Flashcards in Thyroid Pharmacology Deck (22):
Does T3 or T4 have a shorter half life?
- T3= 1 DAY (compared to T4= 1 week)
*important because you will give T3 to someone in a hypothyroid state.
What is responsible for regulating the conversion of T4 to T3 in the periphery?
- deiodinase-1 (D1)= a peroxidase enzyme that is involved in the activation or deactivation of thyroid hormones.
*D2 is the same, but found only in the brain.
To what do T3 and T4 bind in the blood in order to be transported?
- thyroxine-binding globulin (TBG)
*tranthyretin only binds T4
How do you distinguish between primary, secondary, and tertiary HYPOthyroidism?
- PRIMARY= TH deficiency (TH levels do NOT increase with administration of TSH). Ex. Hashimotos
- SECONDARY= TSH deficiency (TSH levels do NOT increase with administration of TRH). Ex. Sheehan's
- TERTIARY= TRH deficiency (increased TSH levels with administration of TRH).
**** What is the most common drug replacement hormone for HYPOthyroidism?
- LEVOTHYROIXINE sodium (T4)
*used over liothyronine sodium (T3) bc it has a much longer half life.
Is there an advange to combining T4/T3 to treat hypothyroidism?
- not really.
What is an ADR of Levothyroixine?
- hyperthyroidism if you give too much.
What are the limited uses of Liothyronine (T3)?
- T3 suppression to differentiate hyperthyroid from euthyroidism.
- short term supppresion of a solitary thyroid nodule before radioactive iodine scan.
What is Thyrotoxicosis (hyperthyroidism); Grave's disease?
- antibody against the TSH receptor, leaing to a toxic multinodular goiter
How do you treat Thyrotoxicosis (hyperthyroidism); Grave's disease?
- inhibit thyroidal secretion via surgery or radiation.
**** How do you treat thyroid storm (potentially fatal thyrotoxic crisis)?
- sedation, O2, decrease body temp, antithyroid meds, iodine, CORTICOSTEROIDS, fluids, electrolytes, and B-BLOCKERS.
What are the antithyroid agents?
- Polythiouracil (PTU)
- Potassium perclorate (KCLO4)
- Potassium iodide (KI)
- Iodine 131
- B-adrenergic blockers (PROPRANOLOL)
**** What is Methimazole?
- inhibitor of iodine incorporation to tyrosine residues (MIT and DIT).
- preferred over PTU to treat hyperthyroidism (lower risk of liver injury).
- similar to PTU but no inhibition of T4 to T3 in periphery.
What is an ADR of Methiomazole?
**** What is Propylthiouracil (PTU)?
- same as methimazole, but also inhibits T4 to T3 in periphery.
- shorter half life than Methimazole.
What ADR does PTU have in addition to agranulocytosis (like Methimoazole)?
- severe HEPATITIS
Are Methiomazole and PTU contraindicated in pregnancy?
- YES (DO NOT USE)
What is Potassium perchlorate (KClO4)?
- interferes with Iodide transport into thyroid gland, but not used much anymore bc it can cause severe aplastic anemia.
**** What is Potassium Iodide (Lugol's solution)?
- transiently inhibits organificaiton (iodine formation).
- inhibits hormone release.
- inhibits accumulation of radioiodine.
*used as PREOPERATIVE PREPARATION for THYROIDECTOMY and for THYROID STORM.
**** What will Iodine 131 (radioactive) do?
- PERMANENTLY reduces TH production.
*mainly used for pts with Grave's disease
Why would we use a Beta blocker during thyrotoxicosis?
- to decrease hyperthyroid-induced tachycardia, tremor, sweating, heat intolerance, and anxiety.