Potential adverse reactions to warfarin sodium may include:

Fatal or nonfatal hemorrhage from any tissue or organ: This is a consequence of the anticoagulant effect. The signs, symptoms, and severity will vary according to the location and degree or extent of the bleeding. Hemorrhagic complications may present as paralysis; paresthesia; headache, chest, abdomen, joint, muscule, or other pain; dizziness, shortness of breath, difficult breathing or swallowing; unexplained swelling; weakness; hypotension; or unexplained shock.

Therefore, the possibility of hemorrhage should be considered in evaluating the condition of any anticoagulated patient with complaints which do not indicate an obvious diagnosis. Bleeding during anticoagulant therapy does not always correlate with PT/INR .

Bleeding: which occurs when the PT/INR is within the therapeutic range warrants diagnostic investigation since it may unmask a previously unsuspected lesion, e.g., tumor, ulcer, etc.

Necrosis of skin and other tissues.

Adverse reactions reported infrequently include: Hypersensitivity reactions, systemic cholesterol microembolization, purple toes syndrome, vasculitis, hepatitis, cholestatic hepatic injury, jaundice, elevated liver enzymes, fever, dermatitis, including bullous eroptions, urticaria, abdominal
pain including cramping, asthenia, nausea, vomiting, diarrhea, headache, pruritis, alopecia, and paresthesia.

Rare events of tracheal or tracheobronchial calcification have been reported in association with long-term warfarin sodium therapy. The clinical significance of this event is unknown.

Priapism has been associated with anticoagulant administration, however, a causal relationship has not been established.

Overdosage:

Signs and Symptoms: Suspected or overt abnormal bleeding (e.g., appearance of blood in stools or urine, hematuria, excessive menstrual bleeding, melena, petechiae, excessive bruising or persistent oozing from superficial injuries) are early manifestations of anticoagulation beyond a safe and
satisfactory level.

Treatment: Excessive anticoagulation, with or without bleeding, may be controlled by discontinuing warfarin sodium therapy and if necessary, by administration of oral or parenteral vitamin K1. (Please see recommendations accompanying vitamin K1preparations prior to use.)

Such use of vitamin K1 reduces response to subsequent warfarin sodium therapy. Patients may return to a pretreatment thrombotic status following the rapid reversal of a prolonged PT/INR .
Resumption of warfarin sodium administration reverses the effect of vitamin K, and a therapeutic PT/INR can again be obtained by careful dosage adjustment. If rapid anticoagulation is indicated, heparin may be preferable for initial therapy.

If minor bleeding progresses to major bleeding, give 5 to 25 mg (rarely up to 50 mg) parenteral vitamin K1. In emergency situations of severe hemorrhage, clotting factors can be returned to normal by administering 200 to 500 ml of fresh whole blood or fresh frozen plasma, or by giving
commercial Factor IX complex.

A risk of hepatitis and other viral diseases is associated with the use of these blood products; Factor IX complex is also associated with an increased risk of thrombosis. Therefore, these preparations should be used only in exceptional or life-threatening bleeding episodes secondary to warfarin
sodium overdosage.

Purified Factor IX preparations should not be used because they cannot increase the levels of prothrombin, Factor VII and Factor X which are also depressed along with the levels of Factor IX as a result of warfarin sodium treatment. Packed red blood cells may also be given if significant
blood loss has occurred. Infusions of blood or plasma should be monitored carefully to avoid precipitating pulmonary edema in elderly patients or patients with heart disease.