How are drugs used to control Thyrotoxicosis?

The majority of patients placed on anti-thyroid drugs will have normal thyroid function tests within four weeks, side effects are rare. After 12 months of treatment 50% of patients are cured and need no further treatment. The remainder will need radioactive iodine or surgery. Drug treatment may be given in two ways:

1. Block and replace method: Large doses of antithyroid drugs are given with thyroid hormone. (This method must not be used in pregnancy). The advantage of this method is that it is an easy regime (4O mgs of carbimazole with 100 micrograms of thyroxine all taken first thing in the morning.) In the UK carbimazole is the drug of choice. Elsewhere propylthiouracil is commonly used.

2. Titration method: In this method a large dose of carbimazole (40 mgs) is started and every 4 weeks as long as the thyroid levels are satisfactory the dose is reduced by 5-10 mgs. Maintenance doses of 5-20mgs are usual.

Iodine itself has a remarkable ability to control thyrotoxicosis. Its effect is short lived but it is useful in patients who are allergic to antithyroid drugs and cannot take beta-blockers (see below). Fourteen days treatment with Lugol's iodine (0.5mls three times a day) will allow the most severe thyrotoxic patient to undergo safe surgery .The effect is short lived and there is a small window of opportunity for surgery.

Beta-blockers are very useful in the management of thyrotoxicosis. They are completely contraindicated in patients with a history of asthma. Propanolol will control cardiac symptoms but should not used in heart failure. The drug is useful when combined with antithyroid drugs or radioactive iodine and may be stopped when these treatments have come into effect. Beta-blockade alone may be used to prepare even the most toxic patient for surgery. When combined with Lugol's iodine surgery can take place after seven days. The beta-blocker should be continued over the intraoperative period and for the subsequent seven days. Failure to administer the beta-blockers during the intra operative period may result in a thyroid storm.

Do Antithyroid drugs have any side effects?

Side effects are rare and usually trivial but include:

  • Bone marrow damage: This is rare and presents as sore throat, fever and mouth ulcers. The patient must report to hospital immediately and stop the tablets. Recovery of the bone marrow occurs in 2 weeks
  • Rashes, pruritus, or joint swelling are common. If the symptoms are mild then the drug may be continued, but in severe cases the carbimazole should be changed to propylthiouracil or vice versa.