T4 half-life
7 days
T3 half-life
0.75 day
There is more total ____ in the body, but ____ is more potent.
T4
T3
70% of thyroid hormone is bound to:
Thyroid-binding protein (TBG)
15% of thyroid hormone is bound to two different proteins (30% total):
Thyroid-binding prealbumin
Albumin
The active thyroid hormone is:
T3
Free ___ is converted to T3 by tissue _____.
Thyroxine (T4)
Deiodinases
TSH normal range:
0.5 - 2.5 microunits/L
Inverse relationship
� Less T4 = more TSH
Autoimmune hypothyroidism antibody:
Antithyroid peroxidase antibody (Anti-TPOAb) Hashimoto's Disease!!
Grave's disease antibody:
TSH receptor-stimulating antibody (TSHR-Sab)
Older thyroid studies, probably not used much:
Total thyroxine (T4)
Free T4 index
Total triiodothyronine (T3)
T3 resin uptake (T3RU)
Most common thyroid studies:
TSH (more commonly use to evaluate pt)
Free T4 (levothyroxine)
Other thyroid studies used at times:
Free thyroxine (T4)
Free triiodothyroxine (T3)
Thyroglobulin
Thyroglobulin Abs
Thyroxine-binding globulin (TBG)
Radioactive iodine uptake (RAIU)
True or false: Changes in shape or size of thyroid gland may or may not be associated with changes in secretion of thyroid hormones.
True
Hypothyroidism is higher in _____.
Whites and Hispanics, and the elderly
Hypothyroidism is lower in _____.
African Americans
Common iodine-containing drugs that can cause hypo or hyperthyroidism:
Amiodarone
Iodine
Radiocontrast media
Subclinical hypothyroidism =
TSH 2.5-10
Normal T4
No symptoms
Mild hypothyroidism =
TSH 2.5-10
Normal T4
Mild symptoms
Overt hypothyroidism levels
TSH >10
Low free T4 or T3
Pretibial myxedema
Complication of Grave's -- fluid incorporated into the tissue
Hypothyroidism symptoms include ___ skin, feeling ___, hair ____, and _____ with poor appetite.
Dry
Cold
Loss
Weight gain
Hypothyroidism symptoms including feeling ____ and ____, difficulty _____ and poor memory, and ____ voice.
Tired and weak
Concentrating
Hoarse
GI symptom of hypothyroidism:
Constipation
Gyno symptom of hypothyroidism:
Menorrhagia -- later oligomenorrhea or amenorrhea
Sensory symptoms of hypothyroidism:
Parasthesias and impaired hearing
Signs of hypothyroidism include ____ skin, ____ peripheral extremities, and _____ face, hands, and feet.
Dry, coarse
Cool
Puffy (myxedema)
Effect of hypothyroidism on the heart:
Bradycardia
Effect of hypothyroidism on reflexes:
Delayed tendon reflex relaxation
Hypothyrodism can cause ____ ____ syndrome and ____ _____ effusions.
Carpal tunnel
Serous cavity
Long-term CV consequences of hypothyroidism:
Dyslipidemia
Decreased cardiac output
Increased diastolic pressure
Hypothyroidism can cause ____ CO and ____ diastolic pressure.
Decreased
Increased
Long-term neuropsych consequences of hypothyroidism:
Dementia and depression
Hypothyroidism can cause ___ coma.
Myxedema
Hypothyroidism can cause _____ in pregnant women.
Fetal abnormalities
Use _____ in patients w/trouble converting T4-->T3 and myxedema coma.
Liothyronine (Cytomel)
Liothyronine (Cytomel)
L-isomer 3,5,5 triidothyronine
Use combined T3/T4 products in:
Patients who have difficult converting T4-->T3
Combination products:
Liotrix (Thyrolar)
Levothyroxine + Liothyronine
Dessicated thyroid
Advantages of combination products:
Improved lipid profile
Patient preference
Disadvantages of combination products:
Increase bone resorption
High serum T3 levels
Levothyroxine bioavailability variability among products:
�25%
Initial dose, adults <65 yrs:
50-100 mcg/day; do not exceed 1.6 mcg/kg/day (IBW)
Usual maintenance dose, adults <65 yrs:
1.6 mcg/kg/day (IBW)
Initial dose, adults >75 yrs:
25-50 mcg/day
Usual maintenance dose, adults >75 yrs:
1.0 mcg/kg/day
Levothyroxine cardiac ADRs:
AFib and other cardiac abnormalities
Levothyroxine other ADRs:
S/sx hyperthyroid
Depression
Osteoporosis
Drugs that decrease levothyroxine absorption:
Food, fiber, soy, enteral feedings
Calcium
Iron
Aluminum salts, sucralfate
Cholestyramine, colestipol, sodium polystyrene sulfonate
Separate drugs that decrease levothyroxine absorption by:
DDI: Drugs that increased thyroxin binding globulin
DDI: drug that increased levothyroxine clearance
DDI; Drug that impaired deiodination
2-4 hours
estrogen, raloxifene, tamoxifen
CYP inducer (CBZP, Phenytoin, phenobarbital, rifampin)
Amiodarone
May need a higher levothyroxine dose in:
Malabsorption
Pregnancy
Cirrhosis (possibly -- monitor)
May need a lower leveothyroxine dose in:
Older patients
After pregnancy
Older patients and post-pregnancy may need a ___ dose.
