Hypothyroidism Pharmacology Flashcards
Most common cause of hypothyroidism
chronic autoimmune thyroiditis (Hashimoto’s thyroiditis)
Pharmacology of levothyroxine
snythetic preparation of T4 → converts to T3 intracellularly
How should levothyroxine be taken for best absorption?
on empty stomach
How long does it take Levothyroxine to reach steady state?
28 days (4*half life)
what is the difference between the multiple brands of levothyroxine?
varying bioavailability → slight changes in T4
How should you treat a patient with levothyroxine to avoid variations?
continue patient on the same product
How should you dose levothyroxine in patients with CVD and the elderly?
“start low and go slow”
What levels will guide your dose adjustments of levothyroxine?
TSH and T4
adverse effects of levothyroxine
heart failure, angina, myocardial infarction
allergic or idiosyncratic reactions
osteoporosis
If you suspect your patient is allergic to thyroid hormone replacement what would you want to prescribe her?
Synthroid
Levothyroxine will interfere with drugs that:
interfere with T4 absoprtion from the gut
increases T4 clearance
blcok conversion of T4 → T3
What food/drink should a patient avoid when taking their dose of levothyroxine?
those with high fiber, soy, iron
coffee or milk
How long should you separate levothyroxine and interacting binding medications?
4 hours apart
How does liothyronine (T3) compare to levothyroxine?
3-4 times more potent
Why is liothyronine (T3) not recommended as routine replacement?
short half life
difficulty monitoring
more expensive
avoid in patients with cardiac disease
Who is the only population that uses liothyronin (T3)?
patients with polymorphism in D2 gene who are symptomatic on T4 alone
What lab values would have patient with subclinical hypothyroidism have?
normal free T4 and mildly elevated serum TSH → without obvious symptoms
When should you treat a patient with subclinical hypothyroidism?
TSH levels > 10
increased risk of devloping overt hypothyroidism if anti-thyroid peroxidase antibodies (TPOAb) are present
potential cardiac benefit in treating
What do you treat a patient with subclinical hypothyroidism with?
levothyroxine
If your hypothyroid patient becomes pregnant what should you do with her meds?
increase dose of levothyroxine ASAP → avoid overt hypothyroidism and adverse outcomes
Reference ranges for TSH and serum T4 will depend on
specific trimester in pregnancy
Signs and symptoms of myxedema coma
hypothermia, advanced stages of hypothyroid symptoms, alterd sensorium, hypoglycemia, hypoventilation
What underlying dissorders may be associated with myxedema coma?
CAD or sepsis
In myexdema coma how should the medications be administered to the patient?
parental only → no GI perstalsis
