PHARM 343 > Thyroid > Flashcards

Thyroid Flashcards

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1
Q

Primary Thyroid Disease

A

Affects Thyroid Gland (T4 and T3 secretion)

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2
Q

Secondary Thyroid Disease

A

Affects Pituitary Gland (TSH Secretion)

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3
Q

Tertiary Thyroid Disease

A

Affects Hypothalamus (TRH Secretion)

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4
Q

T4 vs T3
- Which is the main hormone secreted
- Which one is biologically active
- Which one is more protein bound
- Which one has the longer half life
- Which one is more potent

A

T4 (Thyroxine)
- Main hormone secreted
- Biologically Inactive
- 99.96% protein bound
- Half Life = 7 days (Longer half life due to being more protein bound than T3)

T3 (Triiodothyronine)
- 80% converted in periphery from T4
- Biologically Active
- 99.5% protein bound
- Half Life = 1-2 days
- 3x more potent at inhibiting TSH

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5
Q

Hyperthyroidism
- How much thyroid hormone
- Effect on metabolism

A

Too much thyroid hormone
Metabolism speeds up

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6
Q

Hypothyroidism
- How much thyroid hormone
- Effect on metabolism

A

Too little thyroid hormone
Metabolism slows down

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7
Q

TSH
- Value in Hyperthyroidism vs Hypothyroidism

A

TSH is low in Hyperthyroidism
TSH is high in Hypothyroidism

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8
Q

TSH
- Fluctuations in value

A

Will be at its highest around midnight
Will be at its lowest in late afternoon

Values are different in pregnancy and old age

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9
Q

When to use TSH

A

When screening for thyroid dysfunction
When screening for thyroid hormone replacement

Not good for pituitary diseases
- Use free T4 instead

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10
Q

When to use Free T4

A

TSH is low (Sign of hyperthyroidism)
- Use free T4 to evaluate thyrometabolic status

Use to confirm hyper/hypothyroidism
- Used as second test after TSH

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11
Q

When to use Free T3

A

Generally not used for hypothyroidism
- As T3 is usually low in absence of thyroid disease

Used to differentiate between different kinds of hyperthyroidism
- Ordered when TSH is low but T4 is normal/low

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12
Q

Who should be screened for Thyroid Disorders

A

Do not screen asymptomatic non-pregnant patients

Screen:
- Symptomatic patients
- Patients at increased risk

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13
Q

Patients at increased risk of thyroid disorders

A

Women older than 45

Postpartum Women

Patients taking lithium or amiodarone

Patients with auto immune disease
- Type 1 Diabetes
- Strong Family History

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14
Q

Tests for screening Primary Thyroid Disorders

A

TSH first

Do not use free T3 or free T4 for screening hypothyroidism or to adjust doses for patient with diagnosed primary hypothyroidism
- T3 and T4 are mostly protein bound so the amount in blood will normally be low

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15
Q

Hypothyroidism
- 2 Kinds

A

Subclinical:
- TSH high
- T4 normal

Overt:
- TSH high
- Free T4 is low

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16
Q

Hypothyroidism
- Signs and Symptoms

A

Similar to Hyperthyroidism:
- Hoarseness of Deepening of Voice
- Swelling (Goiter)
- Persistient Dry/Sore throat
- Difficulty Swallowing
- Infertility

Different from Hyperthyroidism
- Puffy Eyes
- Cold Intolerance
- Weight Gain
- Elevated Cholesterol
- Tiredness
- Forgetful/Slower thinking
- Depression
- Muscle weakness/cramps
- Slower heartbeat
- Constipation

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17
Q

Hypothyroidism
- High risk populations

A
  • Women (postpartum) - 3x more risk
  • Prior history of graves diseease
  • Increasing age (especially after 60)
  • Family history of autoimmune thyroid disease
  • Other autoimmune endocrine conditions (Type 1 diabetes)
  • Other autoimmune non-endocrine conditions (Celiac disease, Pernicious anemia)
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18
Q

Hypothyroidism
- Primary

A

Primary (99%)
- Hasimoto’s Disease
- Iatrogenic Hypothyroidism
- Iodine Excess/Deficiency
- Drugs
- Congenital

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19
Q

Hypothyroidism
- Secondary/Tertiary

A

Secondary/Tertiary (1%)
- Pituitary Disease
- Hypothalamic Disease

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20
Q

Hashimoto’s Disease

A

Primary Hypothyroidism
- Elevated Thyroid Peroxidase Antibody, attacks and impairs Thyroid Peroxidase
—> Lowers amount of thyroid hormone

