What is the initial heparin (unfractionated heparin (UFH) or low molecular weight heparin (LMWH)) dose for an adult patient with Deep Vein Thrombosis (DVT) and no significant renal impairment or history of bleeding disorders?

Heparin Dosing for DVT

For an adult patient with confirmed DVT and no renal impairment, initiate low-molecular-weight heparin (LMWH) at weight-based dosing: enoxaparin 1 mg/kg subcutaneously every 12 hours (or 1.5 mg/kg once daily) or dalteparin 200 U/kg once daily, as LMWH is preferred over unfractionated heparin for superior outcomes. 1, 2

Preferred Initial Anticoagulation Strategy

LMWH is the first-line choice over unfractionated heparin (UFH) for DVT treatment based on guideline recommendations (grade 2C evidence). 1 The American College of Chest Physicians guidelines specifically state that LMWH or fondaparinux should be preferred over UFH when bridging to warfarin. 1

LMWH Dosing Options

• Enoxaparin: 1 mg/kg subcutaneously every 12 hours OR 1.5 mg/kg once daily 1, 3
• Dalteparin: 200 U/kg subcutaneously once daily 1
• No routine anti-Xa monitoring required for most patients on standard weight-based LMWH dosing 3

Advantages of LMWH Over UFH

• Reduced mortality and major bleeding compared to UFH during initial DVT treatment 2, 3
• Lower risk of heparin-induced thrombocytopenia (HIT): UFH carries up to 5% HIT risk versus lower rates with LMWH 1
• More predictable pharmacokinetics: LMWH demonstrates better correlation between dose and anticoagulant effect (r=0.59) compared to UFH (r=0.38) 4
• Outpatient treatment feasibility with equivalent safety and efficacy to inpatient UFH therapy 3

Unfractionated Heparin Dosing (When LMWH Contraindicated)

If UFH is necessary (e.g., severe renal impairment with CrCl <30 mL/min), use the following FDA-approved weight-based protocol: 5

Intravenous UFH Protocol

• Initial bolus: 80 units/kg IV 1, 5
• Continuous infusion: 18 units/kg/hour 1, 5
• Target aPTT: 1.5-2.5 times control (corresponding to anti-Factor Xa level 0.3-0.7 IU/mL) 1, 5
• Monitoring frequency: Check aPTT every 4 hours initially, then at appropriate intervals after achieving therapeutic range 5

Subcutaneous UFH Alternative

• Initial dose: 333 units/kg subcutaneously 1
• Maintenance: 250 units/kg subcutaneously every 12 hours 1
• This regimen demonstrated equivalent safety and efficacy to IV UFH in the FIDO trial 1

Critical Safety Monitoring

Platelet Count Surveillance for HIT

• Monitor platelets every 2-3 days from day 4 to day 14 in patients receiving any heparin formulation with HIT risk ≥1% 1, 3
• HIT typically presents with ≥50% platelet decline 5-10 days after heparin initiation (earlier with prior exposure) 1
• Risk is substantially higher with UFH (up to 5%) compared to LMWH, particularly in post-orthopedic surgery patients 1

Additional Laboratory Monitoring

• Baseline assessment: aPTT, INR, platelet count, hematocrit 5
• Ongoing surveillance: Periodic hematocrit and occult blood in stool throughout therapy 5

Renal Impairment Considerations

LMWH accumulation occurs with CrCl <30 mL/min, requiring either: 1, 3

• Dose adjustment of LMWH with anti-Xa monitoring, OR
• Switch to UFH as the preferred alternative since it does not accumulate in renal failure 2, 3
• Contraindication: Fondaparinux is absolutely contraindicated if CrCl <30 mL/min 1

Transition to Oral Anticoagulation

• Initiate warfarin on the same day as starting parenteral anticoagulation 2
• Continue LMWH for minimum 5 days AND until INR 2.0-3.0 for at least 24 hours 2
• Target INR: 2.5 (range 2.0-3.0) 2
• When stopping heparin: No tapering required; discontinue UFH infusion completely before starting LMWH if transitioning between agents 3

Common Pitfalls to Avoid

• Do NOT use intramuscular route due to frequent hematoma formation 5
• Avoid inadequate initial anticoagulation: Failure to achieve aPTT >1.5 times control with UFH is associated with 25% risk of recurrent VTE 6
• Do NOT confuse heparin vial strengths: Verify correct concentration to prevent dosing errors, particularly avoiding confusion with catheter lock flush vials 5
• Ensure proper subcutaneous injection technique: Use deep subcutaneous (intrafat) injection above iliac crest or abdominal fat layer with 25-26 gauge needle 5