Thyroid Flashcards
Most common hyperthyroid etiology
Graves dz
Hyperthyroid “Definitive” tx
- Thionamides (PTU, methimazole)
- RAI
- Surgery (mostly cancer, amiodarone tox)
Hyperthyroid “Adjunctive” tx
- beta blockers (sx control)
- Steroids (block T4–> T3 conversion)
Thionamides MOA
- Inhibit thyroid hormone synthesis by interfering with thyroid peroxidase-mediated iodination of tyrosine residues in thyroglobulin
- PTU also blocks formation in liver
Thionamides Indications
- Palliative tx of hyperthyroid or adjunct to surgery/RAI
- Management of thyrotoxic crisis
Thionamides Pearls
- 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
Thionamides Monitoring
- 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***
Thionamides ADRs
- Both agents: arthralgias, rash, GI intolerance, agranulocytosis
- PTU: vasculitis, elevated LFTs, #3 cause of drug-induced acute hepatic failure**
Radioactive Iodine (RAI)
- 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***
B-Blockers for Hyperthyroidism
- Propranolol vs. metoprolol
- Used to alleviate palpitations and tachy** (most common) until thionamides take action
- Taper once hyperthyroid resolves
Steroids for Hyperthyroid
- Dexamethasone
- Prevents peripheral conversion of T4–> T3
- Long term use ass with adrenal insufficiency
Pregnancy and Hyperthyroidism
- Thionamides Category D but…
- Trying to get pregnant/1st tri: PTU
- 2nd/3rd tri: methimazole (ass with aplasia cutis)
What are 3 common etiologies of hypothyroidism?
- Hashimoto’s thyroiditis
- Thyroidectomy for hyperthyroidism or cancer
- Prior RAI therapy
What is the drug of choice for hypothyroidism?
Levothyroxine (LT4)
- replacement or supplemental therapy in congenital or acquired hypothyroidism
What is Levothyroxine MOA?
- 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
Describe the Pk of Levothyroxine.
- 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
There are 4 clinical pearls for Levothyroxine.
- Protect it** - fragile drug affected by heat, light, humidity
- Consistent dose timing**
- alone on empty stomach 30min prior to breakfast OR
- at bedtime 4hr after last meal - DEC dose 50% when converting PO to IV
- Sx resolution takes 2-3wk after starting Levo
How frequently can you increase the Levo dose if required?
q4-6wk**
If necessary, INC by 12.5-25mcg/day
In general terms, what should you understand regarding Levo dosing and Cardiac RF?
- 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
How do you dose Levo for an obese patient?
There’s a shit ton of obese people in America. Especially in the dirty south.
Use calculated lean body weight**
- reduce risk of overdose
How frequently should you monitor TSH levels?
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
There are 3 groups of drugs that can decrease the effect of LT4. What are they and how do you manage this?
- Amiodarone, PTU
- monitor thyroid function - Antacids, Ca2+, Fe, bile acid resins, fiber
- separate doses in time - CBZ, phenytoin, Rifampin
- monitor thyroid function
Describe two ADRs that may occur with overtreatment of Levo?
- S/S of hyperthyroidism
- Heart disease pt –> may induce cardiac arrhythmias, angina or AMI
- TH INC HR & Contractility –> myocardial O2 demand, which may precipitate ACS or a dysrhythmia**
What effect may Levo have on your BONES?
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
What is the T3/T4 combo drug?
Liotrix
- use for very nuanced situations
- e.g. pt who cannot convert T4 –> T3
What is Thyroid USP?
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
