tyroid

1. Thyroid Hormones and Related
Drugs

2. Thyroid Hormones and Related Drugs
• Produce two thyroid hormones (both are
lipid soluble).
– Thyroxine (tetraiodothyronine or T4).
– Triiodothyrronine (T3).
• Produce the hormone calcitonin (CT).
– Regulates calcium homeostasis.
– CT inhibits the action of osteoclasts.
– CT accelerates the uptake of calcium and
phosphates into the bone matrix.

3. • Actions Of Thyroid Hormones
– Increase basal metabolic rate (BMR)
– Stimulates synthesis of Na+ / K+ ATPase
– Calorigenic effect.
• Helps to regulate body temperature.
– Regulate metabolism
• Protein synthesis.
• Increase the use of glucose and fatty acids for ATP.
• Increase lypolysis.
• Accelerate body growth, especially of the nervous system.
• Enhances actions of the catecholamines (norepinephrine and
epinephrine).
– In hyperthyroidism there is an increased heart rate, more forceful
heartbeats, and increased blood pressure.

4. THYROID HORMONES
T3 and T4

5. Synthesis of thyroid hormones
Materials : iodine & tyrosine
1. Iodide is trapped by sodium-iodide symporter
2. Iodide is oxidized by thyroidal peroxidase to iodine
3. Tyrosine in thyroglobulin is iodinated and forms Monoiodotyronine
(MIT) & diiodotyronine (DIT)
4. Iodotyrosines condensation: MIT+DIT→T3; DIT+DIT→T4
5. Release of thyroid hormones (5T4:1T3) after proteolysis
6. Peripheral T4 to T3 conversion
– Deiodinase cleaves the iodine at position 5 to yield triiodithronine, T3

6. Thyroid hormone excess and deficit
• Hyperthyroidism
– Palpitations
– Heat intolerance
– Tachycardia
– Diaphoresis
– Nervousness
– Weight 
• Increased appetite
– Scanty menses
– Exophthalmos
–  TSH
• Hypothyroidism
– Fatigue
– Cold Intolerance
– Dry skin, coarse hair
– Lethargy
– Weight 
• Anorexia
– Heavy menses
– Hoarse voice
–  TSH

7. HYPOTHYROIDISM
Deficiency in Thyroid Hormones
• Three types:
– Primary = abnormal thyroid gland unable to perform one of
its many functions **most common**
– Secondary = pituitary gland dysfunctional & does not
secrete TSH
– Tertiary = reduced secretion of thyrotropin-releasing
hormone (TRH) from hypothalamus  decreased TSH 
decreased thyroid hormone levels

8. HYPOTHYROIDISM
Lab values
• Increased TSH
• Decreased T4
• Decreased T3 (does not correlate well)
Cretinsim – hypothryoidism from pregnancy
Myxedema – hypothryoidism during adult years

9. HYPOTHYROIDISM
Treatment
• Not curative, only palliative
• Thyroid agents are given to replace what
thyroid gland itself cannot produce

10. HYPOTHYROIDISM
Medications
• Levothyroxine
– Most common
– Chemically pure
– Longer half-life so only need qd
– Preferred agent b/c hormonal content is standardized
and effect is predictable
• Liothyronine
– Chemically pure
– Rapid onset
– Short duration of action
– Used mainly when rapid effect or rapidly reversible
effect needed (dx procedures)
– Not likely to be used for long-term administration

11. HYPOTHYROIDISM
Liotrix
• Synthetic T3-T4 combination
• Not drug of choice due to lack of uniformity, purity & formulation
stability
• Oldest form
• Least expensive

12. HYPOTHYROIDISM
Common Medication Side Effects:
• Tachycardia, palpitations, angina, dysrhythmias, hypertension,
cardiac arrest
• Insomnia, tremors, H/A, anxiety
• Nausea, diarrhea, increased/decreased appetite, cramps
• Menstrual irregularities, weight loss, sweating, heat intolerance,
fever, thyroid storm

13. HYPERTHYROIDISM
• Excess in circulating thyroid hormone
• Caused by diffuse toxic goiter (Graves’ Disease), toxic multinodular
goiter, toxic uninodular goiter and excessive doses of levothyroxine
• Relatively common condition
• Much more likely to occur in women

14. HYPERTHYROIDISM
Lab Values
• Increased TSH
• Increased Free T4 – most useful
• Increased T3 – not usually ordered

15. HYPERTHYROIDISM
Treatment
• Aimed at either the cause or symptoms
– Antithyroid drug
– Beta-blockers
– Iodides
– Ionic inhibitors
– Radioactive isotopes of iodine (RAI)
– Surgical intervention
• Goal of tx
– Correct hypermetabolic state with minimum of
side effects and with smallest incidence of
hypothyroidism

16. ANTITHYROIDS

17. HYPERTHYROIDISM
• Beta-blockers
– Inhibit adrenergic effects of excess thyroid hormone
– Excellent for prompt, symptomatic relief but no
intrinsic antithyroid activity
– Symptom control within days so excellent choice of 1st
line therapy and pre-operative tx
– Must be used in conjunction w/ other tx modalities for
definitive control of persistent disease
– Particularly valuable for minimizing cardiac
complications of hyperthyroidism (i.e. Atrial
Fibrillation, angina)
– Propanolol most widely used beta-blocker for this
condition

18. HYPERTHYROIDISM
Antithyroid Agents
• Methimazole & propylthiuracil (PTU)
– most widely used
– Act by inhibiting the incorporation of iodine
molecules into the amino acid tyrosine, a process
required to make precursors for T3 & T4.
• This impedes formation of thyroid hormone
– Propylthiouracil has added ability to inhibit T4 to
T3 conversion in peripheral circulation
– Neither drug can inactivate existing thyroid
hormone
– Brings about overall decrease in thyroid hormone
level & normalizes overall metabolic rate

19. HYPERTHYROIDISM
Antithyroid Agents
• Not curative, only palliative
• Used to prevent surge in thyroid hormones occurring after surgical
tx or during RAI (radioactive iodine) therapy
• Long-term administration (over years) may induce spontaneous
remission however most patients eventually require surgical
intervention or RAI

20. HYPERTHYROIDISM
Antithyroid Agents
• Side Effects:
– Most serious = liver & bone marrow toxicity
– Drowsiness, H/A, vertigo, fever, parasthesias, N/V,
diarrhea, jaundice, hepatitis, loss of taste, smoky
colored urine, decreased urine output,
agranulocytosis, leukopenia, thrombocytopenia,
lymphadenopathy, bleeding, rash, pruritis,
hyperpigmentation, myalgia, arthralgia, nocturnal
muscle cramps, BUN & serum creatinine increased,
enlarged thyroid, nephritis

21. Thank you!!!