Amiodarone induced hypothyroidism

• incidence
  • in areas with high iodine intake - 13%
  • in areas of low iodine intake - 6.4%
  • patients with low environmental iodine e.g. Italy develop more amiodarone induced hyperthyroidism than amiodarone induced hypothyroidism - the opposite occurs where there is high environmental iodine e.g. UK, USA
    
• diagnosis
  • low T3, T4; increased TSH
  • in the first three months of amiodarone therapy there may be a transient increase in TSH levels
    
    
• treatment
  • continue amiodarone therapy in combination with thyroxine therapy

Notes (1,2,3):

• about 37% of amiodarone contains organic iodine by molecular weight
  • each 200 mg tablet is estimated to contain about 75 mg of organic iodide of which 10% (7.5 mg) is de-iodinated to yield free iodine
    • results in a high iodine supply to the body that far exceeds the daily recommended optimal iodine intake (0.2 to 0.8 mg)
• elimination half-life of amiodarone is about 2-3 months, and total body iodine stores may remain elevated for up to 9 months even after discontinuation of the drug
• amiodarone-induced thyroid dysfunction is a complex phenomenon; however, its exact pathogenesis largely remains unknown

Reference:

• BMJ 1999;319:894-99.
• Harjai KJ, Licata AA. Effects of amiodarone on thyroid function. Ann Intern Med. 1997;126:63-73
• Bogazzi F, Tomisti L, Bartalena L, Aghini-Lombardi F, Martino E. Amiodarone and the thyroid a 2012 update. J Endo-crinol Invest. 2012;35:340-8