**8.4. Lithium**

172 Thyroid Hormone

mild hypothyroidism.

normal, and low iodine diet.

Antithyroid drugs can be used as a primary treatment or as a preparatory treatment before radioiodine or surgery. The antithyroid drugs are usually started in higher doses. The starting dose of methiomazole or carbimazole is 10-20 mg every 8-12 hours and that of propylthiouracil is 100-200 mg every 6-8 hours. Once euthyroidism is achieved which usually takes 4-5 weeks, methimazole can be given in single daily dose while propylthiouracil is given in multiple daily doses throughout the treatment. There are two treatment strategies for using antithyroid drugs. In titration regimen, antithyroid drugs are started in high doses and dose can be gradually decreased to maintain euthyroid state. In Block and Replace regimen, the antithyroid drugs are maintained in high doses and subsequently levothyroxine is added to maintain the euthyroid status. At present there is no

Patient should be reviewed clinically and biochemically after every 3-4 weeks. Dose of antithyroid drugs is adjusted based on the TT4 or FT4 level, as TSH level often remain suppressed for several months. The usual daily maintenance dose of carbimazole or methimazole is 2.5 – 10 mg and that of propylthiouracil is 50-100 mg. When TSH level become normal, it can also be used to monitor therapy. Size of the goiter decreases in about 30-50% of patients during treatment. In remaining patients it may remain unchanged or even enlarge. Increase in goiter size is one of the earliest manifestations of iatrogenic hypothyroidism. The other features are weight gain, lethargy, fatigue and other signs of

Maximum remission rate with antithyroid drugs is 30-50%, which can be achieved by continuation of the drug for 6-18 months or even longer. Most of the relapses occur within first 3-6 months after discontinuation of drug. Suppressed TSH level below the normal limit is the first signal of relapse even in the presence of a normal serum T4 level. In most of the studies, the relapse rate is 50-80%.48,49 Most important predictor of relapse is goiter size.50 Other factors influencing recurrence of Graves' disease include high TSHR-Ab concentration, large iodine intake, marked residual goiter, short duration of antithyroid drug treatment and previous recurrence. Factors which favor long term remission after therapy include the initial presence of T3 toxicosis, a small goiter, decrease in the size of goiter, and return of TSH to normal during treatment, the return of serum thyroglobulin to

Most common side effects of thionamides are pruritus, skin rash, urticaria, fever and arthralgia. These may resolve spontaneously or after substituting another drug. Rare but major side effects are hepatitis, cholestasis, SLE like syndrome, ANCA positive vasculitis and most importantly agranulocytosis. Major side effects occur in less than 1% of patients.Antithyroid

Inorganic iodine acts in many ways in thyrotoxicosis. Iodine blocks its own transport in thyroid, inhibits iodine organification and inhibits the release of hormone. Inhibition of iodine organification by inorganic iodide is known as Wolf-Chaikoff effect. Major action of

drugs should be stopped and not restarted if patient develop major side effects.

**8.2. Iodine and iodine containing components** 

proven advantage of block and replace regimen over titration regimen.

Lithium also acts as a thyroid constipating agent (block the release of thyroid hormones). Lithium also potentiates the beneficial effect of radioiodine. The usual dose of lithium is 450- 900 mg per day in divided doses. Serum lithium concentration should be maintained at 1meEq/L. No adverse effects are reported with this dose of lithium.
