Drugs For Treating Hyperthyroidism

Hyperthyroidism results from excess production of thyroid hormones due to various reasons. Treatment of the resulting thyrotoxicosis (Basedow's disease) consists of using drugs that inhibit excess synthesis of hormones, as well as using radioactive iodide in order to disrupt or remove thyroid gland follicles with excess activity.

Drugs used for hyperthyroidism can be classified as drugs that suppress thyroid hormone synthesis in the anterior lobe of the hypophysis, and they consist of diiodotyrosine and iodine, as well as drugs that suppress thyroid hormone synthesis in thyroid glands (propylthiouracil, methylthiouracil, methimazole, and carbimazole).

The most useful drugs used for this purpose are classified as thioamides. They are chemically similar and contain thiourea-like thioamide functional groups. The most preferred are propylthiouracil and methimazole, although methylthiouracil and carbimazole are widely used.

Thioamides are reducing agents. They inhibit thyroid hormone synthesis by inhibiting the peroxidase enzymatic system, which catalyzes oxidation of iodide ions and iodine that are consumed in food, which is necessary for iodination of tyrosine derivatives. Thus they reduce the concentration of free iodine necessary to react with tyrosine derivatives, and they can also block oxidative addition reactions of mono- and diiodtyrosines, which form L-thyroxine and L-triiodothyronin.

Drugs that inhibit absorption of iodine by the thyroid gland are sometimes used to treat thyrotoxicosis, in particular potassium chlorate.

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaI131). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak ¡-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion.

Diiodotyrosine: Diiodotyrosine, 3,5-diiodotyrosine (25.2.1), is synthesized by directly iodi-nating tyrosine with iodine in the presence of sodium iodide in aqueous ethylamine, or in a mixture of acetic and hydrochloric acids with the addition of hydrogen peroxide [10-12].

Diiodotyrosine does not possess pronounced hormonal activity. However, it stops production of thyrotropic hormone by the anterior lobe of the hypophysis, which activates thyroid gland activity.

It is used for hyperthyroid forms of endemic and sporadic goiters, diffuse, toxic goiters, and other illnesses accompanied by thyrotoxicity. Synonyms of this drug are ditirin, iodoglobin, and others.

Propylthiouracil: Propylthiouracil, 6-propyl-2-thio-2,4-(1H,3H)-pyrimidindione (25.2.2), is synthesized by condensating ethyl butyroacetate with thiourea in the presence of sodium ethoxide [13].

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