Exam 3: L27 Thyroid Drugs Flashcards
What is the primary hormone used for thyroid hormone replacement?
Levothyroxine sodium (Levothroid®, Synthroid®)
Levothyroxine is the drug of choice for treating hypothyroidism.
What are the synthetic and porcine combinations of thyroid hormones?
Levothyroxine; Liothyronine (synthetic, Thyrolar®)
Levothyroxine; Liothyronine (Porcine, Armour Thyroid®)
These combinations include both T4 and T3.
Name two inhibitors of thyroid hormone synthesis.
- Propylthiouracil (PTU)
- Methimazole (Tapazole®)
These drugs are used to manage hyperthyroidism.
What is the role of TSH in thyroid function regulation?
Stimulates uptake of iodide, synthesis of thyroglobulin, iodination of tyrosine, and secretion of T3 and T4
TSH is released from the anterior pituitary in response to TRH from the hypothalamus.
What are the symptoms of hypothyroidism?
- Slow metabolic rate
- Weight gain
- Hypothermia
- Slow speech
- Poor memory
- Bradycardia
- Sensitivity to cold
- Lethargy
- Dry skin
- Puffiness of hands and face
These symptoms reflect the subnormal amount of thyroid hormone.
What is myxedema coma?
A severe presentation of hypothyroidism leading to decreased mental status and hypothermia
It is a medical emergency with a high mortality rate.
What are the major therapeutic agents discussed in the lecture?
- Thyroid hormones
- Antithyroid drugs
- Beta-blockers
Each group has specific mechanisms, pharmacokinetics, and clinical applications.
How does levothyroxine sodium function in the body?
It is the sodium salt of T4, producing normal levels of both T3 and T4
Its effect depends on peripheral deiodinase activity.
What characterizes hyperthyroidism?
- High metabolic rate
- Increased temperature
- Sensitivity to heat
- Tachycardia
- Emotional instability
- Increased appetite with weight loss
These symptoms reflect excess thyroid hormone activity.
Fill in the blank: The mechanism of action of thioamides includes the inhibition of _______.
[thyroid hormone synthesis]
What is the half-life of T4?
5-7 days
It takes 25-35 days to produce steady-state changes in T4 concentrations.
What are the adverse effects of thyroid hormone therapy?
- Cardiac palpitations
- Tachycardia
- Angina pectoris
- Tremor
- Weight loss
- Insomnia
- Heat intolerance
These symptoms resemble hyperthyroidism.
What are some drug interactions with thyroid hormones?
- Estrogen
- Salicylates
- Sympathetic stimulants
- Iodides
- Lithium
- Antacids
- Phenytoin
- Warfarin
These interactions can affect the efficacy and metabolism of thyroid hormones.
What are the common causes of hyperthyroidism?
- Graves’ disease
- Toxic nodular goiter
Graves’ disease is characterized by activating antibodies to the TSH receptor.
True or False: T3 is 3-5 times more active than T4.
True
What is the relationship between iodide levels and thyroid hormone production?
- High iodide inhibits hormone production
- Low iodide increases hormone production
Chronic low iodide can lead to goiter due to increased TSH levels.
What is the significance of the T3 receptor?
It is a DNA binding protein that mediates the actions of T3 and T4
Binding leads to the synthesis of messenger RNA and protein.
What is the treatment approach for hypothyroidism?
Administer thyroid hormones; lifelong therapy is often necessary
Dose adjustments may be needed for patients with other conditions.
What are the effects of thyroid hormones on metabolism?
- Increase in carbohydrate, fat, and protein metabolism
- Increase in basal metabolic rate
They also have direct effects on enzymes involved in metabolism.
What is the primary cause of secondary hypothyroidism?
TSH deficiency due to pituitary tumors or postpartum infarctions
TSH concentrations are very low in secondary hypothyroidism.
What can cause myxedema coma?
Severe hypothyroidism, often triggered by trauma, infection, or inadequate preparation for surgery
Treatment should be initiated based on clinical suspicion.
What is toxic adenoma?
A result of focal and/or diffuse hyperplasia of thyroid follicular cells whose functional capacity is independent of regulation by TSH
It may present as a solitary nodule or multinodular goiter.
What are the common presentations of patients with toxic adenoma?
Palpable thyroid nodule(s) corresponding to increased radioactive iodine concentration on thyroid scintigraphy
Some cases (3-10%) may be thyroid cancer.
What is thyroid storm?
A potentially fatal thyrotoxic crisis that can occur in hyperthyroid patients following trauma, infection, radioactive iodine treatment, or inadequate preparation for surgery.
List symptoms of thyroid storm.
- Hyperthermia
- Dehydration
- Vomiting and diarrhea
- Extreme tachycardia with arrhythmias
- Syncope
- High-output heart failure
- Behavioral changes
- Coma
What are the treatments for thyroid storm?
- Sedation
- Oxygen administration
- Antithyroid medication
- Iodine
- Corticosteroids
- Fluids and electrolytes
- β-blockers
How can hyperthyroidism be treated?
Surgically or pharmacologically, directed at reducing overproduction of thyroid hormone.
What are the surgical options for treating hyperthyroidism?
- Surgery to remove some or all of the thyroid gland
- Radioactive iodine (131I) to destroy the gland
What are the consequences of thyroidectomy and radioactive iodine treatment?
- Generally result in hypothyroidism
- Risk of thyroid storm with radioactive iodine
- Risks of surgery with thyroidectomy
What is the first line of treatment for Graves’ disease?
Pharmacological treatment
What are the mechanisms of action of antithyroid drugs?
- Inhibit thyroid hormone synthesis
- Modify peripheral effects of thyroid hormone
What are the two main thioamide derivatives used in treating hyperthyroidism?
- Methimazole (Tapazole®)
- Propylthiouracil (PTU)
What is the primary mechanism of action of methimazole?
Inhibit the synthesis of thyroid hormone in the thyroid gland
What are the indications for using Propylthiouracil (PTU)?
- Used when methimazole is intolerable
- May be used in pregnancy (especially 1st trimester)
- For patients with severe liver injury
What are common side effects of thioamide drugs?
- Itching
- Skin rash
- Granulocytopenia
- Agranulocytosis
What is the mechanism of action of potassium iodide in hyperthyroidism treatment?
Excess iodide decreases synthesis of T3 and T4 and rapidly decreases release of thyroid hormone.
What is the primary indication for radioactive iodine (131I)?
Hyperthyroid patients who cannot tolerate surgery.
What are the adverse effects of radioactive iodine treatment?
Hypothyroidism usually develops after treatment.
What is the mechanism of action of Propranolol in hyperthyroidism?
Decreases signs and symptoms of hyperthyroidism and reduces peripheral conversion of T4 to T3.
What are the contraindications for using Propranolol?
- Patients with obstructive airway disease or asthma
- Caution in diabetics
Fill in the blank: The most common side effects of thioamide drugs are _______.
[itching and skin rash]
