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Northyx (methimazole) Disease Interactions

There are 3 disease interactions with Northyx (methimazole):


Thioamide Derivatives (Includes Northyx) ↔ Blood Dyscrasias

Severe Potential Hazard, Moderate plausibility

Applies to: Neutropenia, Thrombocytopenia

The use of thioamide antithyroid agents may infrequently be associated with the development of blood dyscrasias, primarily agranulocytosis but also leukopenia, thrombocytopenia, and aplastic anemia. Most cases of agranulocytosis occur within the first two months of therapy, with incidence declining gradually thereafter. Patients older than 40 years of age and those receiving more than 40 mg/day of methimazole appear to be at substantially increased risk (a dosage association has not been reported for propylthiouracil). Therapy with thioamide derivatives should be administered cautiously in patients with or predisposed to blood dyscrasias and/or bone marrow depression. Clinical monitoring of hematopoietic function is recommended, with particular focus on leukocyte and differential counts. Because leukopenia (i.e. leukocyte count < 4000/mm3) may also occur in 10% of patients with untreated hyperthyroidism and is often associated with relative granulocytopenia, baseline count should be determined prior to initiating antithyroid medication. Patients should be instructed to immediately report during therapy any signs or symptoms suggestive of myelosuppression such as fever, sore throat, local infection, easy bruising, or bleeding. Cessation of antithyroid drug and institution of appropriate supportive measures are necessary if agranulocytosis or aplastic anemia develops.


  1. Cooper DS "Antithyroid drugs." N Engl J Med 311 (1984): 1353-62
  2. "Product Information. Propylthiouracil (propylthiouracil)." Lederle Laboratories, Wayne, NJ.
  3. Valenta LJ, Elias AN, Weber DJ "Hyperthyroidism and propylthiouracil-induced agranulocytosis during chronic lithium carbonate therapy." Am J Psychiatry 138 (1981): 1605-7
View all 10 references

Thioamide Derivatives (Includes Northyx) ↔ Hepatotoxicity

Severe Potential Hazard, Low plausibility

Applies to: Liver Disease, Alcoholism

The use of thioamide antithyroid agents has been associated with hepatotoxic effects, including transient elevations of serum transaminases and, rarely, cholestatic jaundice, fulminant hepatitis, hepatic necrosis, encephalopathy and death. Therapy with thioamide derivatives should be administered cautiously in patients with preexisting liver disease, a history of alcohol abuse, or hepatitis. Treatment should be discontinued if deterioration in liver function or other signs of hepatic injury occur. The jaundice associated with methimazole-induced hepatitis may persist for several weeks after withdrawal of the medication.


  1. American Medical Association, Division of Drugs and Toxicology "Drug evaluations annual 1994." Chicago, IL: American Medical Association; (1994):
  2. "Product Information. Propylthiouracil (propylthiouracil)." Lederle Laboratories, Wayne, NJ.
  3. "Product Information. Tapazole (methimazole)." Jones Medical-Western Research, St. Louis, MO.
View all 13 references

Thioamide Derivatives (Includes Northyx) ↔ Hypoprothombinemia

Severe Potential Hazard, Low plausibility

Applies to: Bleeding, Coagulation Defect, Thrombocytopathy, Vitamin K Deficiency

Thioamide antithyroid agents may interfere with the action of vitamin K and have been reported in isolated cases to induce hypoprothombinemia and bleeding. Myelosuppression rarely resulting in thrombocytopenia has also been reported. Therapy with thioamide derivatives should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. Clinical monitoring of prothrombin time or INR is recommended.


  1. "Product Information. Propylthiouracil (propylthiouracil)." Lederle Laboratories, Wayne, NJ.
  2. Sammon TJ, Peden VH, Witzleben C, King JP "Disseminated intravascular coagulation complicating propylthiouracil therapy. A case description of a 16-year-old girl." Clin Pediatr (Phila) 10 (1971): 739-42
  3. "Product Information. Tapazole (methimazole)." Jones Medical-Western Research, St. Louis, MO.

Northyx (methimazole) drug Interactions

There are 66 drug interactions with Northyx (methimazole)

Drug Interaction Classification

The classifications below are a general guideline only. It is difficult to determine the relevance of a particular drug interaction to any individual given the large number of variables.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No information available.

Do not stop taking any medications without consulting your healthcare provider.

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