Lower
Malabsorption, pregnancy, and cirrhosis may need a ____ dose.
Higher
Relatively absolute contraindications to levothyroxine:
Acute MI
Adrenal insufficiency
Thyrotoxicosis
Precautions when giving levothyroxine:
Angina
Cardiac arrhythmias
Hypertension
Using for obesity
How often do you check TSH after starting levothyroxine?
6-8 weeks
Increase or decrease levothyroxine dose by ____ based on TSH.
10-20%
Whenever you increase or decrease levothyroxine dose, recheck TSH in:
6-8 weeks
How often do you check TSH in stable patients?
Every 6-12 months
Hyperthyroidism is most common among:
Women
Men and women 20-39 yrs and over 80
Secondary causes of hyperthyroidism:
TSH secreting pituitary tumor
Trophoblastic (hCG-secreting) tumors
Gestational thyrotoxicosis
Primary hyperthyroidism:
Grave's (toxic diffuse goiter)
Plummer's (toxic multinodular goiter)
Toxic thyroid adenoma
Painful subacute thyroiditis
Silent thyroiditis
Drug-induced
Subclinical hyperthyroidism=
TSH <0.1 or 0.4
Normal free T4/T3
No symptoms
Mild hyperthyroidism=
TSH <0.1 or 0.4
Normal free T4/T3
Mild symptoms
Overt hyperthyroidism=
TSH <0.1
High free T4/T3
Overt symptoms
GI symptoms, hyperthyroidism:
Weight loss or gain
Increased or decreased appetite
Diarrhea
Cardiac symptoms, hyperthyroidism:
Palpitations
Tachycardia
High output HF
AFib
Neuropsych symptoms, hyperthyroidism:
Irritability
Nervousness
Sleep disturbances
Vision changes
Fatigue
Weakness
Gyn symptoms, hyperthyroidism:
Menstrual irregularities
Eye symptoms, Grave's disease:
Exophthalmos
Proptosis
Chemosis (swelling around iris)
Conjunctival injection
Periorbital edema
Excess tearing
Corneal/optic nerve damage
Hyperpigmentation
True or false: Clubbing is a sign of Grave's disease.
True
Long-term consequences of hyperthyroidism:
Osteoporosis
Increased CV mortality and all-cause mortality
Initially control hyperthyroidism symptoms with:
Beta blockers
Temporarily diminish thyroid hormone production with:
Methimazole or (propylthiouracil if intolerant to methimazole)
**or idodide in large doses
Treatment of choice for Grave's disease:
Ablation with radioactive iodine (permanent diminish production of thyroid hormone)***
**********************************
other tx includes subtotal throidectomy (surgical removal)
********************
both require supplementation with levothyroxine
Methiomazole and propylthiouracil MOA:
Inhibit thyroid hormone production
Inhibit iodination of tyrosine residues
Inhibit T4-->T3 (PPT)
Methiomazole and propylthiouracil, common ADRs:
Hypothyroidism
Rash
Arthralgias
GI upset
Methiomazole and propylthiouracil, rare ADRs:
Agranulocytosis
Liver toxicity
PPT = rare severe hepatotoxicity
Symptoms of thyroid storm:
Fever
Tachycardia
Tachypnea
Dehydration
GI upset
Delerium, coma
Thyroid storm can be caused by:
Infection, trauma, surgery
Radioactive iodine
Antithyroid drug withdrawal
Thyroid storm treatment:
Short-acting BB (esmolol)
High dose methimazole or PPT
Iodide
Supportive care -- fluids/electrolytes, antiarrhythmics, APAP, IV corticosteroids
Levothyroxine strengths
25
50
75
88
100
112
125
137
150
175
200
300