Table 5.
Characteristics of unfractionated heparin (UFH) vs. low molecular weight heparin (LMWH) and their management in patients undergoing non-cardiac surgery [1,24].
| Features | UFH | LMWH |
|---|---|---|
| Mean molecular weight | 15,000 Da | 5000 Da |
| Target | Xa and IIa | Xa and IIa (greater Xa inhibition than IIa) |
| Bioavailability (%) | 30 | 90 |
| Half-life | 1 h | 4 h |
| Renal Excretion | No | Yes |
| Antidote (Protamine sulfate) | Complete reversal | Partial reversal (~50%) |
| Heparin-induced thrombocytopenia (HIT) | <5% | <1% |
| Method of administration | Intravenous infusion or less frequently subcutaneously. | Subcutaneously (less frequently can be administered intravenously if a rapid anticoagulant response is needed). |
| Monitoring | aPTT | Not necessary (predictable anticoagulant response). |
| Dosages • Prophylaxis • Therapeutic |
- Usually given in fixed doses of 5000 units subcutaneously two or three times daily. * | - 4000 to 5000 units daily or 2500 to 3000 units twice daily subcutaneously. |
| - Initial bolus of 5000 U followed by 30,000 to 35,000 U/24 h followed by intravenous infusion with aPTT monitoring. | - Subcutaneously according to body weight (100 U/kg twice daily). - The dose needs to be reduced in patients with renal impairment (GFR < 30 mL/min/1.73 m2). |
|
| Management before non-cardiac surgery | - Discontinue administration ≥4 h before surgery. - Resume full dose ≥12 h after surgery. - In case of urgent/emergent surgery immediately discontinue. If needed, complete reversal with protamine sulphate. |
- Discontinue administration ≥12 h before surgery. - Resume full dose ≥12 h after surgery. - In case of urgent/emergent surgery immediately discontinue. If needed, partial reversal (~50%) with protamine sulphate. |
| Limitations | Dose-dependent clearance (binds to endothelial cells); variable anticoagulant response (binds to plasma proteins). | Potential accumulation in patients with renal insufficiency (GFR <30 mL/min/1.73 m2). |
| Side effects | - Short term: • bleeding (most common, increasing with higher heparin doses or concomitant administration of antiplatelet or fibrinolytic agents); • HIT (it occurs 5 to 14 days after the initiation of heparin therapy, but it may be manifested earlier if the patient has received heparin within the past 3 months); • elevated levels of transaminases (rapidly return to normal when the drug is stopped). - Long term: • osteoporosis. |
The same as UFH but less frequent. |
* Monitoring of coagulation is unnecessary.