ANTICOAGULANT

Definition of Anticoagulation

• Therapeutic interference ("blood-thinning") with the clotting mechanism of the blood to prevent or treat thrombosis and embolism.

Indications of Anticoagulant Therapy

• Treatment and Prevention of Deep Venous Thrombosis

• Pulmonary Emboli• Prevention of stroke in patients with atrial fibrillation,

artificial heart valves, cardiac thrombus.• During procedures such as cardiac catheterisation

Enhances Antithrombin Activity

Standard Heparin• Heterogeneous mixture of polysaccharide chains• MW 3k to 30k • Active in vitro and in vivo• Administration - parenteral- Do not inject IM - only IV

or deep s.c. • Half-life 1 - 2 hrs - monitor APTT (activated partial

thromboplastin time)• Adverse effect - haemorrhage – • antidote - protamine sulphate

Heparin mechanism of action

Heparin

Antithrombin III Thrombin

Monitoring Heparin

• Activated Partial Thromboplastin Time (APTT)• Normal range: 25-40 seconds • Therapeutic Range: 55-70 seconds

Low Molecular Weight Heparin

• Changed management of venous thromboembolism

• Standard (Unfractionated) heparin 30k• LMWH contains polysaccharide chains MW 5k• Enriched with short chains with higher anti-

Xa:IIa ratio

Differences in Mechanism of Action

• Any size of heparin chain can inhibit the action of factor Xa by binding to antithrombin (AT)

• In contrast, in order to inactivate thrombin (IIa), the heparin molecule must be long enough to bind both antithrombin and thrombin

• the chains of LMWH are not long enough to bind antithrombin and thrombin

Complications of Heparin

• Hemorrhage(can be reversed by using protamine sulfate as an antidote)

• Heparin-induced thrombocytopenia (HIT) and thrombosis

• Osteoporosis (long-term only) more than 6 month; the explanation of this side effect is unknown

• Hyperkalemia • Hypersensitivity reaction

Heparin-Induced Thrombocytopaenia

• Most significant adverse effect of heparin after haemorrhage

• Most common drug-induced thrombocytopenia

Major adverse effects of heparin

Trreatment of HIT

• Discontinue all heparin• If need to continue anti-coagulation, use

danaparoid (orgaran).• Avoid platelet transfusions• Thrombosis: use danaparoid or thrombin

inhibitor(Hirudin)

Oral anticoagulant • Warfarin is an oral anticoagulant that prevent

thrombosis• It inhibit the enzymatic reduction of vitamin K

to its hydroquinone form, interfering with the post translational modification (carboxylation) of glutamic acid residues in clotting factors 2, 9, 7, 10.

• Warfarin acts only in vivo

Vitamin K

Synthesis of Functional

Coagulation Factors

VII

IX

X

II

Vitamin K-Dependent Clotting Factors

Warfarin

Synthesis of Non Functional

Coagulation Factors

Antagonismof

Vitamin K

Warfarin Mechanism of Action

Vitamin K

VII

IX

X

II

Warfarin

Side effects of warfarin • Bleeding• Hepatotoxicity • Warfarin induced skin necrosis(can be reduced

by starting heparin and warfarin concomitantly)

Warfarin: Major Adverse Effect—Haemorrhage

• Factors that may influence bleeding risk:– Intensity of anticoagulation– Concomitant clinical disorders(liver disease ,thyrotoxicosis and fever )– Concomitant use of other medications1. Cimetidine and other enzyme inhibitors increase its action while

rifampicin and other enzyme inducers inhibit the action of warfarin 2. aspirin increase its bleeding risk by working in synergistic

fashion(PLATELETS INHIBITION) .3. NSAIDS and chloral hydrate displace it from binding sites4. Antibiotic eliminate the intestinal flora that produce vitamin k this

will increase the risk of bleeding – Quality of management

Prothrombin Time (PT)• Historically, a most reliable and “relied upon” clinical

testHowever:

– Proliferation of thromboplastin reagents with widely varying sensitivities to reduced levels of vitamin K-dependent clotting factors has occurred

– Problem addressed by use of INR (International Normalized Ratio)

Changing over from Heparin to Warfarin

• May begin concomitantly with heparin therapy• Heparin should be continued for a minimum of four

days– Time to peak antithrombotic effect of warfarin is

delayed 96 hours (despite INR)• When INR reaches desired therapeutic range,

discontinue heparin (after a minimum of four days)

Warfarin: Dosing & Monitoring• Start low

– Initiate 5 mg daily– Educate patient

• Stabilize– Titrate to appropriate INR – Monitor INR frequently (daily then weekly)

• Adjust as necessary• Monitor INR regularly (every 1–4 weeks) and adjust

Contraindications to Warfarin Therapy

• Pregnancy (it is a teratogenic drug can cause maxillofacial abnormality if given in the first trimester and increase the incidence of bleeding in the new born baby in the last trimester; but it can be given in the middle trimester of pregnancy but with higher doses to achieve the target INR because there is hyper-coaguability state during pregnancy

• Situations where the risk of hemorrhage is greater than the potential clinical benefits of therapy– Uncontrolled alcohol/drug abuse– Unsupervised dementia/psychosis

Signs of Warfarin Overdosage

• Any unusual bleeding:– Blood in stools or urine– Excessive menstrual bleeding– Bruising– Excessive nose bleeds/bleeding gums– Persistent oozing from superficial injuries– Bleeding from tumor, ulcer, or other lesion

Reversing action of warfarin

• Plasma(fresh frozen plasma or clotting factors)– Rapid but short-lasting, used mainly for life

threating bleeding • Vitamin K

– Not rapid, but lasts 1-2 weeks. Do not use if wishing to restart warfarin within next week.

In some cases only stopping the drug can be enough

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