Lecture 38: Thyroid Disorders Flashcards
Thyroid Tests for adults
-TSH
-Free T4
-ATgA (autoimmune)
-TPO-Ab (autoimmune)
-TRAb (autoimmune)
TSH test
-pituitary TSH level
-0.5-5.0 mlU/L
-gold standard
Free T4 test
-direct measurement of free thyroxine
-0.7-1.9 ng/dL
-most accurate
ATgA test
-antibodies to thyroglobulin
-positive in autoimmune thyroid disease
-undetectable in remission
TPO-Ab test
-thyroperoxidase antibodies
-more sensitive of the 2 antibodies
TRAb test
-thyroid receptor stimulating antibody
-confirms Grave’s disease
Drug induced HYPERthyroidism cause
-excessive thyroid supplementation:
-iodinated compounds
-amiodarone (>250mcg)
-interferons a and B
-Lithium
HYPERthyroidism Treatment
-thioamides
-radioactive iodine (RAI)
-Surgery (thyroidectomy)
Thioamide drugs
-Propylthiouracil
-Methimazole** preferred
Propylthiouracil facts
-1-2.5 hour half life
-q8-12h
-blocks T4 to T3 conversion
-do not use if lactating
-less potent
-preferred in first trimester then switch to methimazole
Methimazole facts
-6-9 hour half life
-qd
-start after 16 weeks pregnancy
-10x potent
-acute pancreatitis side effect
-use PTU for first trimester then switch
preferred drug of choice if patient is not pregnant
Propylthiouracil (PTU) dosing
-initial: 50-150mg TID
-maintenance: 50mg BID or TID
-maximal: 1,200mg/day
Methimazole dosing
-initial: 5-40mg/day depending on Free T4
-maintenance: 5-10mg/day
-maximal: 60mg/day
Methazole initial dosing
-1-1.5xULN: 5-10mg/day
-1.5-2: 10-20mg/day
->2: 20-40mg/day
Thioamide side effects
-GI upset
-Rash (macropapular or wheals/hives)
-Agranulocytosis
-Hepatitis
Thioamide maculopapular rash
-no systemic systems
-treat w diphenhydramine/other antihistamines
-may try another thioamide
Thioamide Wheals, hives, SOB side effect
-type I anaphylactoid
-50% cross reactivity
-must use RAI or surgery
Agranulocytosis
-low dangerous white blood cell count
-immunocompromised
-flu symptoms, mouth sores look out for
-reversible, discontinue thioamides
Hepatits
-obtain baseline LFT and PRN
-disc thioamides, give RAI or surgery
Thioamide efficacy monitoring
-/T4, T3, TSH initially until euthyroid
-use w minimal dose of medication
-then /Q3-6 months while on thioamides
-TSH can be misleading - remain suppressed after T4 and T3 normalize
Thioamide remission rate
-40% after 1-2 years
-80% after 5-10 years
ONce disc thioamide,
-/Q4-6 weeks for first 3-4 months
-then yearly after
Radioactive Iodine (RAI) 131I
-slow destruction of thyroid w isotope
-capsule dissolved in water
-colorless and tasteless
-avoid physical contact and secrection >5days
RAdioactive Iodine warnings
-DO NOT USE IN PREG, LAC, PLANIING PREG < 6 months
-avoid physical contact and secretion >5days
-euthyroid delayed (3-6 months)
-hypothyroidism likely
-WORSENS Graves orbitopathy
Thyroidectomy recommended for
-large glands (obstructive)
-mulitnodular goitor
-cancer
-med failure
-ophtalmophathy
-pregnacy 2nd trimester
Thyroidectomy risks
-vocal cord damage
-removal of parathyroid glands
Thyroidectomy monitoring
-evaluate 2 months post-surgery
B-blockers for Hyperthyroidism
-short term symptom relfief
-use in pt w HR>90bpm
-prefer cardio selective B-blockers to maintain HR 60-90 bpm
B-Blocker drugs for hyperthyroidism
-Atenolol (25-100mg qd)
-Metoprolol (25-50mg BID)
-Propranolol (10-40mg q6 or q8
-partially blocks peripheral T4 to T3 conversion bust slow onset (7-10 days) propranolol only?
Alternatives to B-blockers for hyperthyroidism
-Calcium channel blockers
calcium channel blocker drugs
-Diltiazem
-Verapamil
Avoid B-blocker agents w intrinsic sympathomimetic activity
-dont use acebutolol, cartelol, penbutol, pinbutol
HYPOthyroidism metabolic state
HYPOmetabolic
Drug-induced HYPOthyroidism caused by
-Amiodarone
-Lithium
-Interferons
HYPOthyroidism replacement therapy recommendation
-LEVOTHYROXINE (T4) first choice in all patients`
Levothyroxine black box warning
-weight loss at high doses
Levothyroxine mech
-peripheral T4 to T3 conversion
-provides hormone w/o bolus effects of T3
-long half life allows daily dosing
-25-300mcg
Levothyroxine (T4) counseling
-empty stomach (before breakfast OR
-bedtime 4 hours after dinner
Levothyroxine drug interactions cause by
-dec T4 absorption
-inc T4 requirement
-inc serum TBG concentration
-disease-drug interaction
drugs that dec T4 absorption
-DRUG INTERACTION w LEVOTHYROXINE (T4)
-bile acid sequestrants
-antacids
-ferrous sulfate
-sucralfate
-calcium supplements
drugs that inc T4 requirement
-DRUG INTERACTION WITH LEVOTHYROXINE (T4)
-enzyme inducers
-pheytoin
-carbamazepine
-rifampin
-phenobarbital
Drugs that inc serum TBG concentration
-DRUG INTERACTION w LEVOTHYROXINE (T4)
-estrogen
Disease-drug interaction w Levothyroxine (T4)
-Warfarin
Liothyronine (T3)
-rapid absorption of T3 can cause hyperthyroid symptoms = cardiac toxicities
-short t1/2 = BID-QID
-more expensive
Liothyronine (T3) use
-short-term hormone replacement
-diagnostic agent in T3 suppression test
Desiccated Thyroid USP
-natural from pork thyroid glands
-unpredicatble potency (based on iodine content) result in over- and under- supplementation
-no justification to use this product!!
Risks of desiccated thyroid USP
-allergic reaction to animal protein
Hypothyroidism efficacy monitoring
-Normal TSH and FT4 monitor q6-8 weeks after any dose change
-until TSH normalized then q3-6months for first year then yearly
-reversal of signs/symptoms in 2-3 weeks
-anemia, hair, skin changes may take 6 months
-maintain euthyroid state
Pregnancy HYPOthyroidism treatment
-LEVOTHYROXINE
-essential to continue throughout pregnancy
-require higher dose (T4 turnover prenatal vitamin?)
-+/-25mcg, TSH qtrimester
-resume to pre-preg dose after birth
-re TSH in 6-8 weeks
Patients might experience high TSH despite levothyroxine dose because of:
-poor adherence
-drug-food interaction
-drug-drug interaction
HYPOthyroidism lab values
-high TSH
-low free T4
-low T3
HYPERthyroidism lab values
-LOW TSH
-high free T4
-high T3
Levothyroxine (T4) dose
-healthy: 1.6mcg/kg/day
-elderly: same but start at 25-50mcg/day
-CVD: start 12.5-25mcg/day
-inc dose 12.5-25 mcg q6-8 weeks if TSH high
