2.1.2 AI Summary: Hypothyroidism

What is the drug of choice for hypothyroidism?

Levothyroxine

What is the onset of oral Levothyroxine?

3-5 days

What is the onset of IV Levothyroxine?

6-8 hours

What type of hormone is levothyroxine?

Synthetic T4

Why is T4 used instead of T3 in most patients?

Acts as reservoir and allows physiologic conversion

What enzyme process converts T4 into T3?

Deiodination

What are common primary causes of hypothyroidism?

Hashimoto thyroiditis, iodine deficiency, thyroid destruction

What are secondary causes of hypothyroidism?

Pituitary or hypothalamic disorders

What are treatment goals in hypothyroidism?

Normalize labs, relieve symptoms, prevent complications

What is the average full replacement dose of levothyroxine?

1.6-1.7 mcg/kg/day

What weight is used to calculate levothyroxine dosing?

Actual body weight

What is a common starting dose for mild hypothyroidism (TSH<10 mIU/L)?

25 to 50 mcg/day

Who requires lower starting doses of levothyroxine?

Elderly and cardiac disease patients

What is the typical titration increment for levothyroxine?

12.5 to 25 mcg

How often should levothyroxine doses be adjusted?

Every 6 to 8 weeks

Why must levothyroxine titration be slow?

TSH takes time to stabilize

What happens if levothyroxine dose is too high?

Hyperthyroid symptoms and cardiac risk

How behind does the change in TSH lags after starting Levothyroxine?

up to 8 weeks

How long until symptom improvement occurs after starting therapy?

2 to 3 weeks

When is maximum therapeutic effect seen?

About 6 weeks

How often should thyroid labs be monitored after changes?

Every 6 to 12 weeks

How often should stable patients be monitored?

Every 6 to 12 months

How should levothyroxine be taken for best absorption?

On empty stomach (30-60 minutes) before breakfast or 4 hours after last meals

What drugs have confliction on time to take?

biphosphonates: take levothyroxine 30 minutes after. then wait 30-60 minutes and eat breakfast

wegovy

Why are there allergic reactions to levothyroxine?

Its animal derived

Too much levothyroxine can cause what?

bone loss, heart faliure, angina, MI, afib

Which substances reduce levothyroxine absorption?

Food, calcium, iron, PPIs bile acid sequestrants

Seperate food by 30-60 minutes and medications by 4 hours

Which substances reduce production of thyroid hormone?

lithium, iodine meds (amiodarone)

Which medications increase levothyroxine metabolism?

Carbamazepine, phenytoin, rifampin, sertraline

What is the effect of estrogen?

increase circulating TBG (↓ free T4)

Thyroid binding globin

What substances decrease peripheral conversion (T4 → T3)?

BB's, amiodarone, selenium deficiency

Which conditions increase levothyroxine dose requirement?

H. pylori infection, atrophic gastritis, celiac disease

When should levothyroxine dose be higher

Hpylori infection bc drops tsh, astrophic gastritis, celiac

What is liothyronine?

Synthetic T3

Where is liothyronine most absorbed?

orally

Liothyronine disadvantages?

Higher cardiotoxicity and monitoring difficulty

What is Thyroid USP (Armour Thyroid)?

Combination T3 and T4 product

Why are natural thyroid products not recommended?

Variable potency and instability

Why are non-prescription supplements not recommended?

Products contain iodine and have risk of thyrotoxicosis

What happens to levothyroxine needs during pregnancy?

Increase by 40 to 50%

Why does pregnancy increase levothyroxine requirements?

Increased protein binding

What condition requires urgent treatment due to severe hypothyroidism?

Myxedema coma

What are symptoms of myxedema coma?

Hypothermia and decreased mental status

This is a severe medical emergency

What should be done if levothyroxine manufacturer changes?

Recheck thyroid levels

What counseling is important for levothyroxine consistency?

Maintain same formulation

When can treatment for subclinical hypothyroidism be initiated

tsh less than 10 or tsh 5-10 plus goiter/positive anti-thyroid peroxide antibodies

prior treatment with rai

symtomatic