Hirudin is the anticoagulant component of the saliva of medicinal leech and inhibits thrombin by formation of irreversible complexes through binding of its active site.

What is the difference between hirudin and heparin?

Hirudin is a direct thrombin inhibitor that interacts with both clot-bound and circulating thrombin. This action is different from the indirect thrombin inhibition of unfractionated or low-molecular-weight (LMW) heparin.

How long does hirudin last?

The effects of the hirudin may last up to a few hours. You can tell that it's no longer active when the blood stops draining. It is at that time that you should apply another leech, unless directed by the physicians to do otherwise. In most instances, you need only apply one or two leeches at a time.