What is the recommended dose of aspirin (acetylsalicylic acid) for Deep Vein Thrombosis (DVT) prophylaxis in patients undergoing hip replacement surgery?

Aspirin Dosing for DVT Prophylaxis After Hip Replacement Surgery

The recommended dose of aspirin for DVT prophylaxis in hip replacement surgery is 81-162 mg daily, as higher doses (325 mg twice daily) have not demonstrated superior efficacy but may increase bleeding risk. 1, 2

Evidence-Based Recommendations

Aspirin Dosing

• Low-dose aspirin (81-162 mg daily) is effective for DVT prophylaxis following hip replacement surgery 1
• The Pulmonary Embolism Prevention (PEP) trial demonstrated that 160 mg daily aspirin reduced pulmonary embolism by 43% and symptomatic DVT by 29% in hip fracture patients 3
• Recent studies show no significant difference in VTE prevention between low-dose (81 mg twice daily) and regular-dose (325 mg twice daily) aspirin regimens 1

Duration of Therapy

• Aspirin should be started on the day of surgery and continued for 35 days 3, 4
• The AAOS guidelines suggest aspirin 325 mg twice daily (reducible to 81 mg daily if gastrointestinal symptoms develop) for 6 weeks, though evidence supports lower doses 4

Efficacy Considerations

• Aspirin alone reduces the risk of VTE by at least one-third during the period of increased risk 3
• A 2021 study found that even 75 mg daily aspirin was effective for VTE prophylaxis with no statistically significant difference in complication rates compared to LMWH 5

Important Caveats and Limitations

Guidelines Divergence

• The American College of Chest Physicians (ACCP) recommends DOACs over aspirin for DVT prophylaxis in hip fracture patients 2
• The ACCP does not recommend aspirin as the sole therapy for hip fracture surgery patients 4

Adjunctive Measures

• Mechanical prophylaxis (compression stockings or intermittent pneumatic compression devices) should be used as adjuncts to pharmacological prophylaxis 2
• Early mobilization and regional anesthesia provide additional DVT risk reduction 2

Alternative Pharmacological Options

• LMWH, fondaparinux, and rivaroxaban are alternative options with specific dosing recommendations:
  • LMWH: 10-14 days, extendable to 35 days
  • Rivaroxaban: 10 mg once daily, starting 6-10 hours after surgery
  • Fondaparinux: 2.5 mg once daily for 5-9 days, extendable up to 24 additional days 2

Special Patient Considerations

• For patients with high bleeding risk, aspirin may be preferred due to its lower bleeding risk profile compared to other anticoagulants 4
• For patients with renal impairment (CrCl <30 mL/min), aspirin may be a safer option than LMWH or fondaparinux 2
• Patients already taking aspirin for cardiovascular disease can continue their regular dose (as low as 75 mg) without additional thromboprophylaxis 5

Practical Implementation

1. Assess patient's bleeding risk and renal function
2. For standard-risk patients: Aspirin 81-162 mg daily, starting day of surgery
3. Continue for 35 days post-surgery
4. Combine with mechanical prophylaxis and early mobilization
5. Monitor for signs of bleeding or thrombosis during follow-up

The evidence suggests that low-dose aspirin (81-162 mg daily) provides effective DVT prophylaxis with a favorable safety profile for hip replacement patients, though other pharmacological options may be considered based on individual patient factors and institutional protocols.