What Are the Different Types of Thyroid Medicine?

Antithyroid drugs (ATD) are drugs that can eliminate (temporary or long-term) symptoms of hyperthyroidism (hyperthyroidism). Clinically used antithyroid drugs are thioureas, iodine and iodide, radioactive iodine, and beta receptor blockers.

1 Antithyroid drugs 1, thioureas

Thiourea drugs are a class of small molecule substances containing thiol and thiourea groups, and they are also the most commonly used antithyroid drugs. Thiourea antithyroid drugs were introduced into the clinic in 1940, and are divided into thiouracil and imidazole. The thiouracil includes Methylthi-ouracil (MTU) and propylthiouracil (PTU). ; Imidazoles include methimazole (MMI), carbimazole (CMZ). ^[1]

1 Antithyroid drugs (1) Thioxurams

Thiopyrimidines include Propylthiouracil (PTU) and Methylthi-ouracil (MTU).

Mechanism of action: Inhibition of thyroid hormone synthesis: By inhibiting thyroid peroxidase, and then inhibiting tyrosine iodination and coupling, iodine oxide cannot be bound to thyroglobulin, thereby inhibiting thyroid hormone biosynthesis. Attenuates -receptor-mediated glucose metabolism to suppress T4 conversion in peripheral tissues and T3 immunosuppression. For patients with T3 hyperthyroidism and hyperthyroidism crisis. Because it does not work on the hormones that have been synthesized, the clinical effect will not be effective until at least 2 to 4 weeks after taking the medicine. If iodine-containing drugs or foods containing more iodine have been applied before taking antithyroid drugs, the excretion of thyroid hormones is delayed, and the onset of the drug is slow. In addition, propylthiouracil has an immunosuppressive effect, can inhibit the formation of thyroid autoantibodies, promote the disappearance of blood thyroxine receptor antibodies, and is conducive to the relief of hyperthyroidism.

Adverse reactions: The adverse reactions of propylthiouracil are common headache, dizziness, joint pain, rash, skin itching, gastrointestinal discomfort, liver function damage, granulocytopenia and so on. (1) Deficiency of granulocytes (granulocyte count less than 0.5 × 109 · L-1) can lead to infection, life-threatening, and serious adverse reactions. Its incidence rate is 0.1% to 0.3%, and the relationship with the dose is not clear. It tends to occur in older people. Leukopenia and agranulocytosis often occur from 2 to 6 weeks after administration, but can also be seen at any time after administration. There is no pre-existing symptom. Sudden onset of symptoms should be checked regularly. If there is fever and sore throat, attention should be paid to check the blood. Those with a white blood cell count of less than 3 × 109 · L-1 or a neutrophil count of less than 1.5 × 109 · L-1 must be discontinued immediately and actively treated. (2) Hepatic impairment is another important adverse reaction to antithyroid drugs. The active metabolite formed by propylthiouracil in the body has hepatotoxicity, which causes different degrees of hepatocyte necrosis, which is mainly manifested by elevated transaminase and occasionally hepatic necrosis. (3) Neutrophil cytoplasmic antibody (ANCA) -associated microangiitis is another adverse reaction of PTU. Small vasculitis is more common in kidney involvement, leading to severe proteinuria and progressive renal impairment. Other manifestations are fever, arthralgia, myalgia, cough, bloody or hemoptysis in the sputum.

2 Antithyroid drugs (2) imidazoles

Methimazole (Tabazole) and Carbimazole (Carbimazole). Carbimazole is hydrolyzed into methimazole in the body to exert its pharmacological effect, and its efficacy per 15 mg is equivalent to that of methimazole 9.2 mg.

Mechanism of action: The antithyroid effect of methimazole is similar to that of propylthiouracil. Metimazole does not block 5-deiodinase activity, and it cannot block the conversion of T4 to T3 in peripheral tissues. It is not the first antithyroid drug for thyroid crisis. Metimazole blocked the synthesis of thyroid hormone slightly stronger than propylthiouracil, and the duration of the effect was longer, it did not bind to plasma proteins.

Adverse reactions: Methimazole is less likely to cause microangiitis, and its liver damage is mainly jaundice, and bilirubin is significantly increased. After stopping the drug, it can show complete but slow recovery. Granulocyte deficiency caused by methimazole is dose-dependent. Methimazole can also cause insulin autoimmune syndrome.

2 Antithyroid drugs 2, iodine and iodide

(1) Commonly used compound iodine solution ( Lugo's solution )

Pharmacological effects:

Small doses of iodine can prevent simple goiter; large doses of iodine can inhibit the release of thyroid hormones and can also antagonize TSH to promote hormone release.

Clinical use: Preparation for hyperthyroidism before surgery. The application of large doses of iodine 2 weeks before surgery can inhibit the effect of TSH on promoting the proliferation of glands, shrink the glands and reduce their blood vessels, facilitate surgery and reduce bleeding. The treatment of thyroid crisis can inhibit the release of thyroid hormones, while taking thiourea drugs.

The main adverse reactions are:

General reactions, such as throat discomfort, metallic taste in the mouth, and respiratory tract irritation; Allergic reactions, such as fever, rash, dermatitis, and angioedema, in severe cases, throat edema; Induced thyroid dysfunction, such as hyperthyroidism, hypothyroidism And goiter.

3 Antithyroid drugs 3, radioactive iodine

In 1942, radioactive 131 iodine was used for the first time as a treatment for hyperthyroidism. It is an effective antithyroid drug. Thyroid cells have a special affinity for iodide. After oral administration of a certain amount of 131 iodine, it can be absorbed by the thyroid gland in large quantities. The 131 iodine with harmful effects can be implanted into thyroid tissue. When 131 iodine decays into 131 xenon, it can emit Beta rays (99%) and gamma rays (1%). The former has an effective range of only 0.5 to 2 mm, which can selectively destroy the thyroid acinar epithelium without affecting adjacent tissues. The thyroid tissue can be exposed to concentrated light for a long time. After the glands are destroyed, they gradually die and become non-functional. Connective tissue, thereby reducing the secretory function of the thyroid gland, so that hyperthyroidism can be cured, achieving the purpose similar to subtotal thyroidectomy. So some people call 131 iodine the treatment of hyperthyroidism as "medical thyroid surgery."

Clinical application in the treatment of hyperthyroidism, thyroid cancer, thyroid iodine uptake function test. ^[2]

4 Antithyroid drugs 4, beta-blockers

Propranolol is an adjuvant treatment for hyperthyroidism and thyroid crisis. Symptoms of sympathetic nerve activation caused by hyperthyroidism can be improved by blocking receptors; propranolol and oxenolol can also reduce T3 production. Applicable to those who are not suitable for other antithyroid treatment, and can improve the symptoms of thyroid crisis. Feces alone have limited control symptoms. If combined with thiourea drugs, the effect is rapid and significant. ^[3]