Thyroid

Question 1

Most common hyperthyroid etiology

Answer 1

Graves dz

Question 2

Hyperthyroid “Definitive” tx

Answer 2

• Thionamides (PTU, methimazole)
• RAI
• Surgery (mostly cancer, amiodarone tox)

Question 3

Hyperthyroid “Adjunctive” tx

Answer 3

• beta blockers (sx control)

- Steroids (block T4–> T3 conversion)

Question 4

Thionamides MOA

Answer 4

• Inhibit thyroid hormone synthesis by interfering with thyroid peroxidase-mediated iodination of tyrosine residues in thyroglobulin
• PTU also blocks formation in liver

Question 5

Thionamides Indications

Answer 5

• Palliative tx of hyperthyroid or adjunct to surgery/RAI

- Management of thyrotoxic crisis

Question 6

Thionamides Pearls

Answer 6

• Methimazole > PTU bc QD, efficacious at low doses, better with RAI, major ADRs rare
• PTU should be used in thyroid storm
• Large dose early, lower dose once controlled

Question 7

Thionamides Monitoring

Answer 7

• Check TSH and FT4 at 4-6 weeks (TSH still may be suppressed)
• Can start taper at 4-8 wks
• Remission: 12-18 mo
• 1/3 achieve complete remission, 50% recurrence rate of hyperthyroid***

Question 8

Thionamides ADRs

Answer 8

• Both agents: arthralgias, rash, GI intolerance, agranulocytosis
• PTU: vasculitis, elevated LFTs, #3 cause of drug-induced acute hepatic failure**

Question 9

Radioactive Iodine (RAI)

Answer 9

• I-131
• MOA: destroys thyroid over weeks-months
• Indications: hyperthyroid state
• Pts will need lifelong LT4
• ADRs: radiation thyroiditis–> lower neck pain–> thyroid storm possible –> pre-tx of thionamide helps
• STAY AWAY from other people for a week***

Question 10

B-Blockers for Hyperthyroidism

Answer 10

• Propranolol vs. metoprolol
• Used to alleviate palpitations and tachy** (most common) until thionamides take action
• Taper once hyperthyroid resolves

Question 11

Steroids for Hyperthyroid

Answer 11

• Dexamethasone
• Prevents peripheral conversion of T4–> T3
• Long term use ass with adrenal insufficiency

Question 12

Pregnancy and Hyperthyroidism

Answer 12

• Thionamides Category D but…
• Trying to get pregnant/1st tri: PTU
• 2nd/3rd tri: methimazole (ass with aplasia cutis)

Question 13

What are 3 common etiologies of hypothyroidism?

Answer 13

1. Hashimoto’s thyroiditis
2. Thyroidectomy for hyperthyroidism or cancer
3. Prior RAI therapy

Question 14

What is the drug of choice for hypothyroidism?

Answer 14

Levothyroxine (LT4)

• replacement or supplemental therapy in congenital or acquired hypothyroidism

Question 15

What is Levothyroxine MOA?

Answer 15

• T4 converted to active compound T3 via deiodination in the liver and peripheral tissues
• TH exerts its metabolic effects through control of DNA transcription and protein synthesis

Question 16

Describe the Pk of Levothyroxine.

Answer 16

• half life = ~ 7d** = steady state usually takes 4-6wk [it will take time for the pt to see improvements]
• narrow therapeutic window**
• 80% of PO is absorbed in SI

Question 17

There are 4 clinical pearls for Levothyroxine.

Answer 17

1. Protect it** - fragile drug affected by heat, light, humidity
2. Consistent dose timing**
   - alone on empty stomach 30min prior to breakfast OR
   - at bedtime 4hr after last meal
3. DEC dose 50% when converting PO to IV
4. Sx resolution takes 2-3wk after starting Levo

Question 18

How frequently can you increase the Levo dose if required?

Answer 18

q4-6wk**

If necessary, INC by 12.5-25mcg/day

Question 19

In general terms, what should you understand regarding Levo dosing and Cardiac RF?

Answer 19

• healthy young patient start higher dose
• older adults who may have CV disease cut dose in half
• (+) RF or CAD history cut dose in half again

Be careful not to dose too high and give pt massive dysrhythmia or MI

Question 20

How do you dose Levo for an obese patient?

There’s a shit ton of obese people in America. Especially in the dirty south.

Answer 20

Use calculated lean body weight**

- reduce risk of overdose

Question 21

How frequently should you monitor TSH levels?

Answer 21

TFTs should be assessed ~ 6wk after initiation and at dose adjustments.

TSH levels may not be achieved for 6-8wk

Once euthyroid, can monitor TSH at 6-12 mo intervals

Question 22

There are 3 groups of drugs that can decrease the effect of LT4. What are they and how do you manage this?

Answer 22

1. Amiodarone, PTU
   - monitor thyroid function
2. Antacids, Ca2+, Fe, bile acid resins, fiber
   - separate doses in time
3. CBZ, phenytoin, Rifampin
   - monitor thyroid function

Question 23

Describe two ADRs that may occur with overtreatment of Levo?

Answer 23

1. S/S of hyperthyroidism
2. Heart disease pt –> may induce cardiac arrhythmias, angina or AMI
   - TH INC HR & Contractility –> myocardial O2 demand, which may precipitate ACS or a dysrhythmia**

Question 24

What effect may Levo have on your BONES?

Answer 24

Osteoporosis

• esp w/elderly pt
• overt HYPERthyroidism may result in bone loss… pt treated with LT4 have subclinical hyperthyroidism which can lead to decreased bone density
• osteoclasts are stimulated more

Question 25

What is the T3/T4 combo drug?

Answer 25

Liotrix

• use for very nuanced situations
• e.g. pt who cannot convert T4 –> T3

Question 26

What is Thyroid USP?

Answer 26

Armour Thyroid

• thyroid extract from pigs (actual thyroid levels vary a lot)
• may lead to supraphysiologic levels of T3
• people may feel better on Armour Thyroid cause it gets ya High