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Vitamin K₁ is a specific antidote for anticoagulants, such as anisindione, which reduce prothrombin activity in the blood. Vitamin K₁ may be administered orally or by injection, if the patient is not bleeding or if bleeding is slight. A few hours after administration of vitamin ^K1 preparations, such as phytonadione, prothrombin activity increases and clotting time decreases. In the presence of more active hemorrhage, however, transfusions of whole blood or plasma are required until the desired level of prothrombin activity is achieved. Treatment with vitamin ^K1 preparations is only adjunctive in such cases.

All contraindications to oral anticoagulant therapy are relative rather than absolute. Contraindications should be evaluated for each patient, giving consideration to the need for and the benefits to be achieved by anticoagulant therapy, the potential dangers of hemorrhage, the expected duration of therapy, and the quality of patient monitoring and compliance.

In general, oral anticoagulants are contraindicated in patients who are bleeding or who have hemorrhagic blood dyscrasias or hemorrhagic tendencies (eg, hemophilia, polycythemia vera, purpura, leukemia) or a history of bleeding dia-thesis. They are contraindicated in patients with recent cerebral hemorrhage, active ulceration of the gastrointestinal tract, including ulcerative colitis, or open ulcerative, traumatic, or surgical wounds. Oral anticoagulants may be contraindicated in patients with recent or contemplated brain, eye, or spinal cord surgery or prostatec-tomy, and in those undergoing regional or lumbar block anesthesia or continuous tube drainage of the small intestine. Oral anticoagulants may be contraindicated in patients who have severe renal or hepatic disease, subacute bacterial endocar-ditis, pericarditis, polyarthritis, diverticulitis, visceral carcinoma, or aneurysm. Other conditions in which the oral anticoagulants may be contraindicated include severe or malignant hypertension, eclampsia or preeclampsia, threatened abortion, emaciation, malnutrition, and vitamin C or K deficiencies. Since a high degree of patient cooperation is required for the outpatient use of oral anticoagulants, a lack of such cooperation is a relative contraindication to their use.

Pregnancy: Anisindione is contraindicated in pregnancy because the drug crosses the placental barrier. Oral anticoagulants may cause fetal damage when administered to pregnant women. Fetal or neonatal hemorrhage and intrauterine fetal death have occurred even when maternal prothrombin times were within the therapeutically accepted range. Maternal use of warfarin and anisindione during the first trimester of pregnancy has been reported to cause hypoplastic nasal structures or other signs of the Conradi-Hunermann syndrome in the offspring. These patients received other drugs in addition to anticoagulants and a positive causal relationship has not been established. If oral anticoagulants must be used during pregnancy, or if the patient becomes pregnant while taking one of these drugs, the patient should be apprised of the potential hazard to the fetus. The possibility of termination of the pregnancy should be considered in light of these risks.

As an alternative to the use of oral anticoagulants in pregnant patients, the use of heparin, which does not cross the placenta, should be considered.

Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.