What is the recommended subcutaneous unfractionated heparin dose and schedule for deep‑vein thrombosis prophylaxis in an adult older than 75 years?

Heparin Dosing for DVT Prophylaxis in Patients Over 75 Years

For adults over 75 years requiring DVT prophylaxis, administer unfractionated heparin 5,000 units subcutaneously every 8 hours, which is the standard prophylactic regimen regardless of age. 1

Standard Prophylactic Dosing

• The recommended dose is 5,000 units subcutaneously every 8 hours (three times daily), which provides superior DVT prevention compared to twice-daily dosing. 1, 2
• The three-times-daily regimen is specifically endorsed for cancer patients and surgical patients, and maintains more consistent anticoagulant levels throughout the day. 1, 2, 3
• Twice-daily dosing (5,000 units every 12 hours) is less effective and should be avoided when optimal prophylaxis is needed. 3

Age-Specific Considerations for Patients Over 75 Years

• No dose reduction is required based solely on age over 75 years. 4
• The FDA label states that "patients over 60 years of age may require lower doses of heparin," but this is a general statement without specific dosing recommendations, and guideline evidence supports standard dosing. 4
• Older patients may have higher serum heparin levels and longer aPTT compared to younger patients, but prophylactic dosing does not require aPTT monitoring. 1

Critical Monitoring Requirements

• Check platelet counts every 2-3 days from day 4 through day 14 to screen for heparin-induced thrombocytopenia (HIT). 1, 5
• Monitor hemoglobin, hematocrit, and signs of bleeding throughout therapy. 1
• If platelets fall below 50 × 10⁹/L, strongly consider discontinuing prophylactic anticoagulation. 5

Duration and Timing

• Initiate prophylaxis 2 hours before surgery for surgical patients to achieve adequate anticoagulation at the time of greatest thrombotic risk. 2, 6, 4
• Continue for at least 7-10 days postoperatively or until the patient is fully ambulatory, whichever is longer. 1, 2, 4
• For medical patients, continue prophylaxis throughout hospitalization until fully ambulatory. 1, 2

Special Circumstances in Elderly Patients

Renal Impairment

• Unfractionated heparin is the preferred agent when creatinine clearance is <30 mL/min, as it is primarily metabolized by the liver rather than renally excreted. 1, 2, 6
• Standard dosing of 5,000 units every 8 hours can be used without dose adjustment in renal failure. 5, 6

Bleeding Risk Assessment

• Fondaparinux should be used with caution in patients >75 years with moderate renal insufficiency (CrCl 30-50 mL/min), weight <50 kg, or age >75 years. 1
• For elderly patients at high bleeding risk, mechanical prophylaxis (graduated compression stockings and/or intermittent pneumatic compression) should be used until bleeding risk diminishes. 1

Critical Pitfalls to Avoid

• Do not confuse prophylactic dosing (5,000 units every 8 hours) with therapeutic dosing (80 U/kg bolus followed by 18 U/kg/hour infusion), which requires aPTT monitoring. 1, 6
• Avoid administering anticoagulants within 10-12 hours of neuraxial anesthesia due to spinal hematoma risk. 5, 6
• Do not use unfractionated heparin in patients with active or history of heparin-induced thrombocytopenia; use a direct thrombin inhibitor or fondaparinux instead. 5
• Do not reduce the dose to 5,000 units twice daily in elderly patients, as this provides inadequate prophylaxis. 3

Alternative Agents (When UFH is Contraindicated)

• Enoxaparin 40 mg subcutaneously once daily is an alternative, but requires dose reduction to 30 mg once daily if CrCl <30 mL/min. 1, 2
• Dalteparin 5,000 IU subcutaneously once daily is another option. 1
• Fondaparinux 2.5 mg subcutaneously once daily, but use with extreme caution in patients >75 years with renal impairment. 1