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Fondaparinux, Heparinoids and Direct Thrombin Inhibitors

Fondaparinux

Chemistry – synthetic pentasacchride

Mechanism of Action

Acts by inhibiting factor X.

Pharmacokinetics

Long half life of 17-21 hours.

Given parentally.

Uses

Used instead of heparin in cases where heparin induced thrombocytopenia occurs, as no HIT is seen with this.

Advantage – HIT

Disadvantage – antagonism

No antagonist acts, as protamine sulphate is ineffective.

Idraparinuxa sulfated derivative of Fondaparinux, having an even longer half life.

Heparinoids

These are related with heparin.

Heparan Sulfate

Natural –in mast cells

Commercially prepared as well.

The difference is that polymers of heparin sulphate are less modified than heparin.

Danaparoid is an example.

Advantage -HIT

Direct Thrombin Inhibitors

Mechanism of Action

Hirudin, Lepirudin and Bivalirudin are bivalent and bind to two sites on thrombin directly:

i. Active catalytic site

ii. Substrate recognition site

Argatroban and Melagatran are small molecules and bind only one site; the active catalytic site.

Source

Hirudin occurs naturally in leeches.

Rest are synthesized by recombinant DNA technology.

Monitoring & Pharmacokinetics

All are administered parentally. Therapeutic efficacy is measured by APTT.

Lepirudin

40% of the patients form antibody complex with lepirudin and these complexes are unable to be excreted through kidneys. They are given with caution in renally impaired patients.

Argatroban

It is metabolized by the liver, which is its main eliminating organ.

Thus patients with renal insufficiency are administered Argatroban, while those with hepatic insufficiency, Lepirudin.

Uses

  • In surgery for Reattachment of digits (even leeches were used)
  • HIT
  • Coronary angioplasty

Adverse effects

  • Renal
  • Anaphylactic reaction –with Lepirudin
Ximelagatran

It is given orally and is a prodrug. It is changed into Melagatran.

Advantage –HIT

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