Thyroid and Antithyroid Agents

Question 1

Thyroxine (T4)

Answer 1

• Thyroid hormone – oral, IM, or IV
• ½ life 7 days, oral absorption 75-90%, converted to T3 in peripheral tissue
• Thyrotoxicosis, stress on CV system, caution in CV disease and pregnancy
• Hypothyroidism – lifelong treatment, less expensive

Question 2

Triiodothyronine (T3)

Answer 2

• Thyroid hormone – oral, IM, or IV
• 4x more potent, ½ life 1 day, oral absorption 95%
• Thyrotoxicosis, stress on CV system, caution in CV disease and pregnancy
• Hypothyroidism – lifelong treatment, more expensive

Question 3

Propylthiouracil

Methimazole

Answer 3

• Thioamide/ thioureylene – oral – initial time course is slow (thyroid stores take time to be depleted), start with high doses then switch to lower, treat 12-18 months
• Inhibit thyroid peroxidase (decrease oxidation of iodide, iodination of thyroglobulin, and coupling to form T3/T4), PTU also inhibits peripheral conversion of T4 to T3
• Skin rashes, delayed hypothyroidism, agranulocytosis, PTU in 1st trimester of pregnancy but then can switch to MMI
• Hyperthyroidism – PTU works faster but less potent and shorter action

Question 4

Potassium iodide

Answer 4

• Iodide – oral – fast effect but transient
• Inhibits release of T3 and T4, inhibits synthesis of T3 and T4
• Relatively safe – rashes, swollen salivary glands
• Hyperthyroidism (rarely alone), prevent uptake of 131I after nuclear accident

Question 5

Radioactive iodide

Answer 5

• Iodide – oral - slow
• Concentrates in thyroid and causes localized radiation damage
• Delayed hypothyroidism, radiation exposure, NOT for pregnancy or lactating moms
• Hyperthyroidism

Question 6

Propanolol

Answer 6

• B-adrenergic antagonist

* Alleviate symptoms associated with increased CV activity