Thyroid Drugs

Question 1

Levothyroxine

Answer 1

1. DOC for treating hypothyroidism
2. MOA
   - sodium salt of T4- produces normal levels of T3 and T4
3. Indications
   - tx simple non-endemic goiter, hashimotos disease, and thyrotropin dependant thyroid carcinoma
   - prevent goiter resulting from drugs that interfere with thyroid function such as Li, aminosalicylic acid, and sulfonamides
4. Doses titrated to the individual, doses should keep TSH levels in the normal range, changes in function T4 and TSH occur slowly, TSH levels measured 4-6wks after adjusting the dose of T4

Question 2

Liothyronine Sodium

Answer 2

1. Sodium salt of T3, short half life and duration of action
2. Indications
   - used in initial therapy of myxedema and myxedema coma
   - achieves normal thryoid activity faster
   - NOT used for maintenance tx

Question 3

Liotrix

Answer 3

1. MixTure of T4 and T3

Question 4

SE of hypothyroid therapy

Answer 4

hyperthyroidism - resembles sympathetic stimulation

- cardiac palpitation, tachycardia, weight loss, insomnia, angina pectoris, tremor, heat intolerance, inc. appetite

Question 5

Methimazole and Propylthiouracil

Answer 5

1. Thioamide derivatives
2. MOA:
   - Inhibit synthesis of thyroid hormone in thyroid gland
   - dec incorporation of iodine, dec. synthesis, and prevent coupling
   - cause gradual dec. in thyrotoxicosis b/c circulating T3 and T4 will still affect receptors
   - propylthiouracil dec. peripheral conversion of T4 to T3 which may produce a slightly more rapid effect
   - Methimazole: more potent and longer acting the PTU- but no inhibition of conversion
3. Indications
   - First line Tx for graves disease
   - used in conjunction with radioactive iodine for thyrotoxic crisis
   - used to prepare pts for subtotal thyroidectomy
4. SE
   - PTU: severe liver injury, and acute liver failure, should only be used in those who cannot tolerate methimazole, DOC for early pregnancy (1st trimester only
   - serious itching and skin rash
   - granulocytopenia and agranulocytosis - sore throat
   - headaches, N/V, jaundice, myalgia, arthralgia, Lupus-like syndrome, lymphadenopathy, psychosis
   - prolonged admin: goiter formation, esp in pregnancy - keep dose low

Question 6

Iodide

Answer 6

1. oldest therapy
2. MOA
   - excess iodide will dec synthesis of T3 and T4
   - rapid dec. in the release of thyroid hormone
3. Indications
   - used prior to thryoid surgery b/c it dec. vascularity and thyroid content of the gland (prevents thyroid storm)
   - prevent uptake of radioactive iodine in the event of accident (radioactive material spill)
4. Effect wears off after 2-8wks resulting in thyroxicosis - not a good tx alone for hyperthyroidism

Question 7

Radioactive Iodine

Answer 7

1. MOA:
   - becomes trapped in the gland and beta rays destroy the tissue
2. Indications
   - used hyperthryoidism in elderly pts and in those with heart disease
   - low dose for dx procedures
   - large doses for thryoid ablation in managment of thyrotoxicosis due to toxic adenoma ot toxic multinodular goiter
   - used to remove remaining thyroig tissue after thyroidectomy b/c of thyroid cancer
3. SE
   - hypothyroidism usually develops

Question 8

Propanolol

Answer 8

1. MOA
   - dec signs and sx of hyperthyroidism (tremor, tachycardia, anxiety, heat intolerance, and sweating)
   - dec T4 conversion to T3 by the liver,- reduces potency of the circulating thyroid drug
   - must be used with other anti-thyroid drugs
2. Indications
   - used when preparing for surgery and waiting for thioamde derivatives or radioactive iodine to take effect
   - combined with thioamides- rarely given alone
3. CI
   - asthma or airway disease- causes bronchoconstriction
   - Diabetics- prolong or enhance hypoglycemia by interfering with glycogenesis, and mask signs of hypoglycemia (esp tachycardia, palpitations, and tremors)
   - calcium channel blockers such as verapamil may be used if propranolol is CI