Past Papers · SAQ

Anticoagulants — LMWH & Hirudin

Current · V5 (2025) → N4.i Historical · V4 (2023) → Q2.i 1 exam appearance

2011B Q04

Exam question

Describe the pharmacology of low molecular weight heparin (70% marks). Outline the pharmacology of hirudin (30% marks).

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Field LOW MOLECULAR WEIGHT HEPARIN (LMWH)
Haematology · Haematology · Level 1
HIRUDIN
Haematology · Haematology
Mechanism of action

Activates antithrombin but due to shorter length preferentially inhibits factor Xa

is via direct irreversible binding to thrombin Causes a prolongation of bleeding time

Absorption

up to 90% via SC (greater than heparin)

administered SC

Protein binding

less prot bind than heparin

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Volume of distribution

Vd ~ 0.1L/kg

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Metabolism

Hepatic depolymerisation and desulfation to less active fragments

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Excretion

urine as 40% of dose and 10% active fragments, dose adjustment in renal failure

excreted in the urine, dose adjustment
required in renal failure

Half-life

2-4 times longer half-life than heparin
dose independent half time

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Adverse Effects Toxicity

Bleeding
Needs adjustment in renal failure
Less HITS and osteoporosis

Bleeding

Class Group

Anticoagulants

Anticoagulants

Indications Uses

1. the prevention of venous thromboembolic disease
2. the treatment of acute coronary syndromes.

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Introduction

Enoxaparin is a LMWH prepared from
unfractionated heparin by controlled
enzymatic or chemical depolymerisation
Consists of smaller fragments of
Heparin. MW: Average of 5000 Daltons

Is a naturally occurring peptide found in leaches saliva with anticoagulant properties
recombinant techniques are used to create drugs in this class

Legacy Cicm Level

Level 1

Not in list
(Historical question)

Presentation

Usually s/c, but can be given i.v.
20mg or 40mg BD s/c as prophylaxis, 1mg/kg BD s/c as therapeutic dose

Monitor:
Anti-Xa level

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Special Points

Reversal:
Protamine by slow infusion
Less e¬ffective than heparin due to the preferential Xa action (1mg/1mg
LMWH), but max effect is < 60%

Reversal:
irreversible binding - no reversal agent
dialysis with PMMA membranes works

Past papers

Exam appearances

1 appearance
Exam Exact exam wording Candidate success
2011B Q04 Describe the pharmacology of low molecular weight heparin (70% marks). Outline the pharmacology of hirudin (30% marks). 40%