Pharmacology for Dentistry

Coagulants and Anticoagulants 245

heparin like effect by degrading fibrinogen
into an unstable form of fibrin.

Danaparoid containing mainly heparan
sulfate isolated from porcine intestinal
mucosa and is used in heparin induced
thrombocytopenia and deep venous
thrombosis.

Lepirudin is a recombinant derivative
of hirudin (direct thrombin inhibitor
secreted by salivary glands of leech). It
inhibits thrombin directly and is mainly
used in heparin induced thrombocytopenia.

HEPARIN ANTAGONISTS

The agents like protamine sulfate react
with the strongly acidic groups of heparin
and can abolish its anticoagulant activity.
Approximately 1 mg of protamine sulfate
neutralizes 80 to 100 units of heparin. It is
used only in severe bleeding or when
heparin action needs to be terminated
rapidly e.g. after cardiac or vascular
surgery.

ORAL ANTICOAGULANTS

They act by interfering with synthesis of
vitamin K dependent clotting factors in liver.
They act as competitive antagonists of vitamin
K and reduce plasma levels of clotting factors
in a dose dependent manner. They act by
interfering with regeneration of active form
of vitamin K. Factor VII levels are reduced first
followed by factor IX, X and II.

ACENOCOUMAROL

It takes at least 48 to 72 hours for the
anticoagulant effect to develop fully.

Acenocoumarol is absorbed nearly
completely after oral administration. It is

highly bound to plasma proteins and it

crosses the placental barrier.

Adverse effects include haemorrhage,

rash, alopecia, diarrhoea, hepatic dysfunction,

nausea, vomiting and pancreatitis.

It is used in venous thromboembolism,

pulmonary embolism, atrial fibrillation and

for prophylaxis after insertion of prosthetic

heart valves.

WARFARIN

It is most commonly used oral anticoagulants

employed for long term anticoagulant therapy

and having less toxic effects including alopecia

and dermatitis. It is rapidly and completely

absorbed from intestines and is 99% plasma

protein bound. It crosses the placental barrier and

is secreted in milk. The other properties are same

as acenocoumarol.

PHENINDIONE

The mechanism of action and adverse

effects are same as acenocoumarol. It

produces more serious nonhaemorrhagic

toxic effects, their use is now very limited.

FIBRINOLYTICS

These are agents used to lyse clot to

recanalise occluded blood vessels, mainly

used in coronary arteries.

STREPTOKINASE

It is a purified preparation of bacterial

protein obtained from β hemolytic streptococci.

It acts by forming a complex with

circulating plasminogen that binds loosely

to fibrin and it converts plasminogen to

plasmin. It has no intrinsic activity. It is

given by parenteral route and has a short

plasma half life.