Over the last twenty years, use of hirudin in clinical situations for thrombin reduction has been studied, especially when the typical thrombin reduction drug, heparin, causes an adverse reaction in patients receiving that therapy.
As the natural hirudin in leech saliva is known to be the most potent anticoagulant on the market, its value to clinical and medical science is unparalleled; however, producing large enough amounts from natural sources proved to be unconventional and extremely expensive. A pharmacological solution to this supply problem was found in recombinant hirudin, also known as r-hirudin, which has been developed to produce large amounts of hirudin-based proteins that are purified for clinical use.
The drugs using this r-hirudin are lepirudin (Refludan) , hirudin derived from Hansenula (Thrombexx, Extrauma) and desirudin as well as several other direct thrombin inhibitors chemically derived from hirudin.
Lepirudin is a recombinant hirudin derived from yeast cells and almost completely identical to natural hirudin. It is used in medical cases where heparin-induced thrombocytopenia has been caused by the use of heparin as an anticoagulant. Due to hirudin’s ability to target fibirinogen directly without affecting other serum proteins, it is able to provide the same anticoagulant function as heparin without the side effects.
Thrombexx is an r-hirudin derived from the Hansenula type yeast organism. It has been developed as an alternative anticoagulant on the market to specifically prevent deep venous thrombosis in general surgical procedures and to treat heparin-induced thrombocytopenia.
Extrauma is a topical version of the r-hirudin compound that is used to treat contusions, distortions, muscular tears, traumatic hematomas, varicosities and preiphlebitis. It has a dual effect as anti-thrombotic and anti-inflammatory.
Thrombexx and Extrauma are derived from a yeast culture named ogataea polymorpha, an organism determined to be safe by the World Health Organization because it does not contain pyrogens, pathogens or viral inclusions.
Desirudin is an r-hirudin used to prevent deep vein thrombosis (DVT) in patients undergoing elective hip and knee replacement surgery. In studies, desirudin has been shown to have been more effective in preventing DVT than heparin or enoxaparin.
These r-huridin drugs all share the same traits as opposed to heparin and enoxaparin:
They have a single mechanism of action independent of anti-thrombin III. They form equimolar complexes with thrombin, blocking the active center of the enzyme.
They bind directly to both free and clot-bound thrombin to inhibit activity.
There is no action on other components of the haemostatic system and its effect is not inhibited by activated platelets or other molecules which neutralize heparin.
Another drug, bivalirudin, is what is considered a synthetic congener hirudin; this means it is almost a direct clone of the naturally occurring drug. It varies from the other direct thrombin inhibitors in that it is reversible, whereas the others are “nearly irreversible”. This means the effects of the bivalirudin drug wear off with natural liver function cleansing it from the body’s system within 30 minutes. It has been recommended for use in patients with unstable angina undergoing percutaneous transluminal coronary angioplasty and as an anticoagulant in patients undergoing percutaneous coronary intervention. It is also recommended for the same instances that the other r-hirudin drugs are recommended specifically when patients have are at risk of getting heparin induced thrombocytopenia.
With all of these benefits, it may seem crazy not to use them instead of heparin. Unfortunately, these r-hirudin based drugs are anywhere from five to thirty times as expensive as heparin. Even with the ability to artificially synthesize hirudin, it is still not as economical as heparin. Of course, obtaining enough of it from a natural source has proven even more expensive in the past.