Endocrine: Thyroid Flashcards
TRH
thyrotropin releasing hormone
TSH
thyroid stimulating hormone
T3, T4
circulating thyroid hormones
low T3 and T4…
sends signal to hypothalamus to release TRH
TRH activates…
pituitary to release TSH, stimulating thyroid to produce more t3 and t4.
graves disease
TSH antibodies mimic TSH, stimulate T3 and T4 production.
pituitary adenomas
excessive TSH secretion that doesnt respond to T3 negative feedback
toxic adenoma
leads to thyroid nodules
drug induced hyperthyroid disorder
excessive thyroid hormone dosage
or amiodarone tx
presentation of hyperthyroid
weight loss heat intolerance goiter fine hair tachy warm/moist skin anxiety insomnia
hyperthyroid: diagnostics
elevates t4
suppressed TSH
radioactive iodine uptake
thyroid antibodies
radioactive iodine uptake in hyperthyroidism
elevated if thyroid gland is actively and excessively secreting T4/T3.
tx for hyperthyroid
ablation
thiouereas
nonselective b blockers
iodines/iodides
2 examples of thioureas
methimazole (MMI)
propylthiouracil (PTU)
thiourea MoA
inhibits iodination and synth of thyroid hormones.
PTU will also block t3/t4 conversion in periphery.
thiourea onset of action
4-6 weeks. slow.
which is more potent, MMI or PTU?
MMI by 10x.
pregnant patients and thioureas
PTU in 1st tri
switch to MMI for 2nd and 3rd
AE thioureas
hepatotoxicity arthralgia fever rash agranulocytosis
black box: PTU
hepatotoxicity
methimazole (MMI) dose
15-60mg/day in 3 divided doses
onset methimazole
12-18 hr
protein binding PK/PD
none
metabolism of PK/PD
hepatic
PTU dosing
initial & maintenance
initial: 300 mg/day in 3 doses
maintenance: 100-150mg/day in 3 doses.
onset PTU
24-36hr
protein binding: PTU
high. 80-85%
metabolism of PTU
hepatic
Nonselective B blocker for hyperthyroid
propranolol
propranolol MoA for hyperthyroid
blocks manifestations mediated by B adrenergic receptors
can block conversion of t4 to t3.
nonselective B blockers in hyperthyroid are
primarily for symptom relief
AE of b blockers for hyperthyroid
Brady
hypoTN
dizzy
cardiac ischemia
blackbox: nonselective B blocker for hyperthyroidism
cardiac ischemia
Iodines/Iodides
drug
lugol solution
potassium iodide
MoA Iodines/iodides
inhibits release of stored thyroid hormone and can reduce vascularity of gland prior to surgery
when is iodine/iodide used?
before surgery
after ablation
or thyroid storm
AE iodine/iodide
metallic taste
hypersensitivity
burning mouth
thyroid storm
life threatening decompensated thyrotoxicosis
causes of thyroid storm
trauma
infection
noncompliance c meds
severe inflammation of thyroid
thyroid storm presentation
fever tachy dehydrated coma delirium tachypnea
tx of thyroid storm
PTU or MMI
PTU and MMI as initial tx for thyroid storm
give loading doses, then around the clock
in thyroid storm, when should iodide be started?
1 hour after PTU
symptom control in thyroid storm
b blocker
acetaminophen for fever
corticosteroids
corticosteroids for thyroid storm
IV loading dose
then around the clock x 1-3 days.
hypothyroid disorders (4)
hashimoto
iatregenic
iodine deficiency
secondary causes
Hashimoto disease
autoimmune-induced thyroid injury characterized by decrease in thyroid secretion
iatrogenic hypothyroid
thyroid resection
iodine deficiency
most common cause of hypothyroidism
secondary causes of hypothyroidism
pituitary insufficiency drug induced (amiodarone, lithium)
drugs that cause hypothyroid
amiodarone
lithium
hypothyroid presentation
cold weight gain fatigue bradycardia slow reflexes dry skin coarse hair
hypothyroid diagnostics
low T4
elevated TSH
presence of thyroid abs
who should be screened for hypothyroid? and how?
patients >60 y.o
thyroid panel
tx for hypothyroid
levothyroxine
levothyroxine MoA
synthetic T4
dosing of hypothyroid
1.6 mcg/kg/day
which bodyweight to use for levothyroxine?
ideal
titrate levothyroxine based off of
T4
TSH
onset of action: levothyroxine
3-4 days oral
6-8 hr IV
peak therapeutic effect of levothyroxine
4-6 wks
protein binding of levothyroxine
> 99%
metabolism of levothyroxine
hepatic metabolism to T3
elimination of levothyroxine
urine
levothyroxine monitoring
monitor TSH q4-8wks after initiation/change
AE levothyroxine
hyperthyroidism
cardiac
inc risk fractures
myxedema coma
life threatening decompensated hypothyroidism
causes of myxedema coma
trauma
infection
HF
drug induced
drugs which can induce myxedema
narcotics
anesthesia
lithium
amiodarone
myxedema coma presentation
not always coma
AMS, hypoventilation, hypothermia
tx of myxedema
iv thyroid hormone replacement
empiric abx
corticosteroids
IV hormone replacement in myxedema
loading dose of IV levothyroxine then
large daily dose until PO meds are tolerated
abx in myxedema
empiric if infection is suspected
corticosteroids in myxedema
q8 hydrocortisone
normal TSH
0.5 - 4.5
normal T4
0.8 - 1.9
low TSH, high T4
hyperthyroid
high TSH, low T4
hypothyroid