heparins
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Updated 2026-03-25
Contents
heparins
Parenteral anticoagulants: UFH (antithrombin-mediated IIa + Xa inhibition), LMWH (predominantly anti-Xa), and fondaparinux (selective anti-Xa). UFH preferred when short half-life, reversibility, or renal-independent clearance is needed (ACS with planned PCI, haemodynamic instability, severe CKD). LMWH is the workhorse for VTE treatment, ACS, and bridging.
dosing
| Agent | Dose (common indications) | Monitoring |
|---|---|---|
| UFH — ACS | 60 U/kg bolus (max 4000 U) → 12 U/kg/h (max 1000 U/h) | aPTT 1.5–2.5× control (or anti-Xa 0.3–0.7) |
| UFH — VTE | 80 U/kg bolus → 18 U/kg/h | aPTT target per protocol |
| Enoxaparin — VTE treatment | 1 mg/kg BID or 1.5 mg/kg OD | anti-Xa if CrCl <30, obesity, pregnancy |
| Enoxaparin — ACS | 1 mg/kg BID (reduce to 1 mg/kg OD if CrCl <30) | — |
| Dalteparin — VTE (cancer) | 200 IU/kg OD × 30d → 150 IU/kg OD | — |
| Fondaparinux — VTE/ACS | 2.5 mg OD SC | none required; avoid if CrCl <20 |
fondaparinux in PCI
Fondaparinux must NOT be used as sole anticoagulant during PPCI — catheter thrombosis risk. Requires UFH bolus at time of PCI.
key points
- UFH advantages: short half-life (~1h), fully reversible with protamine, no renal clearance — preferred in ACS with planned PCI, haemodynamic instability, severe CKD, obesity (dose by weight with monitoring)
- LMWH advantages: predictable pharmacokinetics, SC dosing, no routine monitoring in most patients, lower HIT risk than UFH
- Fondaparinux: lowest HIT risk; useful in HIT history; avoid if CrCl <20; not suitable as sole agent during PCI
- HIT: UFH >> LMWH risk; use 4T score for pretest probability — if intermediate/high, stop all heparin, send anti-PF4 antibodies, start non-heparin anticoagulant (argatroban or bivalirudin)
reversal
| Agent | Reversal | Notes |
|---|---|---|
| UFH | protamine 1 mg per 100 U (max 50 mg) | give slowly — hypotension, anaphylaxis |
| LMWH | protamine (partial reversal ~60% anti-Xa) | less effective than for UFH |
| fondaparinux | no specific reversal; consider rFVIIa | long half-life (17h) |
adverse effects
- UFH: HIT (1–5%), osteoporosis with prolonged use
- LMWH: HIT (lower incidence), injection site reactions
- All: bleeding (dose-dependent)