Anticoagulants (Blood Thinners) : Types, Uses, Side Effects, & Contraindications

Anticoagulants (Blood Thinners) : Definition, Types, Classification, Example, List, Uses, Side Effects, Contraindications, & Interactions


  • Anticoagulants are drugs used to reduce the coagulability of blood.


Anticoagulants are used for prevention of thrombus extension and embolic complications by reducing the rate of fibrin formation.

  • They do not dissolve already formed clot, but prevent recurrences.
  • Heparin is utilized for rapid and short-lived action, while oral anticoagulants are suitable for maintenance therapy. Generally, the two are started together; heparin is discontinued after 4-7 days when warfarin has taken effect.



  • Apixaban
  • Argatroban
  • Bivalirudin
  • Dabigatran
  • Dalteparin
  • Enoxaparin
  • Fondaparinux
  • Tinzaparin
  • Rivaroxaban
  • Warfarin
Used in Vivo Used in Vitro

  • Heparin
  • LMW Heparin (Enoxaparin, Reviparin, Nadroparin, Dalteparin, Pamparin, Ardeparin, Fondaparinux)
  • Heparinoids (Heparan sulfate, Danaparoid, Lepirudin, Ancrod)
  • Heparin
  • Calcium complexing agents (Sodium citrate, Sodium oxalate)

Coumarin derivatives

  • Bishydroxycoumarin (Dicumarol)
  • Warfarin sodium
  • Acenocoumarol (Nicoumalone )
  • Ethylbiscoumacetate

Indandione derivatives

  • Phenindione


  • Deep vein thrombosis and pulmonary embolism
  • Myocardial infarction (MI)
  • Unstable angina
  • Rheumatic heart disease
  • Atrial fibrillation
  • Cerebrovascular disease
  • Vascular surgery, prosthetic heart valves, retinal vessel thrombosis, extracorporeal circulation, haemodialysis
  • Defibrination syndrome (Disseminated intravascular coagulation)


  • Bleeding disorders, heparin induced thrombocytopenia.
  • Severe hypertension, (risk of cerebral haemorrhage), threatened abortion, piles, g.i. ulcers (risk of aggravated bleeding).
  • Subacute bacterial endocarditis (risk of embolism), large malignancies (risk of bleeding in the central necrosed area of the tumour), tuberculosis (risk of hemoptysis).
  • Ocular and neurosurgery, lumbar puncture.
  • Chronic alcoholics, cirrhosis, renal failure.
  • Aspirin and other antiplatelet drugs should be used very cautiously during heparin therapy.
  • Oral anticoagulants should not be used during pregnancy.

Factors which enhance the effect of oral anticoagulants  should also be taken into consideration.

Drug interactions

Interactions are clinically important (may be fatal if bleeding occurs) and may involve more than one mechanism; the exact mechanism of an interaction is not always definable.

A. Enhanced anticoagulant action

  • Broad-spectrum antibiotics
  • Newer cephalosporins (cefamandole, moxalactam, cefoperazone)
  • Aspirin
  • Long acting sulfonamides, indomethacin, phenytoin and probenecid
  • Chloramphenicol, erythromycin, celecoxib, cimetidine, allopurinol, amiodarone and metronidazole
  • Tolbutamide and phenytoin
  • Liquid paraffin (habitual use)

B. Reduced anticoagulant action

  • Barbiturates (but not benzodiazepines), rifampin and griseofulvin
  • Oral contraceptives
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