How it's calculated
The Raschke weight-based nomogram bolus and infusion rates are calculated directly from body weight — 80 units/kg bolus with an 18 units/kg/hr initial infusion for standard-intensity anticoagulation (e.g. VTE treatment), or 60 units/kg / 12 units/kg/hr for lower-intensity protocols sometimes used in acute coronary syndromes.
Typical aPTT-based titration (confirm against local protocol)
| aPTT result | Typical action |
|---|---|
| Below target range | Rebolus and/or increase infusion rate |
| Within target range | No change |
| Above target range | Hold infusion and/or decrease rate |
Clinical use
- Used for therapeutic anticoagulation in confirmed VTE, some ACS presentations, and mechanical valve/high-risk atrial fibrillation bridging, where rapid onset and easy reversibility (protamine) are valued.
- Requires regular aPTT (or anti-Xa) monitoring — typically 6 hours after the bolus and after every rate change — with dose titrated per a local nomogram.
- Preferred over LMWH in significant renal impairment, or where rapid reversal may be needed (e.g. pre-procedure, active bleeding risk).
Frequently asked questions
Why does heparin need such frequent monitoring compared to LMWH?
Unfractionated heparin has unpredictable, non-linear pharmacokinetics with significant inter-patient variability, so the dose-response relationship must be checked and titrated regularly via aPTT or anti-Xa levels — LMWH's more predictable clearance generally doesn't require routine monitoring at standard doses.
What's the advantage of heparin over LMWH?
Heparin's short half-life and full reversibility with protamine make it preferable when rapid anticoagulation reversal might be needed (e.g. peri-procedurally, active bleeding risk, or significant renal impairment where LMWH accumulates).
Why do ACS protocols sometimes use a lower-intensity regimen?
Lower-intensity heparin (60 units/kg bolus, 12 units/kg/hr) is used in some acute coronary syndrome protocols, particularly alongside fibrinolytics or antiplatelet therapy, to balance anticoagulation benefit against bleeding risk — always confirm the intended intensity against your institution's specific protocol.
References
- Raschke RA, et al. The weight-based heparin dosing nomogram compared with a standard care nomogram. Ann Intern Med. 1993;119(9):874-881.
- Garcia DA, et al. Parenteral Anticoagulants: ACCP Guidelines. Chest. 2012.