Thyroid Drugs

Question 1

Properties of Levothyroxine

Answer 1

Pure T4
Slower onset but longer duration of action
Converted to T3 in body

Question 2

Uses for Levothyroxine

Answer 2

Orally effective
Primary thyroid replacement
Given IV in myxedema coma

Question 3

Name drug that is pure T3

Answer 3

Liothyronine

Question 4

Properties of Liothyronine

Answer 4

Pure T3
Rapid onset, shorter half-life
4X more potent than T4

Question 5

Therapeutic uses for Liothyronine

Answer 5

Orally effective
Not used for chronic care
Sometimes used after surgery for thyroid cancer to maintain suppressive effects while patients are being tapered off

Question 6

Name of drug that is pure T4

Answer 6

Levothyroxine

Question 7

Classification of Propylthiouracil (PTU)

Answer 7

Thioamide - Anti-Thyroid drug

Question 8

MOA of Propylthiouracil

Answer 8

Inhibits peroxidase enzyme therefore inhibits synthesis of TH

Takes weeks for effects due to TH stores in body

PTU also inhibits conversion of T4 to T3

Question 9

Classification of Methimazole

Answer 9

Thioamide

Anti-TH

Question 10

MOA of Methimazole (MMI)

Answer 10

Inhibits perozidase enzyme therefore inhibits TH synthesis

Takes weeks to be effective due to TH stores

Question 11

Therapeutic use of Thiomides

Answer 11

Non-destructive inhibition of Thyroid
Therapy is about 1 year
If hyperthyroidism recurrs - usually surgery

Question 12

PK of Thioamines

Answer 12

Absorbed well orally
Rapid clearance, and concentrated in thyroid
Metabolized by conjugation and urine excretion

PTU - less potent than MMI and more doses daily

Question 13

Adverse effects of Thioamides

Answer 13

Agranulocytosis - rare, in first few months, sxs are sore throat and fever, treat aggressively with ABx

Skin rash, drug fever, arthralgia, myalgia

Overdose - hypothyroidism

MMI can produce fetal toxicity

PTU causes liver toxicity - RARE

Question 14

MMI vs PTU

Answer 14

MMI usually drug of choice
-not during 1st trimester of pregnancy

PTU
-use during thyroid storm

Question 15

Pharmacological effects of Iodides

Answer 15

Inhibitionof TH synthesis and release - faster acting

Do not inhbit conversion of T3 to T4

Question 16

Uses of Iodides

Answer 16

Used during thyroid storm
Used last 10 days before thyroidectomy (clean and safe)
DO NOT use before radioiodine therapy
Used in radiation emergencies to copete with released radioactive iodine

Question 17

MOA of Radioactive iodine

Answer 17

Weak beta radiation, used for localized tissue destruction

Question 18

Uses and effects of Radioactive iodine

Answer 18

Small doses for dx of hyperthyroidism

Larger doses for thyroid tissue destruction
Orally effective
No damage to other tissues

Question 19

Contraindications of Radioactive iodine

Answer 19

Pregnancy, breastfeeding, and young children.