Heparin Dosing for Pulmonary Embolism in Lung Cancer Patients
For a patient with lung cancer and pulmonary embolism, administer unfractionated heparin as an initial intravenous bolus of 80 IU/kg followed by continuous infusion at 18 IU/kg/hour, with dose adjustments based on aPTT monitoring to maintain levels at 1.5-2.5 times control (45-75 seconds). 1, 2
Initial Dosing Protocol
The weight-adjusted regimen is superior to fixed dosing and should be implemented immediately upon suspicion of PE, even before diagnostic confirmation is complete 1:
- Initial bolus: 80 IU/kg intravenous push 1, 3
- Maintenance infusion: 18 IU/kg/hour by continuous IV infusion 1, 3
- Target aPTT: 1.5-2.5 times control value (45-75 seconds) 1, 4, 2
The FDA-approved alternative standard dosing (5,000-10,000 unit bolus followed by 1,300 units/hour maintenance) is less optimal as it does not account for patient weight and may result in subtherapeutic anticoagulation 2.
Monitoring Schedule
Critical timing for aPTT checks 1, 2:
- First check: 4-6 hours after initial bolus
- After any dose adjustment: 6-10 hours later
- Once therapeutic: Daily monitoring
Dose Adjustment Algorithm
Use the following aPTT-based nomogram for infusion rate adjustments 1:
| aPTT Result | Action Required |
|---|---|
| <35 seconds (<1.2× control) | Give 80 IU/kg bolus; increase infusion by 4 IU/kg/hour |
| 35-45 seconds (1.2-1.5× control) | Give 40 IU/kg bolus; increase infusion by 2 IU/kg/hour |
| 46-70 seconds (1.5-2.3× control) | No change - therapeutic range |
| 71-90 seconds (2.3-3.0× control) | Reduce infusion by 2 IU/kg/hour |
| >90 seconds (>3.0× control) | Stop infusion for 1 hour, then reduce by 3 IU/kg/hour |
Special Considerations for Cancer Patients
Cancer patients have unique thrombotic risks that warrant specific attention 5:
- Cancer patients have substantially higher rates of recurrent thromboembolism (17% at 6 months) compared to non-cancer patients 5
- After initial heparin therapy (5-7 days), consider transitioning to extended low-molecular-weight heparin (dalteparin 200 IU/kg daily for 1 month, then 150 IU/kg daily for 5 months) rather than warfarin, as this reduces recurrent VTE risk by 52% without increasing bleeding 5
- The mortality benefit of anticoagulation in cancer patients is primarily through prevention of fatal recurrent PE, not through cancer treatment effects 5
Transition to Oral Anticoagulation
Overlap heparin with warfarin for adequate duration 1, 3, 2:
- Start warfarin 5-10 mg daily simultaneously with heparin 1, 3
- Continue heparin for minimum 5 days AND until INR ≥2.0 for at least 24 hours 1, 3
- Target INR: 2.0-3.0 1, 3
- Never discontinue heparin prematurely before achieving therapeutic INR 3, 6
Critical Safety Monitoring
Monitor for complications throughout therapy 2:
- Platelet count monitoring for heparin-induced thrombocytopenia (HIT) - check at baseline and periodically 1, 2
- Hematocrit monitoring 2
- Stool occult blood testing 2
Common Pitfalls to Avoid
Do not delay anticoagulation - Start heparin immediately when PE is suspected, even before diagnostic confirmation, as untreated PE carries high mortality 1, 3, 6
Avoid fixed-dose protocols - Weight-based dosing (80 IU/kg bolus, 18 IU/kg/hour) achieves therapeutic anticoagulation faster and more reliably than fixed dosing 1
Do not use subtherapeutic dosing - Failure to achieve aPTT >1.5× control within the first 24 hours is associated with a 25% risk of recurrent VTE 7
Avoid intramuscular administration - Use only intravenous or deep subcutaneous routes due to high risk of hematoma formation with IM injection 2
Do not stop heparin too early - Continue for minimum 5 days regardless of INR, as warfarin's full anticoagulant effect requires depletion of vitamin K-dependent clotting factors 1, 2