What is the recommended dose of heparin (unfractionated heparin) for deep vein thrombosis (DVT) prophylaxis in an adult patient?

Heparin DVT Prophylaxis Dosing

For DVT prophylaxis in adult patients, unfractionated heparin should be administered at 5,000 units subcutaneously every 8 hours, as this three-times-daily regimen provides superior protection compared to twice-daily dosing. 1

Standard Prophylactic Regimen

The recommended dose is 5,000 units subcutaneously every 8 hours for most hospitalized patients requiring VTE prophylaxis. 2, 1

• This TID (three-times-daily) dosing provides more consistent anticoagulant effect and greater reduction in DVT incidence compared to BID (twice-daily) administration 1, 3
• The every-8-hour regimen is specifically recommended by the American Heart Association and is the standard in current guidelines 1
• For cancer patients, 5,000 units every 8 hours is explicitly the preferred regimen given their elevated thrombotic risk 2, 1, 4

Alternative Dosing for Moderate-Risk Patients

• 5,000 units subcutaneously every 12 hours is acceptable for moderate-risk medical patients but provides less robust protection than TID dosing 2, 1, 3
• This BID regimen may be appropriate when bleeding risk is elevated or for patients with fewer VTE risk factors 3

Timing and Duration

Initiate heparin 2 hours before surgery for surgical patients to achieve adequate anticoagulation at the time of greatest thrombotic risk 5, 6

• Continue prophylaxis for at least 7-10 days postoperatively or until the patient is fully ambulatory, whichever is longer 2, 5
• For cancer patients undergoing major abdominal or pelvic surgery, consider extended prophylaxis up to 35 days given persistently elevated thrombotic risk 2, 3
• Medical patients should receive prophylaxis throughout hospitalization until fully ambulatory 2, 4

Special Population Adjustments

Renal Impairment

• UFH is the preferred agent when creatinine clearance is <30 mL/min as it is primarily metabolized by the liver rather than renally excreted 1, 4, 3
• Standard dosing of 5,000 units every 8 hours can be used without dose adjustment in renal failure 1

Low Body Weight Patients (≤50 kg)

• Consider reduced-dose prophylaxis: 5,000 units every 12 hours in critically ill patients weighing ≤50 kg 7
• This reduced dosing strategy is associated with lower bleeding risk (5% vs 12.5%) while maintaining similar VTE protection 7

Obese Patients

• Standard dosing of 5,000 units every 8 hours remains appropriate for obese patients 8
• Higher doses (7,500 units every 8 hours) have not demonstrated clear benefit and may increase bleeding risk 8

Evidence Comparing BID vs TID Dosing

TID dosing (every 8 hours) is superior to BID dosing (every 12 hours) for preventing clinically significant VTE events. 9

• Meta-analysis shows TID heparin demonstrates a trend toward decreased pulmonary embolism (BID 1.5 vs TID 0.5 per 1,000 patient-days, p=0.09) 9
• TID dosing reduces proximal DVT and PE combined (BID 2.3 vs TID 0.9 per 1,000 patient-days, p=0.05) 9
• However, TID dosing carries increased major bleeding risk (BID 0.35 vs TID 0.96 per 1,000 patient-days, p<0.001) 9

Critical Pitfalls to Avoid

Do not use UFH in patients with active or history of heparin-induced thrombocytopenia (HIT) - use a direct thrombin inhibitor or fondaparinux instead 1

• Monitor platelet counts every 2-3 days from day 4 to day 14 in patients with HIT risk ≥1% 1
• Avoid administering anticoagulants within 10-12 hours of neuraxial anesthesia due to spinal hematoma risk 1, 4
• Do not default to BID dosing for high-risk patients (≥2 VTE risk factors, weight >100 kg, cancer patients) as this provides subtherapeutic prophylaxis 3
• Absolute contraindications include active major bleeding, recent CNS hemorrhage, or high-risk intracranial/spinal lesions 3

When UFH is Preferred Over LMWH

• Severe renal impairment (CrCl <30 mL/min) where LMWH accumulates and increases bleeding risk 1, 4, 3
• Need for rapid reversibility with protamine sulfate 1
• Cost considerations in resource-limited settings 1
• History of LMWH-associated adverse reactions 1

High Bleeding Risk Patients

For patients at high risk for bleeding, use mechanical thromboprophylaxis (graduated compression stockings and/or intermittent pneumatic compression) until bleeding risk diminishes, then initiate pharmacologic prophylaxis 2, 3