Mode of Action
The leech’s main therapeutic benefits are not derived from the average 5 mls of blood removed during biting (although this may provide dramatic relief at first), but from the anticoagulant and vasodilator contained in the leech saliva. These properties permit the wound to ooze up to 50 mls of blood for up to 48 hours. Leech bites will bleed (ooze) up to 150 ml of blood for an average of 10 or more hours. The goal then is to produce an adequate venous outflow from the tissue by adjusting the number of bite wounds to suit the clinical applications; for example, 6 leech bites could produce up to 300 mls total venous ooze. Leech therapy is usually required for 3-7 days, until new vessel ingrowth around flap margins develops sufficiently to restore effective venous drainage.
However, since some cases have been known to take 10 days or more, it is important that treatment be continued for a sufficient period of time to avoid failure. Leech therapy should be continuous as long as signs of venous insufficiency persist between leech applications. When the skin stays pink after leech venous oozing ceases, leech therapy can be stopped.
The ability of the leech bite wound to continue bleeding locally for 24-48 hours appears to be related to pharmacologically active secretions(not the anticoagulant alone) introduced by the leech bite. Efforts to simulate this effect by introducing conventional anticoagulants, such as heparin, into small stab wounds in the skin have been unsuccessful.