Thyroid Drugs Flashcards
What is Levothyroxine (T4) used to treat?
Hypothyroidism
Why is Levothyroxine (T4) the agent of choice for thyroid replacement and suppression therapy?
It is stable, low cost, lacks allergenic protein, and has LONG HALF LIFE permitting once daily administration.
What is Liothyronine (T3) used to treat?
Hypothyroidism
Which more potent, Levothyroxine or Liothyronine?
Liothyronine is 3-4 times more potent.
Does Liothyronine have a long or short half life?
Short half life, requiring multiple doses.
Is Liothyronine recommended for routine replacement therapy?
No.
Which class of chemical compounds is used to treat Hyperthyroidism?
Thiamides
What are the 2 thiamides used to treat hyperthyroidism?
Methimazole and propylthiouracil.
Which is more potent, methimazole or propylthiouracil?
Methimazole is 10 times more potent.
Is the half life of methimazole and propylthiouracil long or short?
Short plasma half-life.
What is the major contraindication for Thiamides?
Pregnancy.
What is the major action of Thiamides?
They prevent hormone synthesis by inhibiting thyroid peroxidase. They also block iodine organification.
Do Thiamides have a fast or slow onset of action?
Slow because synthesis rather than release of hormones is affected. Requires depletion of T4.
What are the adverse effects of Thiamides?
Nausea, GI distress. Infrequently can cause agranulocytosis.
What is Potassium perchlorate used to treat?
Hyperthyroidism
What is the action of Potassium perchlorate?
It is an anion inhibitor. Competitively inhibits iodide transport.
What is the major contraindication for Potassium perchlorate?
It is rarely used due to its association with aplastic anemia.
What is the action of Iodides?
Inhibit hormone release; inhibit organification; Decrease size and vascularity of the hyper plastic gland.
What are the contraindications to the use of Iodides?
They delay onset of thioamide therapy and prevent use of radioactive iodine due to increase in iodide tissue stores. It also crosses the placenta.
What is the action of Radioactive iodine?
It destroys the thyroid parenchyma.
What is the contraindication to radioactive iodine?
Pregnancy.
What is the treatment for radioactive contamination?
Sodium iodide. It competes out radioactive iodine.
What is the action of Propranolol?
It is a beta blocker. Blocks the beta adrenergic receptor.
What is Propranolol an effective adjunctive therapy for?
Thyrotoxicosis.
What does Propranolol help alleviate?
It alleviates the effects of excess thyroid hormone on the heart and circulation.
What are the effects of Propranolol?
Reduces breathing rate, excessive sweating, heat intolerance, nervousness and anxiety.
True or false: Propranolol affects thyroid hormone levels.
False. Propranolol DOES NOT affect thyroid hormone levels.
What is Graves disease?
It is the most common form of hyperthyroidism. TSH receptor activating antibodies are developed.
What is Thyroid Storm?
A sudden acute exacerbation of all of the symptoms of thyrotoxicosis.
What are the causes of Thyroid storm?
Discontinuing needed hyperthyroid medication; over replacement of thyroid hormone; recent treatment with radioactive iodine; severe infection, illness, or stress in a hyperthyroid patient.
What is the treatment for Thyroid Storm?
Hospitalization; Decrease circulating thyroid hormone levels and decrease their formation. Use PTU or methimazole to decrease thyroid hormone. Use Na iodide or K iodide to inhibit thyroid hormone. Control heart rate by propranolol.
Explain the hypothalamic-pituitary-thyroid axis.
Hypothalamus secretes thyrotropin releasing hormone (TRH). TRH stimulates synthesis and release of thyrotropin (TSH). TSH increases the synthesis and release of T4 and T3.
What is the effect of stress on the thyroid.
Stress induces hypothyroidism because it is a negative regulator of the hypothalamus.
