Thyroid drugs

Question 1

process of thyroid hormone production

Answer 1

iodide is needed to produce thyroid hormones

hypothalamus will secrete thyroid releasing hormone (TRH) to the pituitary gland, which will then secrete thyroid stimulating hormone (TSH) to the thyroid gland. thyroid gland will secrete t3 and t4 (circulates mostly as t4 but active form is t3)

Question 2

lab report for primary hypothyroidism

Answer 2

TSH high

t4 low

Question 3

lab report for primary hyperthyroidism

Answer 3

TSH low

t4 high

Question 4

lab report for secondary hypothyroidism

Answer 4

TSH low

t4 low

Question 5

lab report for secondary hyperthyroidism

Answer 5

TSH high

t4 high

Question 6

treatment for hypothyroidism (2 main drugs)

Answer 6

levothyroxine and liothyronine

Question 7

emergency related to thyroid imbalance

Answer 7

thyrotoxicosis (due to too much thyroid hormone) leading to thyroid storm

causes adrenergic hyperactivity

Question 8

indications for levothyroxine

Answer 8

used for treatment of hypothyroidism (oral form) and myxoedema coma (IV form)

Question 9

contraindications for levothyroxine

Answer 9

• those with subclinical hypothyroidism
• elderly
• pregnant
• those with ischemic heart disease

Question 10

indications for liothyronine

Answer 10

used via IV for treatment of myxoedema coma (severe hypothyroidism)

Question 11

comparisons between levothyroxine and liothyronine (3 basis)

Answer 11

apart from its use, these 2 drugs differ in:

1. administration
   - levo = oral or IV
   - lio = IV
2. onset time
   - levo = 3-5 days for oral and 6-8 hours for IV
   - lio = 3 hours
3. half-life/excretion
   - lio is excreted via urine after 1-2 days
   - levo is excreted via urine after 1 week

Question 12

general causes of hypothyroidism

Answer 12

1. failure of thyroid gland itself
   - autoimmune antibodies attack the thyroid (e.g. hashimoto disease)
   - iodine deficiency
   - drugs like amiodarone
2. failure of pituitary gland
   - pituitary failure
   - hypothalamic failure

Question 13

general causes of hyperthyroidism

Answer 13

1. failure of thyroid gland itself
   - autoimmune (grave’s disease)
   - hyperactive thyroid nodules
2. body problem
   - iodine excess
   - inappropriate release of stored thyroid hormones

Question 14

treatment for thyroid storm

Answer 14

first step: lower thyroid levels by giving propylthiouracil or iodine (preferred as it can additional prevent release of stored t3/t4)

additional step: can give beta blockers to prevent adverse effect of thyrotoxicosis on the heart

Question 15

side effects of levothyroxine and liothyronine (long term)

Answer 15

in the long term, high dose levo/lio can increase bone resorption = osteoporosis (especially in post-menopausal women)

Question 16

lab report for subclinical hypothyroidism

Answer 16

TSH high

t4 normal

Question 17

lab report for subclinical hyperthyroidism

Answer 17

TSH low

t4 normal

Question 18

treatment for hyperthyroidism

Answer 18

• thioamides (carbimazole and propylthiouracil)
• iodine (lugol’s solution)
• radioactive iodine (123 and 131)

Question 19

carbimazole and propylthiouracil (drug class, MOA and uses)

Answer 19

Drug class: thioamide

MOA: inhibits thyroid peroxidase enzyme and interfere with iodination = no thyroid hormone production

Uses:

• treat hyperthyroidism
• treat thyroid storm (P>C as it has additional effect to prevent t4 to t3 conversion)
• treatment before thyroidectomy

Question 20

side effects of carbimazole and propylthiouracil

Answer 20

most important adverse effect: agranulocytosis (red flag if the patient develops fever/infection)

Question 21

specific contraindications for propylthiouracil

Answer 21

propylthiouracil has can cross placenta and risk goiter in fetus but compared to carbimazole has a more serious risk of fatal abnormalities, it is advised to take propylthiouracil in the 1st trimester while organogenesis is occurring. in the 2-3rd trimester (after organs are formed), switch to carbimazole to prevent hepatotoxicity in mother

Question 22

lugol’s solution (drug class, MOA and uses)

Answer 22

Drug class: iodide

MOA: inhibit t3/t4 release from stored tissues + decreases iodine uptake + prevent t3/t4 synthesis

Uses: treatment for thyroid storm and also in pre-op (to reduce thyroid gland size and vascularity around the area + reduce thyroid hormone synthesis and release)

Question 23

side effects of iodide

Answer 23

• when used long term, can cause negative feedback and exacerbate thyroid storm when suddenly taken off
• causes angioedema

Question 24

contraindications of iodine

Answer 24

contraindicated in pregnancy (can cause goiter in fetus)

Question 25

radioactive iodine 123 and 131 (drug class, MOA and uses)

Answer 25

Drug class: iodine

MOA: is taken up by thyroid follicular cells and with its gamma rays, can destroy thyroid gland without damage to surrounding tissues

Uses: 131 is for treatment, 123 is for diagnostic test to look for hot spots

Question 26

side effects of radioactive iodine

Answer 26

• hard to estimate how much to give and now has hypothyroidism

Question 27

contraindication for radioactive iodine

Answer 27

cannot be used in pregnant ladies