Thyroid gland

The thyroid is a bilobed gland which lies anterior and inferior to the larynx.

Thyroid gland location

The main functional unit of the thyroid is the follicle that consist of a single layer of epithelial cells surrounding a lumen filled with thyroglobulin, which is the storage form of thyroid hormone.

The two major thyroid hormones are triiodothyronine (T3) and thyroxine (T4)

Iodine is very important in the synthesis of thyroid hormones

TSH which is released from the pituitary gland in response to TRH from the hypothalamus regulates the synthesis of thyroid hormones.

Regulation of thyroid hormones release

Thyroid hormones: Euthyroidism: normal thyroid function(normal T3, T4 and TSH level). Hypothyroidism: inadequate secretion of thyroid hormones (low T3 and T4 and high TSH), results in: Bradycardia, poor resistance to cold, and mental and physical slowing ◦ In children, this can cause mental retardation and dwarfism

Hyperthyroidism: an excess of thyroid hormones secretion(high T3 and T4 and low TSH) causing: Tachycardia and cardiac arrhythmias, body wasting, nervousness, tremor, and excess heat production.

Thyroid hormones function:1. General metabolic effects: Increase oxygen consumption, metabolic rate, heat production (thermogenesis) it increases BMR (Basal Metabolic Rate): The amount of energy (in the form of calories) that the body needs to function while resting for 24 hours. 2. Increase glucose utilization and oxidation by muscles, increase hepatic gluconeogenesis. 3. CNS: Influence growth and development, axon proliferation, myelin sheath formation.4. CVS: Increase cardiac output and heart rate, decrease peripheral resistance. 5. G.I. tract and kidneys: Important for function, increases intestinal motility.

Treatment of hypothyroidism:

Hypothyroidism usually results from autoimmune destruction of the gland or the peroxidase

Diagnosed by elevated TSH

Condition presented at birth: Cretinism: Impaired mental and skeletal development Condition presented at adulthood: Myxedema: Muscle weakness, decreased appetite, fatigue, and lethargy

Is a synthetic thyroid hormone which is identical to the natural thyroid hormone thyroxine T4 . The human organism does not differentiate between natural T4 and synthetic b/c of their identical effects. Is converted to tri-iodo-thyronine T3 in the peripheral organs and develops its specific effect at the T3-receptor.

Levothyroxine (T4):

Levothyroxine (T4): Trade names:

Eltroxin tab : 500 mcg , 100 mcgEuthyrox tab : 50 Mg , 100 MgTherapeutic group: thyroid hormone

Hormone replacement therapy to treat hypothyroidism .It is also used to treat or prevent goiter.

Do not use these medicines if :1. You suffer from hyperthyroidism,

myocardial infarction or myocarditis2. Drug allergies3. You suffer from uncontrolled

hypoadrenalism or hypopituitarism

Special cautions: You suffer from diabetes (insulin or oral diabetes

medication doses may need to be changed when you start taking levothyroxine)

You are elderly If you have problems with your pituitary gland If you suffer from epileptic seizures as they may

occur more frequently. You suffer from heart disease, coronary artery

disease, or a history of blood clots anemia (lack of red blood cells); osteoporosis, or low bone mineral density; if you have recently had a heart attack, or are

having any symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the jaw or shoulder, nausea, sweating, general ill feeling).

Levothyroxine is not expected to harm an unborn baby. If you become pregnant while taking this medicine, do not stop taking the medicine without your doctor's advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Your dose needs may be different during pregnancy. Levothyroxine can pass into breast milk, but it

is not expected to be harmful to a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.

Changing from one levothyroxine sodium to another should be done only with personal medical consultation and with close surveillance of the patient .

How should you take levothyroxine? Do not exceed the recommended dose, (once daily) Do not share this medication with another person,

even if they have the same symptoms you have. Levothyroxine works best if you take it on an empty

stomach, at least 30 minutes before breakfast(once daily) and try to take the medicine at the same time each day.

