Lecture 38: Thyroid Disorders Flashcards by Brooke Thornburg

Thyroid Tests for adults

-TSH
-Free T4
-ATgA (autoimmune)
-TPO-Ab (autoimmune)
-TRAb (autoimmune)

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TSH test

-pituitary TSH level
-0.5-5.0 mlU/L
-gold standard

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Free T4 test

-direct measurement of free thyroxine
-0.7-1.9 ng/dL
-most accurate

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ATgA test

-antibodies to thyroglobulin
-positive in autoimmune thyroid disease
-undetectable in remission

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TPO-Ab test

-thyroperoxidase antibodies
-more sensitive of the 2 antibodies

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TRAb test

-thyroid receptor stimulating antibody
-confirms Grave’s disease

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Drug induced HYPERthyroidism cause

-excessive thyroid supplementation:
-iodinated compounds
-amiodarone (>250mcg)
-interferons a and B
-Lithium

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HYPERthyroidism Treatment

-thioamides
-radioactive iodine (RAI)
-Surgery (thyroidectomy)

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Thioamide drugs

-Propylthiouracil
-Methimazole** preferred

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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

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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

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Propylthiouracil (PTU) dosing

-initial: 50-150mg TID
-maintenance: 50mg BID or TID
-maximal: 1,200mg/day

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Methimazole dosing

-initial: 5-40mg/day depending on Free T4
-maintenance: 5-10mg/day
-maximal: 60mg/day

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Methazole initial dosing

-1-1.5xULN: 5-10mg/day
-1.5-2: 10-20mg/day
->2: 20-40mg/day

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Thioamide side effects

-GI upset
-Rash (macropapular or wheals/hives)
-Agranulocytosis
-Hepatitis

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Thioamide maculopapular rash

-no systemic systems
-treat w diphenhydramine/other antihistamines
-may try another thioamide

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Thioamide Wheals, hives, SOB side effect

-type I anaphylactoid
-50% cross reactivity
-must use RAI or surgery

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Agranulocytosis

-low dangerous white blood cell count
-immunocompromised
-flu symptoms, mouth sores look out for
-reversible, discontinue thioamides

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Hepatits

-obtain baseline LFT and PRN
-disc thioamides, give RAI or surgery

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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

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Thioamide remission rate

-40% after 1-2 years
-80% after 5-10 years

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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