Comparison of Unfractionated Heparin and Low-Molecular-Weight Heparin (LMWH)
| Unfractionated heparin | LMWH | |
|---|---|---|
| Route of administration | Intravenous | Sub-cutaneous |
| Time to peak action | Immediate onset Time to peak action 2–4h | 3–5h |
| Half-life | 45 min–1h | 2h |
| Metabolism/excretion | Metabolized in reticulo-endothelial system and liver | Metabolized in the liver and excreted by the kidney (approx. 40% renal clearance) |
| Advantages | More rapid offset may be safer peri-operatively and in bleeding | Wider therapeutic window; therefore does not require monitoring Easier to administer on outpatient basis |
| Disadvantages | Narrow therapeutic window necessitating monitoring Higher risk of HIT* | Longer half-life |
| Dose adjustments in renal impairment | Nil required | If CrCl <30 mL/min, monitor anti-Xa levels and adjust dose accordingly |
| Monitoring | 1.5–2.5× mid point of normal APTT range or anti-Xa levels if abnormal baseline APTT | Anti-Xa levels: only in severe renal impairment, extremes of body weight, if clot extension occurs while on treatment |
* HIT, heparin induced thrombocytopenia.