Do not chew halve or crush the tablet Take the medicine with a full glass of water Tell your doctor if you consume soybean products

walnuts, and high-fiber foods as they may reduce the absorption of levothyroxine and the dose may be changed as a result

Discontinuation should be done gradually If you miss a dose, take it as soon as

possible(never double it)

While using levothyroxine, you may need frequent medical tests.Tell any doctor or dentist who treats you that you are using levothyroxine.Store at room temperature away from moisture and heat.It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well. Unexplained weight loss may occur while using this medicine so do not use it for this purpose

What should you avoid?avoid taking the following drugs within 4 hours before or 4 hours after you take levothyroxine:Calcium carbonateCholestyramineFerrous sulfate iron supplement;Sucralfate;Sodium polystyrene sulfonateAntacids that contain aluminum or magnesium

Levothyroxine side effects:1. Fast or irregular heart rate2. Fever, hot flashes, sweating3. Sleep problems (insomnia)4. Changes in your menstrual periods5. Vomiting, diarrhea, appetite changes, weight changes6. Nervousness heart palpitations tachycardia and intolerance to heat

Treatment of hyperthyroidism:

Excessive amounts of thyroid hormones in the circulation are associated with a number of disease states, including Graves disease, toxic adenoma, and goiter

TSH levels are reduced due to negative feedback

Treatment options:1. Removing part or all of the thyroid gland2. Inhibiting synthesis of the hormones3. Blocking release of the hormones from

the follicle

Inhibiting synthesis of the hormones:• The thioamides: propylthiouracil (PTU, Propyl-Thiocil® 50mg ) and methimazole (Mercaptizol® 20mg)

• Therapeutic group : Antithyroid• MOA: Inhibit the oxidative processes

required for iodination of tyrosyl groups and the condensation of iodotyrosines to form T3 and T4 , PTU can also block the conversion of T4 to T3

• Have no effect on the thyroglobulin already stored in the gland; clinical effects of these drugs may be delayed until thyroglobulin stores are depleted

PTU

• Do not use if you are sensitive to any of its components

• Consult your doctor if :1. if you are pregnant, planning to become

pregnant, or are breast-feeding as it may harm the baby

2. if you have allergies to medicines, foods, or other substances

3. if you have a history of blood or bone marrow problems, liver problems, kidney problems, or lung or breathing problems

How to use propylthiouracil:• Take propylthiouracil by mouth with or without

food.• Unless directed otherwise by your doctor,

space your doses evenly throughout the day.• If you miss a dose of propylthiouracil, take it

as soon as possible. If it is almost time for your next dose, take the 2 doses together, then go back to your regular dosing schedule

• Some MEDICINES MAY INTERACT with propylthiouracil. Such as:

Anticoagulants (eg, warfarin), beta-blockers (eg, propranolol), digoxin, or theophylline because the risk of their side effects may be increased by propylthiouracil

Cautions:• Do not drive as it may cause drowsiness

or dizziness• Propylthiouracil should not be used in

CHILDREN younger than 6 years old

MercoptizolActive.I : methimazole

Theu. Group : imidazole derivative contaning sulfer.

20mg – 30 TAB

can be halved , don’t chewcontraindication : liver problem

PTU and Methimazole side effects:• Relatively rare adverse effects include

agranulocytosis, rash, edema, GI side effect, dizziness and drowsiness

• PTU can cause liver toxicity or liver failure and should be reserved for patients who are intolerant of methimazole

Blocking release of the hormones from the follicle(Iodide):• MOA: Iodide inhibits the release of

thyroid hormones from thyroglobulin by unknown mechanisms

• Iodide is rarely used as the sole therapy and it is not useful for long-term therapy, because thyroid ceases to respond to the drug after a few weeks

• A pharmacologic dose of iodide inhibits the iodination of tyrosines “acute Wolff-Chaikoff effect” but this effect lasts only a few days

• Used for potentially fatal thyrotoxic crisis (thyroid storm) or prior to surgery

• Iodide is administered orally

• Adverse effects ◦ Sore mouth and throat ◦ Swelling of the tongue or larynx ◦ Rashes ◦ Ulcerations of mucous membranes ◦ Metallic taste in the mouth