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21
Q

Iatrogenic Hypothyroidism

A

Radiated Iodine
- Destroys thyroid gland
Thyroidectomy

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22
Q

What drugs cause hypothyroidism

A

Lithium
Amiodarone
Antithyroid drugs

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23
Q

Effect of Excess Iodine on Thyroid

A

Causes a surge in thyroid hormone
- Then causes white blood cells to infiltrate thyroid and impairs it from producing thyroid hormone

Causes Hypothyroidism

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24
Q

Effect of Deficiency Iodine on Thyroid

A

Hypothyroidism

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25
Hypothyroidism Treatment - Pharmacological
Levothyroxine
26
Hypothyroidism Treatment - Pharmacological Dose
Long half life, once a day dosing Dose depends on: - Age - Body weight - Pregnancy status - Cardiac Disease Severity of hypothyroidism - If subclinical = Lower dose - If RAI or Thyroidectomy = Higher dose
27
Hypothyroidism Treatment - Pharmacological Absorption
Take 30-60 minutes before breakfast with water Should be take on empty stomach - Separate by 4 hours with Iron, Calcium, Multivitamins
28
Levothyroxine Dose - Healthy Adult
1.6 mcg/kg
29
Levothyroxine Dose - Elderly (65 years or above)
1.0 mcg/kg - Average maintenance dose is 100mcg - Initiation should be at lower dose and titrated slowly (Start at 12.5-25mcg) As patient ages dose should decrease
30
Levothyroxine Dose - Cardiac Patients (Or at risk)
12.5-25mcg - Initiate at low dose and titrate slowly - Avoid cardiac compromise and ischemia (Avoid increasing BP and HR)
31
Levothyroxine - Monitoring
Primary Hypothyroidism: Monitor TSH levels Secondary Hypothyroidism: Monitor Free T4 levels Monitor every 6-8 weeks after initiation/dose change until euthyroid - Adjust as needed until values are euthyroid - Once euthyroid monitor yearly, or until new symptoms appear
32
Over treatment of Levothyroxine
- Atrial fibrillation and Stroke - Increased risk of Angina and Myocardial Infarction in Cardiac Patients - Bone Loss and Fractures - Anxiety, Sleep Disturbance, Irritability
33
Under treatment of Levothyroxine
- Increased lipids - Decreased heart rate and ventricular contractility - Increased peripheral vascular resistance and diastolic pressure - Memory loss - Mood impairment
34
Levothyroxine in Healthy Patients - Low Dose vs Full Dose (1.6 mcg/kg)
Full dose is more convenient and cost effective, achieves Euthyroidism faster
35
Hypothyroidism Treatment - Desiccated Thyroid
Lower T4:T3 ratio is lower than what is secreted by human thyroid gland - Supraphysiologic levels of T3 - Animal derivative Not recommended
36
Hypothyroidism Treatment - Liothyronine
Basically synthetic T3 - Short half life, has to be dosed twice a day - Increases Cardiac Adverse Drug Reaction
37
Hypothyroidism Treatment - Combination
Levothyroxine + Liothyronine - No evidence of benefit - Small subset of patients do better (Those that remain symptomatic on levothyroxine) Summary: Consider if patient remains symptomatic on levothyroxine - Have to carefully monitor
38
Factors that reduce Levothyroxine Effectiveness
Malabsorption Symptoms Reduced Absorption Drugs that increase clearance Factors that decrease T4 conversion to T3
39
Factors that reduce Levothyroxine Effectiveness - Malabsorption Symptoms
Short Bowel Celiac Disease
40
Factors that reduce Levothyroxine Effectiveness - Reduced Absorption
Sucralfate Food Ferrous Salts Calcium Supplements Aluminum Hydroxide Cholestyramine
41
Factors that reduce Levothyroxine Effectiveness - Drugs that increase clearance
Rifampin Carbamazepine Phenytoin
42
Factors that reduce Levothyroxine Effectiveness - Decreases T4 conversion to T3
Amiodarone
43
Hypothyroidism - Pregnancy
Thyroid function changes in pregnancy - May have to increase dose Untreated hypothyroidism can affect cognitive function of child and increase maternal hypertension, preeclampsia, postpartum hemorrhage, spontaneous abortion, fetal death
44
Hyperthyroidism - Symptoms
Similar to Hypothyroidism -- Hoarseness of Deepening of Voice - Swelling (Goiter) - Persistient Dry/Sore throat - Difficulty Swallowing - Infertility Different from Hypothyroidism - Budging eyes - Heat Intolerance - Weight Gain - Rapid/Irregular Heartbeat - Nervousness - Irritability - Frequent bowel movements - Increased sweating - First trimester miscarriage
