Thyroid drugs Flashcards
process of thyroid hormone production
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)
lab report for primary hypothyroidism
TSH high
t4 low
lab report for primary hyperthyroidism
TSH low
t4 high
lab report for secondary hypothyroidism
TSH low
t4 low
lab report for secondary hyperthyroidism
TSH high
t4 high
treatment for hypothyroidism (2 main drugs)
levothyroxine and liothyronine
emergency related to thyroid imbalance
thyrotoxicosis (due to too much thyroid hormone) leading to thyroid storm
causes adrenergic hyperactivity
indications for levothyroxine
used for treatment of hypothyroidism (oral form) and myxoedema coma (IV form)
contraindications for levothyroxine
- those with subclinical hypothyroidism
- elderly
- pregnant
- those with ischemic heart disease
indications for liothyronine
used via IV for treatment of myxoedema coma (severe hypothyroidism)
comparisons between levothyroxine and liothyronine (3 basis)
apart from its use, these 2 drugs differ in:
- administration
- levo = oral or IV
- lio = IV - onset time
- levo = 3-5 days for oral and 6-8 hours for IV
- lio = 3 hours - half-life/excretion
- lio is excreted via urine after 1-2 days
- levo is excreted via urine after 1 week
general causes of hypothyroidism
- failure of thyroid gland itself
- autoimmune antibodies attack the thyroid (e.g. hashimoto disease)
- iodine deficiency
- drugs like amiodarone - failure of pituitary gland
- pituitary failure
- hypothalamic failure
general causes of hyperthyroidism
- failure of thyroid gland itself
- autoimmune (grave’s disease)
- hyperactive thyroid nodules - body problem
- iodine excess
- inappropriate release of stored thyroid hormones
treatment for thyroid storm
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
side effects of levothyroxine and liothyronine (long term)
in the long term, high dose levo/lio can increase bone resorption = osteoporosis (especially in post-menopausal women)
lab report for subclinical hypothyroidism
TSH high
t4 normal
lab report for subclinical hyperthyroidism
TSH low
t4 normal
treatment for hyperthyroidism
- thioamides (carbimazole and propylthiouracil)
- iodine (lugol’s solution)
- radioactive iodine (123 and 131)
carbimazole and propylthiouracil (drug class, MOA and uses)
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
side effects of carbimazole and propylthiouracil
most important adverse effect: agranulocytosis (red flag if the patient develops fever/infection)
specific contraindications for propylthiouracil
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
lugol’s solution (drug class, MOA and uses)
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)
side effects of iodide
- when used long term, can cause negative feedback and exacerbate thyroid storm when suddenly taken off
- causes angioedema
contraindications of iodine
contraindicated in pregnancy (can cause goiter in fetus)
