ACE-CAA Issue 4 Sample Question

Tranexamic acid (TXA) inhibits the action of which of the following?

A. Thrombin X

B. Fibrinogen X

C. Plasmin ✔

Read the discussion below.

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Discussion

Tranexamic acid (TXA) is an antifibrinolytic agent that inhibits the action of plasmin and plasminogen. TXA inhibits fibrinolysis by competitively binding to the lysine receptor domains on plasmin and plasminogen, thereby preventing their binding to fibrin (Figure 1). This stabilizes clots and prevents the clot breakdown that can exacerbate bleeding.

Figure 1. Mechanism of action of the lysine analogue, tranexamic acid (TXA). TXA blocks the lysine binding sites in plasmin. © 2022 American Society of Anesthesiologists.

TXA was originally approved for the management of medical bleeding in patients with hemophilia and menorrhagia. The use of TXA in cardiac surgery has grown significantly in recent years, as has its use in noncardiac surgery, especially in orthopedic surgery, reconstructive spine surgery, obstetrics, and trauma. It is also used in otolaryngology surgery. 

The World Health Organization recommends the use of TXA within 3 hours of birth, in addition to standard of care management for postpartum hemorrhage following cesarean or vaginal delivery. In trauma patients, it is typically administered as a loading dose followed by an infusion. The protocols for orthopedic surgery are much more variable.

Theoretically, the use of TXA can promote thromboembolic events; however, large clinical trials in hospitals have not shown this effect to be clinically significant. Seizures are a recognized, though rare, adverse effect of TXA administration. This effect has been encountered in patients undergoing cardiac surgery.

Since TXA is cleared by the kidney, it accumulates with falling glomerular filtration rate and its dose may need to be adjusted in patients with renal dysfunction.

TXA does not affect the function of thrombin, and blocking the function of thrombin leads to increased bleeding. Similarly, TXA does not affect the function of fibrinogen.

REFERENCES

1. Gropper MA, Cohen NH, Eriksson LI, Fleisher LA, Leslie K, Wiener-Kronish JP, eds. Miller’s Anesthesia. 9th ed. Elsevier; 2020:2087.
2. Wong J, George RB, Hanley CM, Saliba C, Yee DA, Jerath A. Tranexamic acid: current use in obstetrics, major orthopedic, and trauma surgery. Can J Anaesth. 2021;68(6):894-917. doi:10.1007/s12630-021-01967-7

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