Heparin Dose for DVT Prophylaxis
For DVT prophylaxis in patients with normal renal function and weight between 40-100 kg, administer unfractionated heparin 5,000 units subcutaneously every 8 hours. 1, 2
Standard Dosing Regimen
The recommended dose is 5,000 units subcutaneously every 8 hours (three times daily), which is superior to twice-daily dosing. 3, 1, 2
- Three-times-daily dosing provides more consistent anticoagulant effect and greater reduction in DVT incidence compared to every 12-hour dosing 1, 2
- The American Heart Association specifically recommends 5,000 units every 8 hours as the standard prophylactic regimen 1
- While 5,000 units every 12 hours is acceptable for moderate-risk medical patients, it provides less robust protection 1
Patient Population Specifics
General Medical Patients
- For acutely ill hospitalized patients, use 5,000 units subcutaneously every 8 hours throughout hospitalization 3
- Continue prophylaxis until the patient is fully ambulatory 3, 4
Surgical Patients
- Initiate 5,000 units subcutaneously every 8 hours, starting 2 hours before surgery 1
- Continue for at least 7-10 days postoperatively or until fully ambulatory, whichever is longer 1, 4
Cancer Patients
- Use 5,000 units subcutaneously every 8 hours specifically for cancer patients 3, 1, 4, 2
- Consider extended prophylaxis beyond 10 days for cancer patients undergoing major abdominal or pelvic surgery 1
Heart Failure Patients
- For hospitalized patients with congestive heart failure, use 5,000 units subcutaneously every 8 hours 3, 5
- Enoxaparin 40 mg subcutaneously daily is an acceptable alternative 3, 5
Critical Clinical Pitfalls to Avoid
Do NOT Use Twice-Daily Dosing in High-Risk Patients
- Avoid 5,000 units every 12 hours in surgical patients and cancer patients—it is less effective 1, 2
- Meta-analysis shows twice-daily dosing provides less reduction in proximal DVT and pulmonary embolism 2
Contraindications and Monitoring
- Never use UFH in patients with active or history of heparin-induced thrombocytopenia (HIT)—use fondaparinux or a direct thrombin inhibitor instead 1, 2
- Monitor platelet counts every 2-3 days from day 4 to day 14 in patients with HIT risk ≥1% 1, 2
- Avoid administering within 10-12 hours of neuraxial anesthesia due to spinal hematoma risk 1, 4
Do NOT Routinely Monitor Anti-Xa Levels
- Routine monitoring of anti-Xa levels is unnecessary for prophylactic dosing 4, 2
- Monitoring may be considered only in patients with extreme body weights or renal impairment 4
When UFH is Preferred Over Low Molecular Weight Heparin
UFH is the agent of choice in the following situations:
- Severe renal impairment (creatinine clearance <30 mL/min)—UFH is primarily metabolized by the liver, not renally excreted 1, 4, 2
- Standard dosing of 5,000 units every 8 hours can be used without dose adjustment in renal failure 1, 2
- Cost considerations in resource-limited settings 1
- History of LMWH-associated adverse reactions 1
Special Consideration: Obesity
Do NOT increase the dose to 7,500 units every 8 hours in obese patients weighing >100 kg—this increases bleeding risk without reducing VTE incidence. 6
- A 2016 study demonstrated that high-dose UFH (7,500 units every 8 hours) in patients >100 kg resulted in significantly higher bleeding complications without additional VTE protection 6
- Patients in obese class III receiving high-dose heparin had 11% transfusion rate versus 5% with standard dosing (p<0.01) 6
- Maintain 5,000 units every 8 hours even in obese patients; consider LMWH with weight-based dosing as an alternative 4, 6