General principles and indications for use
Antifibrinolytic agents (or fibrinolysis inhibitors) are a crucial tool in the physician's arsenal for combating bleeding. The main goal of their use is to stop blood loss caused by excessive, pathological activity of the fibrinolytic system.
When the system that destroys blood clots works too actively, the patient risks losing a critical volume of blood. In such cases, drugs of this group are prescribed.
Main clinical indications include:
- Surgery and traumatology: extensive trauma, major surgical interventions, and childbirth.
- Liver pathologies: diseases that disrupt the natural synthesis of blood coagulation factors or endogenous fibrinolysis inhibitors.
- Local bleeding: menorrhagia (heavy menstrual bleeding) and prostatitis.
- Iatrogenic conditions: overdose of fibrinolytic drugs (when artificially induced fibrinolysis needs to be stopped urgently).
Mechanisms of action
Globally, all drugs in this group are divided into two categories based on their basic principle of action:
- Agents that inhibit plasminogen activation (preventing the precursor from becoming an active enzyme).
- Agents that directly inhibit plasmin (blocking the already formed enzyme).
Aminocaproic and tranexamic acid preparations
These are synthetic analogues widely used in clinical practice. They are administered both orally (per os) and intravenously.
Aminocaproic acid (Aminocaproic acid) features an interesting dual mechanism of action:
- First, it binds to plasminogen, reliably blocking its conversion into active plasmin.
- Second, if plasmin has already formed, the drug prevents its destructive effect on fibrin threads.
However, the drug has a number of side effects. Cardiovascular effects may include arterial hypotension, bradycardia, and arrhythmias. Patients also complain of dizziness and dyspepsia (nausea, diarrhea).
Its structural analogue — aminomethylbenzoic acid (known under the trade names Amben or Pamba) — has an absolutely similar mechanism of action.
Tranexamic acid (Tranexamic acid, trade names: Tranexams, Cyclokapron) works by inhibiting plasminogen activation. Compared to aminocaproic acid, tranexamic acid significantly outperforms its predecessor in clinical efficacy and has a more prolonged duration of action.
Side effects of tranexamic acid include:
- Dyspeptic disorders: anorexia, nausea, vomiting, and diarrhea.
- Neurological disorders: dizziness and pronounced drowsiness.
- Allergic reactions: predominantly skin manifestations.
Aprotinin — a proteolytic enzyme inhibitor
Aprotinin (trade names: Gordox, Contrical, Trasylol, Ingitril) is a potent inhibitor of proteolytic enzymes.
Its key mechanism of action is the direct inhibition of plasmin, which is the main enzyme of the fibrinolysis process. In addition, aprotinin is able to suppress the activity of other proteolytic enzymes in the body.
Unlike synthetic acids, aprotinin is administered exclusively via the intravenous route.
When using it, the physician must be prepared for the following side effects:
- Cardiovascular system: development of tachycardia and arterial hypotension.
- Gastrointestinal tract: bouts of nausea and vomiting.
- Immune system: high risk of allergic reactions.
Briefly: answers to topical questions
What are the absolute contraindications to the use of tranexamic acid?
- Renal bleeding is a contraindication to the use of tranexamic acid.
- High risk of thrombotic complications is a contraindication to the use of tranexamic acid.
It is easy to remember the mechanism of aminocaproic acid using the "double block" rule: it prevents plasminogen from "waking up" (becoming plasmin), and if it has already "woken up," it ties its hands, preventing it from destroying fibrin.
Class and exam questions
What is the main difference between tranexamic acid and aminocaproic acid?
Tranexamic acid outperforms aminocaproic acid in clinical efficacy and has a more prolonged duration of action, although both block plasminogen activation.
How exactly does aprotinin work?
Aprotinin is a proteolytic enzyme inhibitor. It acts directly — inhibiting plasmin itself (the main enzyme of fibrinolysis), and also suppressing other proteases.
Why are these drugs prescribed for liver diseases?
In severe liver pathologies, the synthesis of own blood coagulation factors and natural fibrinolysis inhibitors is impaired, leading to a high risk of uncontrolled bleeding.
What else to study on this topic
- Comparative characteristics of oral and intravenous routes of administration of synthetic analogues.
- Mechanisms of development of cardiovascular complications (arrhythmias, bradycardia) when taking aminocaproic acid.
- Specifics of using antifibrinolytics in case of overdose with fibrinolytic drugs.
- Effect of aprotinin on other proteolytic enzymes besides plasmin.
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