Heparin : things you should know

What is heparin?

Heparin is a naturally occurring anti-coagulant produced in human body by mast cells and basophils. This can also be manufactured for clinical use and this is the commonest anti coagulant in clinical practice.

History

Heparin was first isolated from dogs liver cell, thus the name hepar (liver) in. In 1916 Jay McLean discovered heparin. 

Types

Based on structure and difference in their pharmacological properties, heparin can be classified as:

  • Unfractionated (Avge size 15000 – 19000 Da) available since 1930
  • Low molecular weight (Avge size 3000 – 6500 Da) available since 1980
  • Ultra low molecular weight (Avge size <3000 Da) FDA approved in 2000

Mechanism of action

Unfractionated and fractionated / low molecular weight heparin both acts by potentiating the effect of the naturally occurring anti coagulant: anti thrombin III. 

Main clinical uses

  1. Acute coronary syndrome
  2. Venous thromboembolism (Pulmonary embolism & DVT)
  3. Acute cerebral infarction 

Dosing

LMWH:

Usual Therapeutic dose 1 mg/kg 12 hourly

Usual Prophylactic dose: Either 30 mg 12 hourly or 40 mg once daily

UFH can be given both in SC and IV route whereas LMWH is given in SC route 

Complications

  • Bleeding 
  • Osteoporosis
  • Thrombocytopenia
  • Allergic reaction
  • Elevated transaminases 

Monitoring

Usually heparin treatment doesnt require monitoring like VKA (warferin) but in situations where needed:

  • UFH is monitored via aPTT
  • LMWH is monitored via Anti Factor Xa antibody level

Remember both test can be done in both types of heparin but due to reason out of the scope of discussion here, one is preferred over the other.

Reversing

UFH can be reversed by protamine sulphate 

LMWH is partially reversed 

HIT

Heparin Induced thrombocytopenia is an emergency situation. By name, you may think it causes bleeding as heprin itself is an anti coagulant plus now it is causing low platelet but in reality it causes thombosis as well bleeding ( like in DIC or TTP). That is why some call this condition HITT – heparin induced thrombosis and thrombocytopenia. It can be 2 types:

  • Type 1 which happens within 2 days of administration of heparin and usually reverses.
  • Type 2 which takes place after 4-10 days of heparin use, immune mediated, Anti PF4 (platelet factor 4) antibody associated condition

This condition is diagnosed by 4TS screening 

  1. Thrombosis
  2. Thrombocytopenia 
  3. Timing
  4. Thrombocytopenia not explained by any other cause

HIT can be treated by:

  • Stopping the heparin
  • Switching to DTI (Direct thrombin inhibitor) like Argatroban
  • Bivalirudin can be used in PCI setting
  • IVIG can be be used as an adjunt in 1g/kg for 2 days dose

Do not give platelet as it may worsen the scenario unless advised by senior

Do not start warferin in low platelet situation

HIT incidence: 5%
Mortality: As high as 20%