What is the recommended dosing and monitoring protocol for a heparin (unfractionated heparin) drip?

Heparin Drip Dosing and Monitoring Protocol

For intravenous unfractionated heparin (UFH) therapy, the recommended dosing is an initial bolus of 80 U/kg followed by a continuous infusion at 18 U/kg/hour, with dose adjustments based on activated partial thromboplastin time (aPTT) monitoring to maintain a therapeutic range of 1.5-2.5 times control (approximately 46-70 seconds). 1

Initial Dosing

• Initial bolus: 80 U/kg IV
• Initial infusion rate: 18 U/kg/hour
• First aPTT measurement: 6 hours after initiation

Monitoring and Dose Adjustment Protocol

The following weight-based nomogram should be used for dose adjustments:

aPTT (seconds)	aPTT (× control)	Action
<35	<1.2	80 U/kg bolus, increase infusion by 4 U/kg/hour
35-45	1.2-1.5	40 U/kg bolus, increase infusion by 2 U/kg/hour
46-70	1.5-2.3	No change (therapeutic range)
71-90	2.3-3.0	Decrease infusion by 2 U/kg/hour
>90	>3.0	Stop infusion for 1 hour, then decrease by 3 U/kg/hour

1

Frequency of Monitoring

• Initial aPTT: 6 hours after starting therapy
• After dose adjustment: Repeat aPTT 6 hours later
• Once stable in therapeutic range: Daily monitoring

Target Therapeutic Range

• aPTT ratio of 1.5-2.5 times control
• This corresponds to heparin levels of 0.3-0.7 IU/mL by anti-factor Xa assay 1

Important Clinical Considerations

Heparin-Induced Thrombocytopenia (HIT) Monitoring

• Monitor platelet count every 2-3 days from day 4 to day 14 of therapy
• Risk of HIT with UFH may be as high as 5%, particularly in orthopedic surgery patients
• HIT typically presents as a ≥50% decline in platelet count within 5-10 days of starting heparin (earlier with previous exposure) 1

Special Populations

1. Morbidly obese patients:

   • Standard weight-based protocols with maximum initial doses may result in significant delays in achieving therapeutic anticoagulation
   • Consider using adjusted dosing weight formulas: IBW + 0.3(ABW - IBW) or IBW + 0.4(ABW - IBW) 2

2. Renal impairment:

   • UFH is preferred over LMWH in patients with CrCl <30 mL/min as it's primarily metabolized by the liver 1

3. Transitioning to oral anticoagulants:

   • Continue UFH for at least 5 days and until INR ≥2.0 for at least 24 hours when transitioning to warfarin 1, 3
   • Measure prothrombin time when heparin activity is low (about 5 hours after last IV bolus) 3

Common Pitfalls to Avoid

1. Inadequate initial dosing: Subtherapeutic aPTT values in the first 24-48 hours are associated with increased risk of recurrent thromboembolism (up to 15-fold higher risk) 1

2. Failure to validate aPTT ranges: Different aPTT reagents have varying sensitivities to heparin; institutions should validate their therapeutic ranges to correspond to heparin levels of 0.3-0.7 IU/mL 1

3. Overlooking drug interactions: Heparin efficacy can be affected by concurrent medications, particularly thrombolytics and platelet GP IIb/IIIa antagonists 1

4. Delayed recognition of heparin resistance: Some patients may require higher doses due to increased heparin binding to plasma proteins or elevated factor VIII levels 1

By following this evidence-based protocol for heparin administration and monitoring, clinicians can optimize anticoagulation therapy while minimizing risks of both thrombotic and bleeding complications.