World Library  
Flag as Inappropriate
Email this Article

Antithyroid agent

Article Id: WHEBN0009773940
Reproduction Date:

Title: Antithyroid agent  
Author: World Heritage Encyclopedia
Language: English
Subject: Pharmacology, Antithyroid drugs, Wolff–Chaikoff effect, Corticotropin-releasing hormone antagonist, Prostaglandin antagonist
Collection: Antithyroid Drugs
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Antithyroid agent

An antithyroid agent is a hormone antagonist acting upon thyroid hormones.

The main antithyroid drugs are carbimazole (in the UK), methimazole (in the US), and propylthiouracil/PTU. A less common antithyroid agent is potassium perchlorate.

Contents

  • Graves' disease 1
  • Adverse effects 2
  • Mechanism of action 3
  • See also 4
  • References 5
  • External links 6

Graves' disease

In Graves' disease, treatment with antithyroid medications must be given for six months to two years, in order to be effective. Even then, upon cessation of the drugs, the hyperthyroid state may recur. Side effects of the antithyroid medications include a potentially fatal reduction in the level of white blood cells.

A randomized control trial testing single dose treatment for Graves' found methimazole achieved euthyroid state more effectively after 12 weeks than did propylthyouracil (77.1% on methimazole 15 mg vs 19.4% in the propylthiouracil 150 mg groups).[1] But generally both drugs are considered equivalent.

A study has shown no difference in outcome for adding thyroxine to antithyroid medication and continuing thyroxine versus placebo after antithyroid medication withdrawal. However, two markers were found that can help predict the risk of recurrence. These two markers are an elevated level of thyroid stimulating hormone receptor antibodies (TSHR-Ab) and smoking. A positive TSHR-Ab at the end of antithyroid drug treatment increases the risk of recurrence to 90% (sensitivity 39%, specificity 98%), a negative TSHR-Ab at the end of antithyroid drug treatment is associated with a 78% chance of remaining in remission. Smoking was shown to have an impact independent to a positive TSHR-Ab.[2]

Competitive antagonists of thyroid stimulating hormone receptors are currently being investigated as a possible treatment for Grave's disease.

Adverse effects

The most dangerous side-effect is agranulocytosis (1/250, more in PTU); this is an idiosyncratic reaction which generally resolves on cessation of drug. It occurs in about 0.2 to 0.3% of cases treated with antithyroid drugs.[3] Others include granulocytopenia (dose dependent, which improves on cessation of the drug) and aplastic anemia, and for propylthiouracil severe, fulminant liver failure.[4] Patients on these medications should see a doctor if they develop sore throat or fever.

The most common side effects are rash and peripheral neuritis. These drugs also cross the placenta and are secreted in breast milk. Lugol's iodine is used to block hormone synthesis before surgery.

Mechanism of action

The mechanisms of action are not completely understood. Some scientists believe that anti-thyroids inhibit iodination of tyrosyl residues in thyroglobulin. It is thought that they inhibit the thyroperoxidase catalyzed oxidation reactions by acting as substrates for the postulated peroxidase-iodine complex, thus competitively inhibiting the interaction with the amino acid tyrosine. Propylthiouracil additionally may reduce the de-iodination of T4 into T3 in peripheral tissues.[5]

See also

References

  1. ^ Homsanit M, Sriussadaporn S, Vannasaeng S, Peerapatdit T, Nitiyanant W, Vichayanrat A (2001). "Efficacy of single daily dosage of methimazole vs. propylthiouracil in the induction of euthyroidism". Clin. Endocrinol. (Oxf) 54 (3): 385–90.  
  2. ^ Glinoer D, de Nayer P, Bex M (2001). "Effects of l-thyroxine administration, TSH-receptor antibodies and smoking on the risk of recurrence in Graves' hyperthyroidism treated with antithyroid drugs: a double-blind prospective randomized study". Eur. J. Endocrinol. 144 (5): 475–83.  
  3. ^ Zambrana, J.; Zambrana, F.; Neto, F.; Gonçalves, A.; Zambrana, F.; Ushirohira, J. (2005). "Agranulocytosis with tonsillitis associated with methimazole therapy". Brazilian journal of otorhinolaryngology 71 (3): 374–377.   [1]
  4. ^ Bahn RS, Burch HS, Cooper DS, Garber JR, Greenlee CM, Klein IL, Laurberg P, McDougall IR, et al. (July 2009). "The Role of Propylthiouracil in the Management of Graves' Disease in Adults: report of a meeting jointly sponsored by the American Thyroid Association and the Food and Drug Administration.". Thyroid : official journal of the American Thyroid Association 19 (7): 673–4.  
  5. ^ Manna D, Roy G, Mugesh G (2013). "Antithyroid Drugs and their Analogues: Synthesis, Structure and Mechanism of Action". Acc. Chem. Res. 11: 2706–15.  

External links

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.