Ancrod (current brand name: Viprinex) is a defibrinogenating agent derived from the venom of the Malayan pit viper. Defibrinogenating blood produces an anticoagulant effect. Ancrod is not approved or marketed in any country. It is a thrombin-like serine protease. Medical use As of 2017 ancrod was not marketed for any medical use. Pregnancy Category X : Ancrod was not found to be teratogenic in animal studies, but some fetal deaths occurred as a result of placental hemorrhages in animals given high doses; therefore, it should not be used during pregnancy as the defibrinogenation mechanism of ancrod might be expected to interfere with the normal implantation of the fertilized egg. Contraindications and precautions Known bleeding disorders of any origin or any unexplained excessive bleedings in the past. Platelet counts of less than 100,000 (even if asymptomatic), exemption : HIT (Heparin- induced thrombocytopenia). Planned surgery or short before delivery. Active ulcerations of the GIT. Any kind of malignant disease. Renal stones (increased likelihood of significant urological bleeding). Severe and uncontrolled arterial hypertension. Active pulmonary tuberculosis. Impaired fibrinolysis. Severe liver disease. Manifest or impending shock. I.M.-Injection : Ancrod should not be injected i.m., because of rapid induction of neutralizing antibodies and thus drug resistance. Side effects In clinical trials for ischemic stroke, ancrod increased the risk of intracerebral hemorrhage. Hypersensitivity reactions : Local or generalized skin reactions (rash and urticaria); appearance of neutralizing antibodies to ancrod with partial or total loss of ancrod activity (drug resistance). Sometimes pain at injection site (normally mild). This side effect may be, if necessary, treated with local or oral antihistaminic drugs (e.g., clemastine, or diphenhydramine). Bleeding at injection site, thrombophlebitis at local veins, and (paradoxical) arterial thrombotic events. Occasionally deposition of cleaved fibrinogen derivates in the spleen resulting in splenomegaly; rupture is possible, if the spleen is palpated too strongly (life-threatening bleeding and need of splenectomy may result). Specific side effects are local and systemic bleeding events. Local bleeding events may be treated with local pressure or surgical dressings, if necessary. Compared with other anticoagulants the risk of systemic bleeding is relatively low. If systemic bleeding is severe enough to warrant fast reversal of ancrod action, fibrinogen should be substituted (please refer to section 'special antidotes'). Occasionally, increased headache has been found in patients with known migraine. Also, chills and fever may occur infrequently. Thrombocytopenia as side effect has never been noticed with ancrod in contrast to