Anti-coagulants Overview

Study Notes

Substances that prevent or delay blood coagulation
Types:
- In vivo: prevent blood coagulation inside the body
- In vitro: prevent blood coagulation outside the body

Methods to prevent blood coagulation outside the body:
- Cold: delays clotting
- Smooth lined vessels: prevent activation of Factor XII
- Decalcifying agents:
  - Potassium Oxalate: precipitates calcium oxalate
  - Sodium Citrate: combines with calcium to form unionized calcium compounds
  - EDTA (Ethylenediaminetetraacetic acid): chelates calcium ions
- Heparin

Heparin:
- Origin: animal
- Latent period: few minutes
- Duration of action: 4-6 hours
- Route of administration: intravenous or intramuscular injection
- Mechanism of action:
  - Inhibits prothrombin activator
  - Inhibits prothrombin
  - Inhibits thrombin (factors II, VII, IX and X)
- Site of action: in vivo and in vitro
- Anti-dote: protamine sulphate
Dicoumarol:
- Origin: plant
- Latent period: 2 days
- Duration of action: few days
- Route of administration: oral
- Mechanism of action: competitive inhibition of vitamin K
- Site of action: in vivo only
- Anti-dote: vitamin K

Bleeding disease characterized by spontaneous punctuate hemorrhages under the skin and mucous membranes (petechiae) - appearing as purplish spots
Types and causes:
- Thrombocytopenic purpura:
  - Due to decreased platelet count (below 50,000/mm³)
  - Causes:
    - Decreased platelet production (bone marrow damage)
    - Increased platelet destruction (hyperspleenism)
- Thromboesthenic purpura:
  - Due to abnormal platelets in circulation
  - Normal platelet count
- Idiopathic thrombocytopenic purpura:
  - Unknown cause
Characteristics:
- Prolonged bleeding time
- Normal coagulation time

Causes:
- Failure of absorption of vitamin K: e.g. intestinal diseases
- Failure of vitamin K synthesis in the intestine by intestinal bacteria:
  - Prolonged use of antibiotics
  - Newborn infants
- Dicoumarol toxicity:
  - Competitive inhibition of vitamin K by oral anticoagulants (dicoumarol)
- Severe lack of vitamin K in diet
Effects:
- Bleeding tendency due to inhibition of formation of factors II, VII, IX, X, protein C and S in the liver

Sex-linked, inherited bleeding disease
Characteristics:
- Transmitted by females to male infants
- Females do not suffer, making it sex-linked
- Severe and prolonged hemorrhage from injured vessels
- Prolonged coagulation time
- Normal bleeding time
Cause:
- Hereditary deficiency of coagulation factors - mainly VIII, IX, and XI, leading to bleeding tendencies
Types:
- Hemophilia A (Classic Hemophilia): deficiency of factor VIII - most common type
- Hemophilia B (Christmas disease): deficiency of factor IX
- Hemophilia C: deficiency of factor XI - rarest type

Feature	Hemophilia	Purpura
Heredity	Inherited	Not inherited
Affected sex	Male only	Both male and female
Cause	Lack of clotting factors VIII, IX or XI	Lack of platelet number or function
Types	Hemophilia A, B, C	Thrombocytopenic, Thromboasthenic, Idiopathic
Bleeding time	Normal	Prolonged
Coagulation time	Prolonged	Normal