Why is plasmin not used directly as treatment?

Plasmin, an enzyme that breaks down fibrin in blood clots, is not used directly in treatment primarily because it has natural antagonists and is difficult to extract. This means that while plasmin plays a crucial role in fibrinolysis (the breakdown of blood clots), delivering it directly to the bloodstream poses significant challenges. The body has regulatory mechanisms in place, including inhibitors that can counteract plasmin's activity, which complicates the consistent and safe application of plasmin as a therapeutic agent. Additionally, the extraction and purification of plasmin from biological sources can be complex and unfeasible for clinical use.

Moreover, while other options suggest cost, effectiveness, and side effects, these factors are outweighed by the fundamental biological challenges associated with dosing and managing plasmin in live systems. Such complexities hinder its potential as a straightforward treatment modality for thrombotic conditions. In therapeutic practice, alternative fibrinolytic agents are often used instead, which can be formulated to maximize efficacy while minimizing risks.