Thyroid and Anti-Thyroid Drugs

Question 1

thyroid hormone preparations (hypothyroid)

Answer 1

• synthetic levothyroxine !!!
• liothyronine
• liotrix
• dessicated thyroid

Question 2

how to administer thyroxine

Answer 2

• empty stomach, 30-60 mins before bfast or 3 hours after dinner
• can double after skipped
• same manufacturer

Question 3

factors that affect dosing and absorption for levothyroxine

Answer 3

increased req

• pregnancy
• gi disorder
• other drugs
• selenium deficiency, cirrhosis

dec req

• aging
• androgen therapy

Question 4

monitor tsh after ___
full relief of symptoms at ___
reassess dose at ___

Answer 4

monitor: 6-8 weeks
relief: 3-6 mos
reassess: 6 mos or euthyroid

Question 5

another indication to start levothyroxine

Answer 5

management of thyroid cancer (tsh suppression)

Question 6

summary of antithyroid drugs (hyperthyroid)

Answer 6

thionamides: propylthiouracil, methimazole/ thiamazole, carbimazole
iodides: potassium iodide, lugol’s solution

radioactive iodine (rai)

others: anion inhibitors, beta adrenergic blockers, glucocorticoids, lithium

Question 7

moa stages of antithyroid drugs

Answer 7

• iodides and anions: iodide transport
• thionamide: oxidation and coupling
• iodides and lithium: colloid resorption and release

Question 8

what are thionamides

Answer 8

• doc!! doc for thyroid storm!!
• propylthiouracil, methimazole, carbimazole
• preferentially iodinated
• slow onset of actions (3-4 weeks)

Question 9

moa of thionamides

Answer 9

• inhibit tpo-mediated steps: organification!, coupling

- inhibit peripheral conversion to t4 and t3

Question 10

methimazole vs ptu

Answer 10

methimazole: doc

ptu: doc for thyroid storm, first trimester, DONT GIVE WITH METHIMAZOLE
- can inhibit peripheral t4 to t3 conversion

Question 11

methimazole monitoring

Answer 11

• repeat ft4 and t3 every 2-6 weeks

- euthyroid = dec 30-50%, repeat ft4 and t3 every 4-6 wks

Question 12

what is remission for hyperthyroid

Answer 12

normal tsh, ft4, and t3 for 1 year after discontinuation of atds

Question 13

adrs of antithyroid drugs

Answer 13

• cutaneous (pruritic rash)
• auto-immune (lupus-like)
• drug induced liver injury
• granulocytopenia, agranulocytosis (rare)

Question 14

moa of iodides

Answer 14

• inhibit active transport of iodide into thyroid gland (wolff-chaikoff effect)
• major action: inhibit hormone release by reducing hormone proteolysis
• dec size and vascularity of thyroid gland

Question 15

what is potassium iodide

Answer 15

• thyrotoxic symptoms improve in 2-7 days
• iodine escape after 2-8 weeks (not for long term use)
• withdrawal = severe thyrotoxicosis
• avoid chronic use in pregnancy

Question 16

moa of anion inhibitors

Answer 16

block iodide uptake through competitive inhibition of iodide transport mechanism

Question 17

what are anion inhibitors

Answer 17

• perchlorate
• pertechnetate
• thiocyanate

Question 18

moa of beta-adrenergic inhibitors

Answer 18

• blocks sympathetic adrenergic effects of hyperthyroidism (heart)
• more peripheral effects

Question 19

what are beta-adrenergic inhibitors

Answer 19

• propanolol

- CONTRAINDICATED IN ASTHMA AND COPD

Question 20

moa of corticosteroids

Answer 20

• inhibits peripheral conversion of t4 to t3
• immunosuppression
• antipyretic

Question 21

moa of lithium

Answer 21

• inhibit thyroid hormone secretion

- does not interfere with accumulation of radioiodine

Question 22

moa of rai

Answer 22

• destroy iodine-avid tissue

Question 23

what is rai

Answer 23

• treatment of thyrotoxicosis
• 123I or 131I
• indications: hyperthyroidism and thyroid cancer

Question 24

how to administer rai

Answer 24

• pretreat with methimazole
• optimize medical therapy for comorbids
• follow up every 2-4 weeks post therapy
• initiate levothyroxine when hypothyroid

Question 25

avoid rai use in

Answer 25

children, pregnant women, intending to get pregnant (6 mos)