Protocol for Initiating and Managing Heparin Therapy
For intravenous unfractionated heparin therapy, initiate with a weight-based bolus of 80 U/kg followed by a continuous infusion at 18 U/kg/hour, with dose adjustments based on aPTT measured 6 hours after initiation and following any dose changes. 1
Initial Dosing Protocol
Intravenous Unfractionated Heparin
- Initial bolus dose: 80 U/kg IV
- Initial continuous infusion: 18 U/kg/hour
- First aPTT measurement: 6 hours after bolus dose
- Target aPTT: 1.5-2.3 times control (typically 46-70 seconds)
Weight-Based Dose Adjustment Protocol 1
| aPTT (seconds) | Action |
|---|---|
| <35 (<1.2× control) | 80 U/kg bolus, then increase infusion by 4 U/kg/h |
| 35-45 (1.2-1.5× control) | 40 U/kg bolus, then increase infusion by 2 U/kg/h |
| 46-70 (1.5-2.3× control) | No change (therapeutic range) |
| 71-90 (2.3-3× control) | Decrease infusion rate by 2 U/kg/h |
| >90 (>3× control) | Stop infusion for 1 hour, then decrease rate by 3 U/kg/h |
Monitoring Protocol
- Check aPTT 6 hours after starting therapy or after any dose change
- Once therapeutic, check aPTT daily
- Monitor platelet count every 2-3 days for first 14 days, then every 2 weeks thereafter 1
- Periodically monitor hematocrit and check for occult blood in stool 2
Special Considerations
Alternative Subcutaneous Dosing
For patients who cannot receive IV therapy, subcutaneous administration can be used:
- Initial dose: 333 IU/kg followed by 250 IU/kg twice daily 3
- Or 5,000 units IV bolus followed by 15,000-20,000 units subcutaneously every 12 hours 2
Transitioning to Oral Anticoagulants
- Start oral anticoagulant (e.g., warfarin) within 24 hours of heparin initiation
- Continue full-dose heparin for at least 5 days
- Continue heparin until INR is therapeutic (2.0-3.0) for at least 2 consecutive days 1
- Allow at least 5 hours after the last IV heparin dose before drawing blood for INR 4
Special Patient Populations
Renal Dysfunction
- Standard unfractionated heparin is preferred over LMWH in severe renal failure (creatinine clearance <30 mL/min) 1
- More frequent monitoring may be needed as renal function deteriorates
Morbid Obesity
- Standard weight-based protocols with maximum doses may lead to significant delays in achieving therapeutic anticoagulation
- Consider using adjusted dosing weight: IBW + 0.3(actual weight - IBW) 5
- Higher initial doses and more aggressive dose adjustments may be needed
Cancer Patients
- For cancer patients with VTE, LMWH is generally preferred over unfractionated heparin for long-term therapy 1
- If unfractionated heparin is used, follow standard weight-based protocols
Complications and Management
Heparin-Induced Thrombocytopenia (HIT)
If HIT is suspected:
- Immediately discontinue all heparin products
- Switch to a direct thrombin inhibitor (e.g., lepirudin 0.4 mg/kg bolus followed by 0.15 mg/kg/h) 1
- Do not use warfarin alone in acute HIT as it may aggravate thrombosis
- Monitor platelet count recovery before transitioning to other anticoagulants
Bleeding Complications
- For minor bleeding: Consider dose reduction
- For major bleeding: Stop heparin infusion, consider protamine sulfate (1 mg per 100 units of heparin given in the previous 2-3 hours)
- Resume at lower dose once bleeding is controlled if anticoagulation still indicated
Common Pitfalls to Avoid
- Inadequate initial dosing: Underdosing leads to delayed therapeutic effect and increased risk of recurrent thromboembolism
- Delayed monitoring: Failure to check aPTT at 6 hours may result in prolonged subtherapeutic or supratherapeutic anticoagulation
- Fixed-dose protocols: Non-weight-based protocols often lead to suboptimal anticoagulation, especially in obese patients
- Failure to recognize heparin resistance: Some patients require higher doses due to increased heparin binding proteins
- Overlooking drug interactions: Medications that affect platelet function can increase bleeding risk when combined with heparin
By following this structured protocol for heparin initiation and management, clinicians can optimize anticoagulation therapy while minimizing risks of thrombosis and bleeding complications.