​Anticoagulants are medications prescribed for prevention or treatment of blood clots. They are sometimes referred as “blood thinners”, but they do not “thin” the blood. Instead, they delay the time for blood to clot, thereby slowing down the formation of blood clots. The most commonly prescribed oral anticoagulants are warfarin and nonvitamin K antagonist oral anticoagulants (NOACs) such as Rivaroxaban, Dabigatran and Apixaban. Anticoagulants also come in injectable forms such as heparin and low-molecular-weight heparin.

Anticoagulants stop certain clotting factors from forming or working. Different types of anticoagulants work in different ways. Warfarin block the formation of vitamin K-dependent clotting factors, while each NOAC blocks a different but specific blood clotting protein from functioning.

Anticoagulants are usually used in patients with:

  • Existing clots in the lungs, veins, arteries or heart
  • Irregular heart rhythm that may cause blood clots to form in the heart and increases the risk of stroke
  • Stroke
  • Recent surgery which limits the patient’s movement, such as a hip replacement or knee replacement, as the period of inactivity can increase risk of developing a blood clot
  • Heart valve replacement, as blood clots can form on the surface of the heart valve
  • Thrombophilia, a condition where there is increased tendency to form clots in the body, e.g. Factor V Leiden
  • Autoimmune diseases such as antiphospholipid syndrome where the immune system causes the blood to clot more easily
  • Other conditions that may increase blood clot risk such as Left Ventricular Assist Device implantation and Chronic Thromboembolic Pulmonary Hypertension

In particularly, NOACs have been approved for various indications:

  • Prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation and at least one additional risk factor for stroke
  • Treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE)
  • Prevention of recurrent DVT and PE
  • Postoperative venous thromboembolism prophylaxis (knee/ hip replacement surgery)

Dosing and Monitoring

Depending on the patient’s health condition and doctor’s assessment, anticoagulants may be prescribed for a duration of between three to six months, or even long-term. Patients should not stop their medication under any circumstances, unless otherwise advised by the doctors.

For patients who are on anticoagulants, it is crucial to check and monitor their International Normalised Ratio (INR), which is a test that measures the time it takes for blood to clot.

Dosage for the medications may be adjusted according to the desired INR that measures the effectiveness and impact of the medications. For instance, close monitoring may be required to determine the most appropriate dose of warfarin for each patient. The dosage may change after each visit, according to the INR results and patient’s conditions, such as onset of any illnesses, recent hospitalisation, changes in medication or lifestyle changes.

The dosage for NOACs is given according to patient’s kidney function; therefore frequent monitoring is required if the kidney function is weak.

Watching Out for Signs and Symptoms

The most common side effect of anticoagulants is the increased risk of bleeding. Patients should inform the doctor at the next visit appointment should they notice any signs of bleeding such as:
  • Bleeding from gums while brushing teeth (use a soft bristle toothbrush to minimise this)
  • Excessive menstrual bleeding in women (increased menstrual flow may be common but patients should check with their doctor if feeling unwell)
  • Nosebleed or prolonged bleeding from minor cuts despite applying pressure on the wound
They should contact their doctors immediately or admit themselves to the Emergency Department if they feel unwell, notice that the bleeding does not stop in 15 minutes, or experience any of the symptoms below:
  • Blood in urine or cloudy and dark urine
  • Black, sticky or tarry stools (not due to iron supplement)
  • Coughing up blood or coffee groundlike vomit
  • Unexplained large bruises or purplish area on skin
  • Sudden severe headache with nausea or loss of consciousness

NHCS Anticoagulation Clinic

NHCS Anticoagulation Clinic provides Patient Empowerment Programme (PEP) and POCT (Point-of-Care Testing) Programme for patients on warfarin therapy who require INR monitoring.

Suitable patients who have stable INR and do not require frequent testing, may be enrolled into the PEP to minimise their waiting time at the clinic. They may be scheduled for blood test only every two to three months and are empowered to monitor their INR. They do not need to attend the consultation clinic session if their INR is within desired range.

On the other hand, patients who have unstable INR and require frequent monitoring are enrolled under the POCT programme and required to own or loan a POCT device to perform INR selfmonitoring. This provide convenience for those who have difficulty in travelling to NHCS for frequent blood tests.

Patients are monitored and followed up through phone calls by specially trained pharmacists or nurse clinicians who will adjust the warfarin dose according to the home INR result.

Myths About Anticoagulants

❎ Patients on NOACs do not require regular laboratory monitoring.
✅ Fact: Although NOACs do not need monitoring to verify the efficacy of anticoagulation (unlike warfarin which requires INR monitoring), there is a need to do evaluations regularly to check on liver/renal functions, haemoglobin level, and medication compliance.

❎ Patient who takes warfarin should limit foods with high levels of vitamin K like dark, leafy greens.
✅ Fact: Patients are advised to maintain a consistent and balanced diet. There is no need to avoid foods with high levels of vitamin K totally.

❎ Self-testing does not provide results as precise as testing performed by a clinic.
✅ Fact: The accuracy of selfmonitoring with today’s Point-of-Care (POC) devices for anticoagulant therapy is comparable to laboratory measures, with favourable outcomes in anticoagulant control. The INR testing in NHCS uses POC devices that are recommended for INR range that is less than 3.5. A typical effective therapeutic range is between 2.0 to 3.0. When the INR range is higher than 3.5, patients will be required for blood test at the laboratory.

This article is from Murmurs Issue 35 (September – December 2019). Click here to read the full issue.