thyroid drugs

Question 1

Levothyroxine (synthroid)

Answer 1

• synthetic version of T4
• converted to T3 in peripheral tissue
• DOC for hypothyroidism
• more stable: longer t1/2, longer peak to tx effect (3-4 weeks)
• adults: 50-100 micrograms/day
• children require more T4 per kg of body weight due to higher metabolism

Question 2

Liothyronine (cytomel)

Answer 2

• T3 replacement
• tx: used in combo with levothyroxine for hypothyroidism
• more rapidly effective (reaches peak in 2-4 hrs after oral admin), eliminated more quickly, less stable, more costly
• 4X as potent as levothyroxine
• IV formulation can be given in acute emergency (myxedema coma)

Question 3

precautions with thyroid hormone replacement

Answer 3

• initiate low doses in PTs with cardiovascular disorders: angina, CAD, HTN

Question 4

thioamides

Answer 4

• propylthiouracil, methimazole, carbimazole (only the 1st 2 are used in US)
• inhibit the organification of iodide and coupling of iodotyrosine (inhibit thyroid peroxidase)
• methimazole is the active metabolite of carbimazole
• can be taken orally or inserted into rectum for thyrotoxicosis

Question 5

SE of thioamides

Answer 5

• maculopapular rash
• agrunolcytosis (Methimazole is safer)
• hepatitis
• lupus-like syndrome
• PTs who develop agranulocytosis or lupus-like SEs are absolute contraindications for further antithyroid durg tx

Question 6

propylthiouracil vs. methimazole

Answer 6

• same mech of action
• methimazole has a longer half life, is excreted by slowly, is taken at lower doses and less often and has lower risk of agranulocytosis
• but Propylthiouracil is safer in pregnancy (less transplacental passage and lower concentration in breast milk)
• P for P

Question 7

radioactive iodine

Answer 7

• tx of choice for relapsed hyperthyroidism after antithyroid drug tx (or in PTs who have adverse rxns to antithyroid drugs)
• contraindications: pregnancy and breast feeding
• also, generally not used in children because it can cause irreversible hypothyroidism
• effects don’t take place for 4 weeks, use initially with beta blockers or antithryoid drugs
• can be taken orally

Question 8

beta blockers

Answer 8

• propanolol, atenolol, metoprolol, nadolol
• tx: adjuctive agents for Graves’ disease with mod-severe symptoms
• control tremor, anxiety, palpitations