Coumadin

From Ask Dr Wiki

Contents 1 Mechanism of action 2 Therapeutic uses 3 Dose 4 Contraindications 5 Side effects 6 Drug interactions (not inclusive) 7 Comments 8 Pharmacokinetics

Mechanism of action

• Indirect-acting anticoagulants
• Anticoagulation by altering the synthesis of coagulation factors II, VII, IX, and X by interfering with vitamin K utilization

Therapeutic uses

• Treatment and prophylaxis
  • Deep vein thrombosis
  • Pulmonary embolism
  • Thromboembolic complications of Atrial fibrillation and cardiac valve replacement
  • Secondary prevention (death, recurrent Myocardial infarction, and thromboembolic events) in selected patients after Acute myocardial infarction

Dose

• Initial dose variable depending on
  • Patients age
  • Nutritional status
  • Dietary considerations
• Typical starting dose is 5 mg daily and adjusted based on international normalization ratio (INR)
• Maintenance dose
  • Based on patients response (INR)
  • Typically 2.5 – 7.5 mg daily

Contraindications

• Active bleeding
• Patients with lesions of the genitourinary or gastrointestinal tract, hepatic disease, Cerebrovascular accident, surgery, trauma, malignant hypertension, retinopathy
• Esophageal varices
• Threatened abortion, Eclampsia, Preeclampsia
• Recent surgical trauma to brain, eye or spinal cord
• Recent lumbar block anesthesia
• Arterial aneurysm
• Infective endocarditis
• Acute pericarditis
• Pericardial effusion
• Congenital or acquired coagulopathy
• Thrombocytopenia, blood dyscrasias
• Inadequate laboratory facilities
• Unsupervised senility, alcoholism, psychosis, or lack of patient cooperation

Side effects

• Bleeding
• Skin necrosis
• Purple toe syndrome
• Dermatitis
• Cholesterol microembolization
• Alopecia

Drug interactions (not inclusive)

• Antiplatelet medications
• IV anticoagulants
• Nonsteroidal anti-inflammatory drugs
• Amiodarone
• Quinidine
• Propafenone
• Metronidazole
• Rifampin
• Trimethoprim/Sulfamethoxazole
• Allopurinol
• Antifungals
• Erithromycin
• Quinolones
• SSRI
• Penicillin
• Quinidine
• Clofibrate

Comments

• Avoid large initial doses to reduce risk of skin necrosis secondary to the decreases in proteins C and S
• Maintain INR between 2 – 3 for most indications except for an indication such as anticoagulation for mechanical prosthetic heart valves, where the target range is 2.5 – 3.5
• Contraindications include
  • Pregnancy
  • Severe uncontrolled Hypertension
  • Unreliable patients
  • Bleeding diathesis
• Besides monitoring prothrombin time/INR values, monitor also for evidence of bleeding or bruising (e.g., hemoglobin, hematocrit)
• Avoid warfarin as initial treatment for Heparin induced thrombocytopenia (can cause thrombosis)

Pharmacokinetics

• Onset: 48 – 96 hours
• Half-life: 20 – 89 hours
• Elimination: hepatic