Past Papers · SAQ
Heparin vs Enoxaparin
2026B Q20
Exam questionCompare and contrast the pharmacology of unfractionated heparin and low molecular weight heparin using the following headings:
a) Mechanism(s) of action (20% of marks)
b) Pharmacokinetics (40% of marks)
c) Reversal with protamine (20% of marks)
d) Methods and requirement for monitoring (20% of marks)
CICMWrecks answer
Master answer
Heparin
- Binds to, and stabilizes anti-thrombin 3-thrombin complex
- → Potentiates the degradation of thrombin (does not occur with LMW heparins)
- Also aids antithrombin 3 degradation of factors IX and X (major function of LMW heparins)
| HEPARIN | ENOXAPARIN | ||
|---|---|---|---|
| PK | A | Subcut or IV administration | Subcut administration |
| ~90% bioavailability SC due to tissue binding | >95% bioavailability SC – NOT bound in tissues | ||
| D | 5% protein bound | 5% protein bound | |
| Vd – 0.3l/kg | Vd – 0.3l/kg | ||
| M | Heparinases | Minimal metabolism | |
| E | Renal elimination of inactive metabolites | Renal elimination of unchanged drug Dosage adjustment required in renal failure | |
| T1/2b ~2 hours | T1/2b 4~6 hours | ||
| Monitoring | APTT, activated clotting time | Anti-Xa assay (expensive, time-consuming) | |
| Adverse Effects | Bleeding | Bleeding | |
| Heparin induced thrombocytopoenia | Less likely to develop HITS | ||
| Osteoporosis | Less likely to develop Osteoporosis | ||
| Reversal | Reversal with protamine sulfate | Partial reversal with protamine sulfate (anti-Xa effect only ~60% neutralised) | |
Sakurai 2016
Quick reference
Summary
| UFH | LMWH | |
|---|---|---|
| MOA | Antithrombin potentiation; inhibits IIa and Xa (plus IXa/XIa/XIIa) | Antithrombin potentiation with anti-Xa predominance over anti-IIa |
| PK | Variable protein/endothelial binding; short dose-dependent t½ ~60–90 min; saturable cellular clearance plus renal component | High SC bioavailability, more predictable response, t½ ~4–6 h; predominantly renal clearance |
| Protamine | Near-complete reversal; dose guided by recent UFH exposure | Partial reversal; anti-Xa activity only ~60% neutralised |
| Monitoring | aPTT or anti-Xa; ACT for high-dose procedural use | Usually no routine monitoring; anti-Xa in selected patients such as severe renal dysfunction, pregnancy or extremes of body size |
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2026B Q20 | Compare and contrast the pharmacology of unfractionated heparin and low molecular weight heparin using the following headings: a) Mechanism(s) of action (20% of marks) b) Pharmacokinetics (40% of marks) c) Reversal with protamine (20% of marks) d) Methods and requirement for monitoring (20% of marks) | — |
| 2008A Q02 | Outline the differences between heparin and enoxaparin with respect to: a. Phamacokinetics b. Monitoring of effect c. Adverse effects d. Reversal of effect | 33% |