What are the indications, dosage and precautions of warfarin?💊💊💊

More and more new oral anticoagulants are being developed. As an older oral anticoagulant, warfarin has disadvantages such as large individual dose variability, narrow therapeutic window, interactions with many drugs and foods, and the need for drug monitoring in patients when used. Warfarin has so many disadvantages. Should it be eliminated from anticoagulation? Although there are many new anticoagulant drugs, it does not mean that warfarin can be completely replaced. Warfarin still plays an important role in anticoagulation therapy. 

What kind of medicine is warfarin?

Warfarin is an anticoagulant drug derived from dicoumarin. Vitamin K epoxide reductase is inhibited by warfarin. This will limit the synthesis of coagulation factors II, VII, IX, and X to produce anticoagulant effects. In addition, some anticoagulant proteins are also inhibited by warfarin. Therefore, patients may experience transient procoagulant effects during the initial period of treatment with warfarin. Its clinical manifestations are gangrene of the limbs and skin necrosis. They generally appear on the third to eighth day after dosing.

What are the indications for warfarin?

It can be used to prevent and treat pulmonary embolism and deep vein thrombosis. It also prevents thromboembolic complications following myocardial infarction, atrial fibrillation, heart valve disease, or prosthetic valve replacement. For patients with mechanical valve replacement, moderate to severe mitral stenosis, or bioprosthetic valve replacement in the first 3 months, warfarin is an irreplaceable alternative to other novel oral anticoagulants.

Dosage of warfarin.

The starting dose of warfarin is generally recommended to be 1 to 3 mg once daily. Certain patients with congestive heart failure, high risk of bleeding, impaired hepatic function, or the elderly require individual dose adjustment. Their starting dose can be reduced as appropriate. Rapid anticoagulation is required for diseases such as venous thromboembolism. Patients need to use unfractionated heparin or low molecular weight heparin overlapping with warfarin for 5 to 7 days. Patients were given warfarin immediately on day 1 or day 2 of heparin. Adjust the drug dose until the INR reaches the target value for more than 2 days before discontinuing parenteral anticoagulants. 

Indications	INR target range	Course of treatment
Venous embolism	2.5 (Range 2 to 3)	Patients secondary to transient risk factors require 3 months of use. Patients with unprovoked venous embolism need to use it for at least 3 months. After 3 months, the risk-benefit ratio of the patient's treatment was evaluated before deciding whether to extend the course of treatment. Long-term treatment is required for patients with two unprovoked venous embolisms, and the risk-benefit ratio of treatment is regularly assessed.
Myocardial infarction prognosis	2 to 3	For patients at high risk of myocardial infarction, combined use of low-dose aspirin is recommended for at least 3 months. (Daily take ≤100mg aspirin)
Atrial fibrillation (non-valvular and valvular)	2 to 3	It recommends long-term anticoagulation in patients at intermediate and high risk of stroke. Nonvalvular atrial fibrillation: Warfarin is not the drug of choice for these patients. The treatment plan needs to be determined based on the evaluation. Valvular atrial fibrillation: Warfarin is the drug of choice for these patients. Most new oral anticoagulants are contraindicated in patients with atrial fibrillation complicated by moderate-to-severe mitral stenosis, mechanical valve replacement, or bioprosthetic replacement (the first 3 months).
Mechanical valve replacement	The INR range needs to be adjusted appropriately according to the valve type and location, and it is generally 2 to 3.	Lifelong treatment.
Bioprosthetic replacement	2 to 3	It is generally 3 to 6 months. After 3 months of treatment, patients can be switched to new oral anticoagulant drugs or discontinued according to the situation.

Pharmaceutical monitoring of warfarin.

Efficacy monitoring:

INR (International Normalized Ratio) and PT (Prothrombin Time) are its main monitoring items. INR can evaluate its anticoagulation strength, and the general target range of INR is 2 to 3. 

Adverse reaction monitoring:

The main adverse reaction of warfarin is bleeding. Although a patient's risk of embolism increases with increased bleeding risk, the benefit of anticoagulation is generally greater. Therefore, bleeding should not be considered a contraindication to anticoagulation. Reversible factors that increase their bleeding risk should be screened for and corrected for in patients who require anticoagulation but are at greater risk of bleeding. They should also strengthen their monitoring and conduct regular evaluations. 

Compliance Monitoring:

Compliance monitoring is mainly to monitor whether the patient takes the medicine on time and according to the dose, and whether there is any self-adjustment of the dose.

Instructions for dosing warfarin.

Dosing time: Warfarin is recommended to be taken at a fixed time in the evening. It is mainly due to the fact that pharmaceutical monitoring is generally performed during the day. When patients take warfarin at night, the dose can be adjusted immediately based on monitoring results.

Dosage: After the patient's INR reaches the target and is stable, frequent dose adjustments are not required. However, the patient should record each dose adjustment and the next monitoring time.

Precautions while taking the medicine:

1. Missed dose: The patient should make up the dose immediately unless it is close to the next dose. A single dose should not be doubled in the event of a missed dose.
2. Diet: In the past, patients were told to avoid foods containing vitamin K as much as possible. However, more and more studies have pointed out that as long as the daily diet structure is relatively stable and do not suddenly consume large amounts of foods containing vitamin K, the efficacy of warfarin will not cause much impact.
3. Self-monitoring: Patients should monitor themselves for signs of bleeding or embolism.
4. Pregnancy and lactation: Warin is generally not recommended for patients during pregnancy. Low molecular weight heparin is preferred for pregnant patients. Patients can continue to use warfarin while breastfeeding because it does not pass into breast milk.