clots, especially in the following situations:

• Heart conditions, such as:
  • Atrial fibrillation
  • Mechanical heart valves
• After surgery or trauma:
  • Hip or knee replacement
  • Fractures
• Clotting conditions:
  • Deep vein thrombosis (DVT)
  • Pulmonary embolism (PE)

📆 How Long Will I Need Warfarin?

The duration of therapy varies:

• It may be temporary (e.g. 3–6 months)
• Or lifelong, depending on your risk factors

📋 How to Take Warfarin

• Take your dose exactly as prescribed
• Take it at the same time each day (usually in the evening)
• Do not stop or skip doses without speaking to your doctor
• Avoid new medications, vitamins, or herbal remedies unless approved
• Store tablets in a cool, dry place, out of reach of children

❗ Missed or Extra Doses

If you forget to take your dose:

• Take it as soon as you remember on the same day
• If you remember the next day, skip it — do not double up
• Record the missed dose in your warfarin logbook
• Contact your clinic or doctor if you're unsure

If you took the wrong dose:

• Contact the INR Clinic or doctor immediately

📅 If You Miss Your Appointment

• Call your INR Clinic for a new test date
• If you're travelling, arrange monitoring before you leave
• If more than 3 months pass between tests, you’ll need a new referral

⚠️ Side Effects to Watch For

Warfarin’s main side effect is bleeding.
Call your doctor or seek emergency help if you notice:

• Blood in urine, stools, or from the nose
• Black stools
• Vomiting or coughing up blood
• Heavy menstrual bleeding
• Unusual bruising, rash, or red spots on skin
• Joint pain or swelling
• Severe headaches, dizziness, or confusion

Always wear a Medic Alert bracelet to notify emergency personnel that you’re on warfarin.

🚫 What Affects Warfarin?

Alcohol:

• Increases bleeding risk
• Do not binge drink
• Limit to:
  • 2 units/day for women
  • 3 units/day for men
• Avoid completely if you have liver disease

Food:

• Eat a consistent diet
• Limit or avoid:
  • Green leafy vegetables (spinach, kale)
  • Avocado, liver, broccoli, Brussels sprouts
  • Cranberry juice
• Do not suddenly increase or decrease your vitamin K intake

Other Medicines:

Warfarin interacts with many medications.
Tell your doctor or pharmacist before taking anything new.

Common medications that may:

• Increase INR:
  • Antibiotics, aspirin, antidepressants, anti-inflammatories
  • Antifungals, chemotherapy agents, thyroid meds
• Decrease INR:
  • Carbamazepine, rifampicin, St John’s Wort, oestrogens
• Have unpredictable effects:
  • Antivirals, corticosteroids, phenytoin

🤰 Pregnancy and Breastfeeding

• Warfarin is not safe during pregnancy
  • Contact your doctor immediately if you become pregnant
• Warfarin is generally safe while breastfeeding

📞 Getting Your Dosage

After your blood test:

• You will be contacted with your new dose
• If your blood was drawn after 3pm, your result may be available the next morning
• If you don’t hear from the lab by the evening, call them

Update your contact information every time you visit the clinic.

✅ Final Reminders

• Stick to your dosing and testing schedule
• Be aware of foods, medications, and activities that may affect your INR
• Seek help immediately if you notice bleeding or feel unwell
• Always consult your doctor if you’re unsure