Within what time frame after surgery is pharmacologic DVT prophylaxis typically started?

• A. Before surgery.
• B. Within 12–24 hours postoperatively.
• C. Only after 72 hours.
• D. Not given.

Answer: (B)

Starting pharmacologic DVT prophylaxis within 12 to 24 hours after surgery reflects balancing two goals: preventing clot formation in a high-risk period after orthopedic procedures, while avoiding excessive bleeding at the surgical site while healing. After joint replacement or similar operations, clot risk is high, but giving anticoagulants too early can worsen postoperative bleeding. Initiating treatment within the first day provides timely protection against venous thromboembolism without substantially increasing bleeding risk. Beginning before surgery isn’t typical because anticoagulation during the operation can raise bleeding, and waiting until 72 hours or later leaves a window where clots can form. Prophylaxis is not given only if there are strong contraindications, such as active bleeding or significant coagulopathy.