Embedded Files
Introduction
Illustrated mechanism of action
Examples of Medication Brand Names (with Images)
Indication
Side Effects
Precautions & Contraindications
Monographs
Reference
Introduction
Introduction
Thyroid hormones are essential chemical messengers produced by the thyroid gland, a butterfly-shaped organ located in the neck. These hormones, primarily thyroxine (T4) and triiodothyronine (T3), play a crucial role in regulating the body’s metabolism, energy production, and overall growth and development.They influence almost every cell in the body by controlling how fast or slow the body’s systems work. Imbalances in thyroid hormone levels can lead to disorders such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), both of which require medical management, often including hormone replacement or suppression therapies
Illustrated Mechanism of Action
Thyroid hormones (mainly T3 and T4) exert their effects by entering target cells and binding to nuclear thyroid hormone receptors (TRs). These receptors are transcription factors that regulate gene expression.
Once bound, the hormone-receptor complex attaches to specific DNA sequences called thyroid hormone response elements (TREs), leading to increased or decreased transcription of target genes. This process ultimately affects protein synthesis, impacting basal metabolic rate, thermogenesis, heart rate, and development of the brain and skeleton.
A labeled illustration showing:
Thyroid gland → T3/T4 in blood → entry into cell
Binding to nuclear receptor → binding to DNA → protein synthesis → physiological effects
BRAND NAME
T4 Thyro
T4 Thyro
Desiccated Thyroid Extract
Eltroxin
Eltroxin
Levothyroxine
Cytomel
Cytomel
Liothothyronine
Indication
Indication
1. Hypothyroidism:
The most common indication. Thyroid hormones are used to replace the deficient hormone in patients with underactive thyroid. It helps relieve symptoms like fatigue, weight gain, and dry skin.
2. Goiter:
Thyroid hormones can be used to suppress TSH and reduce the size of an enlarged thyroid, especially if caused by iodine deficiency or high TSH levels.
3. Thyroid Cancer:
After thyroidectomy (surgical removal), thyroid hormones are given to suppress TSH, which could otherwise stimulate any remaining cancer cells.
4. Myxedema Coma:
A rare, life-threatening condition due to severe hypothyroidism. High doses of thyroid hormone are given urgently as treatment.
5. Thyroid Suppression Test:
Sometimes used diagnostically to assess thyroid nodules or gland function, though it's not commonly done nowadays
Common Side Effects
Common Side Effects
1. Palpitations – fast or irregular heartbeat
2. Anxiety or nervousness
3. Insomnia – trouble sleeping
4. Weight loss
5. Increased appetite
6. Heat intolerance – feeling hot all the time
7. Tremors – especially in the hands
8. Menstrual irregularities
9. Diarrhea
Serious Side Effects (rare):
Arrhythmias – abnormal heart rhythms (like atrial fibrillation)
Angina or heart attack – especially in elderly or heart disease patients
Osteoporosis – long-term over-treatment may lead to bone loss
These effects mostly happen when the dose is too high, leading to symptoms of hyperthyroidism. Correct dosing and regular monitoring of TSH levels help avoid these issues
Contraindications
Contraindications
1. Untreated Adrenal Insufficiency:
If a patient has low adrenal hormone levels (like in Addison's disease) and is given thyroid hormone, it can speed up metabolism and increase the body’s demand for cortisol.
Without enough cortisol, this can lead to a dangerous condition called adrenal crisis, which may cause low blood pressure, shock, and even death.
2. Thyrotoxicosis (Uncontrolled Hyperthyroidism):
Giving thyroid hormone to someone who already has too much (like in Graves' disease) can worsen symptoms like palpitations, tremors, anxiety, and may even lead to thyroid storm, a life-threatening emergency.
3. Allergy or Hypersensitivity to Ingredients:
Though rare, some patients may be allergic to levothyroxine or the inactive ingredients in the tablets (like dyes or fillers).
Relative Contraindications (Use with Caution):
1. Recent Heart Attack (Myocardial Infarction):
Thyroid hormones increase oxygen demand and heart rate.
After a heart attack, the heart is already weak, so adding stress may worsen the condition.
2. Cardiac Arrhythmias:
High doses of thyroid hormones can cause or worsen irregular heart rhythms, especially atrial fibrillation.
3. Diabetes Mellitus:
Thyroid hormones can change insulin and glucose metabolism, making it harder to control blood sugar levels.
4. Osteoporosis:
Long-term high-dose thyroid therapy increases bone turnover and can lead to bone loss, especially in postmenopausal women.
MONOGRAPH
MONOGRAPH
مستند من Dr Mohamed Hossam.pdfمستند من Dr Mohamed Hossam.pdfمستند من Dr Mohamed Hossam.pdfPage updated
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