Drug treatment of hyperthyroidism

Seek specialist advice.

• beta blockers for control of adrenergic symptoms
  • e.g. - propranolol modified release 80 mg once or twice daily (contraindicated in patients with asthma)
    
    
• anticoagulation – in atrial fibrillation
  
  
• antithyroid drugs (ATDs)
  • are thionamides and they block T3 and T4 synthesis by inhibiting thyroid peroxidise (2)
    
    
  • drugs include: propylthiouracil, carbimazole, and its active metabolite methimazole
    • carbimazole or methomazole are preferred due to
      • small risk of serious liver injury (about 1 in 10 000 adults) associated with propylthiouracil use
      • once daily dose (when compared to every eight or 12 hours as is the case for propylthiouracil)
      • the longer half life (leads to more rapid control)
        
        
  • can be used for
    • long-term therapy - remission in patients with Graves' disease, especially in those presenting under the age of 40
    • short-term control of thyrotoxicosis – to normalise thyroid function in order to
      • prevent exacerbation of hyperthyroidism after I-131 ablation
      • avoid surgical risks associated with uncontrolled hyperthyroidism
        
        
  • majority of patients with Graves’ become euthyroid by 4-8 weeks treatment with methimazole (15-30 mg daily) or carbimazole (20-40 mg daily)
    • in severe hyperthyroidism (free thyroxine >70 pmol/L), large goitre, or recent exposure to iodide (including contrast media used for computed tomography), treatment may be continued for a longer time or treat with larger thionamide doses
      
      
  • once euthyroid is achieved, two regimens can be employed:
    • block-replace
    • titrated
      
      
  • rates of remission are lower in males, in older patients, and in those patients with severe hyperthyroidism
    
    
  • antithyroid drugs are ineffective in thyroiditis (viral, postpartum or amiodarone induced) - this is because the action of the antithyroid drugs is to block production of thyroid hormones whereas the hyperthyroidism associated with thyroiditis is caused by release of stored thyroid hormone from damaged thyroid cells

NICE note with respect to the use of antithyroid drugs for adults, children and young people with hyperthyroidism (3):

• before starting antithyroid drugs for adults, children and young people with hyperthyroidism, check full blood count and liver function tests
• when offering antithyroid drugs as first-line definitive treatment to adults with Graves' disease, offer carbimazole for 12 to 18 months, using either a block and replace or a titration regimen, and then review the need for further treatment
• when offering antithyroid drugs to children and young people with Graves' disease, offer carbimazole, using a titration regimen, and review the need for treatment every 2 years
• when offering life-long antithyroid drugs to adults with hyperthyroidism secondary to a single or multiple toxic nodules, consider treatment with a titration regimen of carbimazole
• consider propylthiouracil for adults:
  • who experience adverse reactions to carbimazole
  • who are pregnant or trying to become pregnant within the following 6 months
  • with a history of pancreatitis.

Stop and do not restart any antithyroid drugs if a person develops agranulocytosis. Refer to a specialist for further management options.

Reference:

• (1) Vaidya B, Pearce SH. Diagnosis and management of thyrotoxicosis. BMJ. 2014;349:g5128
• (2) Kravets I. Hyperthyroidism: Diagnosis and Treatment. Am Fam Physician. 2016;93(5):363-70.
• (3) NICE (November 2019). Thyroid disease: assessment and management