45
Hyperthyroidism - Etiology
- Graves' Disease - Toxic Nodules - Tumours - Subacute Thyroiditis - Hashitoxicosis - Excessive Dosage of T3 or T4
46
Graves' Disease
Hyperthyroidism (Seen in younger female patients) - Body produces antibodies that activate the thyroid gland
47
Toxic Nodules
Hyperthyroidism (Seen in elderly) - Creates lots of T3 and T4 - Does not respond to negative feedback
48
Tumours
Hyperthyroidism - Excessive stimulation of thyroid gland
49
Subacute Thyroiditis
Hyperthyroidism in first phase - Then white blood cells infiltrate and damage the thyroid gland leading to hypothyroidism
50
Hashitoxxicosis
Hyperthyroidism in first phase - Then white blood cells infiltrate and damage the thyroid gland leading to hypothyroidism
51
Excessive Dosage with T3 or T4
Hyperthyroidism
52
Autoimmune Endocrine Disorders associated with Graves' Disease
- Addison's Disease - Type 1 Diabetes - Primary Gonadal Failure - Hashimoto's Thyroiditis
53
Autoimmune Non-Endocrine Disorders associated with Graves' Disease
- Celiac Disease - Myasthenia Gravis - Pernicious Anemia - Immune Thrombocytopenic purpura - Rheumatoid Arthritis
54
Hyperthyroidism - Treatment
Drugs Radioactive Iodine Surgery
55
Hyperthyroidism - Beta Blockers initiation
Used to control symptoms, should not be sole therapy - Can be initiated at presentation before diagnosis
56
Hyperthyroidism - Beta blockers For who
Considered for patients with: - Symptomatic Thyrotoxicosis - Elderly - Resting heart rate greater than 90 - Coexistent CV disease
57
Hyperthyroidism - Beta blockers which to choose
All are equally effective - Some may impair T3 to T4 conversion but has not shown to be clinically significant
58
Hyperthyroidism - Antithyroid Drugs
Propylthiouracil (PTU) Methimazole
59
Hyperthyroidism - Antithyroid Drugs Mechanism
Inhibits Thyroid Peroxidase and synthesis of thyroid hormone --> Less thyroid hormone PTU blocks peripheral T4 to T3 conversion
60
Hyperthyroidism - Antithyroid Drugs Response
Higher likelihood of response: - Older patients (Greater than 40 years old) - Small goiters - Short duration of disease - Small amounts of Thyroid Peroxidase Antibody
61
Hyperthyroidism - Antithyroid Drugs Long Term Treatment
Best to use Methimazole
62
Hyperthyroidism - Antithyroid Drugs First Line
Methimazole is preferred as first line - Except 1st trimester of pregnancy where PTU is preferred
63
PTU vs Methimazole - Half Life
Methimazole has a higher half life - Can be dosed less frequently at lower doses
64
PTU vs Methimazole - Side Effects
PTU has higher risks of side effects
65
PTU vs Methimazole - Pregnancy
Methimazole is not to be used in first trimester of pregnancy - Use PTU instead
66
Hyperthyroidism - Antithyroid Drugs Side Effects
- Skin Rash - Allergic Reaction - Agranulocytosis - Hepatotoxicity (Greater chance in PTU)
67
Hyperthyroidism - Antithyroid Drugs Counseling
Stop medication if experiencing rash, fever, jaundice, sore throat
68
Hyperthyroidism - Antithyroid Drugs Lab Tests
- Baseline CBC (Include WBC and differential) - ALT/AST - Bilirubin
69
Hyperthyroidism - Methimazole Monitoring
1. Monitor Free T4 at 4 weeks, then every 4-8 weeks (Can also add free T3) 2. Once Free T4/T3 is normal, add TSH and monitor every 2-3 months 3. Also taper dose by 30-50% 4. Continue for 12-18 months - Taper or discontinue is TSH is normal at this time
70
Long-term methimazole in Graves' disease
Hyperthyroidism has less chances to recur with long term treatment
71
Hyperthyroidism - RAI Indication
- Patient is unable to get surgery - Contraindications to ATD - Not planning to get pregnant
72
Hyperthyroidism - RAI Monitoring
Should see Euthyroidism within 6-18 weeks - 50% chance to cause hypothyroidism after 10 years
73
Hyperthyroidism - RAI Pregnancy
Contraindicated in pregnancy - Crosses placenta and destroys fetal placenta - Defer pregnancy for 3-6 months after treatment
74
Hyperthyroidism - Surgery Indication
- Symptomatic Compression - Large Goiter (greater than 80g) - Thyroid malignancy - Planning pregnancy 4-6 months or less
75
Hyperthyroidism - Surgery Recurrence
Total Thyroidectomy: 0% chance of recurrence Subtotal Thyroidectomy: 8% chance of recurrence at 5 years
PHARM 343
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