Tranexamic acid (TXA) is a medication used to manage bleeding in various medical scenarios. It functions as an antifibrinolytic agent, preventing the breakdown of blood clots. This stabilizes the body’s natural clotting process, aiding hemostasis.
How Tranexamic Acid Works
Tranexamic acid works by influencing the body’s fibrinolytic system, responsible for dissolving blood clots. TXA is a synthetic derivative of lysine that competitively binds to lysine receptor sites on plasminogen. Plasminogen, when activated, turns into plasmin, an enzyme that breaks down fibrin, the main component of blood clots.
By occupying these binding sites, TXA prevents plasminogen from interacting with fibrin, inhibiting its conversion to plasmin. This blockade preserves the integrity of the fibrin matrix, stabilizing the blood clot and preventing its premature dissolution. This mechanism ensures that clots remain intact longer, allowing for effective bleeding control.
Effective Concentrations for Topical Applications
For topical applications, tranexamic acid is used to address localized bleeding or dermatological conditions, applied directly to the skin or mucous membranes. In dermatology, TXA is recognized for its use in treating hyperpigmentation disorders, such as melasma and post-inflammatory hyperpigmentation. A 2% to 5% topical concentration has shown effectiveness in reducing melasma. Studies indicate that a 3% topical solution applied twice daily can be as effective as other standard treatments for melasma.
Topical TXA works in the skin by suppressing mediators that stimulate melanin production, reducing excessive pigmentation. This action is distinct from its role in blood clotting. Formulations like creams, gels, or liposomal serums containing these concentrations are used, and a 2% concentration can provide significant depigmentation without severe irritation. In dentistry, a 4.8% TXA solution is sometimes used as an oral rinse to control local bleeding, particularly after tooth extractions in patients on anticoagulant medications.
Effective Dosages for Systemic Uses
When tranexamic acid is administered systemically (orally or intravenously), its effectiveness is determined by the dosage in milligrams, as it circulates throughout the body. For heavy menstrual bleeding (menorrhagia), an oral dosage of 3.9 to 4 grams per day, taken for 4 to 5 days starting from the first day of the menstrual cycle, reduces blood loss by 26% to 60%.
In trauma cases with significant bleeding, intravenous administration of TXA is recommended as early as possible, ideally within three hours of injury. A typical dosage involves an initial 1 gram bolus infused over 10 minutes, followed by an intravenous infusion of 1 gram over 8 hours. This early administration has been shown to reduce the risk of death due to bleeding in trauma patients. For surgical procedures like cardiac surgery, higher total doses of tranexamic acid, exceeding 80 mg/kg, have demonstrated greater effectiveness in reducing blood loss and improving outcomes compared to lower doses.
Factors Influencing Effectiveness and Safety
Several individual factors can influence tranexamic acid’s effectiveness and safety beyond the specific concentration or dosage. A patient’s kidney function is an important consideration, as TXA is primarily excreted unchanged in the urine. Impaired kidney function can lead to increased drug levels, necessitating a dose reduction to prevent adverse effects.
A history of blood clots or active clotting disorders are contraindications for TXA use, as it stabilizes clots and could increase the risk of new clot formation. Concurrent use of other medications, such as hormonal contraceptives, may also increase the risk of thrombosis. While generally well-tolerated, common side effects include gastrointestinal upset (nausea, vomiting, or diarrhea) and headaches. More serious, though less common, side effects include seizures (particularly with high doses) and changes in vision, including color vision.