Endocrine Pharmacology: Thyroid Hormones
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Questions and Answers

What is the primary action of levothyroxine?

  • Inhibits the synthesis of thyroid hormones
  • Blocks the release of thyroid hormone
  • Acts as an agonist at nuclear T3 receptors
  • Acts as a precursor to active thyroid hormone T3 (correct)

    • Which of the following medications is NOT a thyroid hormone replacement therapy?

  • Levothyroxine
  • Liotrix
  • Liothyronine
  • Methimazole (correct)

    • Which of the following drugs can increase levothyroxine metabolism?

  • Propylthiouracil
  • Phenytoin (correct)
  • Calcium carbonate
  • Iron salts

    • Which of the following conditions is NOT an indication for thyroid hormone replacement therapy?

    <p>Hyperthyroidism (B)</p> Signup and view all the answers

    What is the primary concern regarding the narrow therapeutic index of thyroid hormone drugs?

    <p>Dosage must be carefully titrated to avoid side effects (C)</p> Signup and view all the answers

    What is the mechanism of action of propylthiouracil and methimazole?

    <p>Inhibiting the synthesis of thyroid hormones (C)</p> Signup and view all the answers

    Which of the following drugs is most likely to affect the pharmacodynamic effect of levothyroxine?

    <p>Estrogen derivatives (C)</p> Signup and view all the answers

    Which of the following factors can inhibit the GI absorption of levothyroxine?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the half-life of liothyronine (T3) in a euthyroid individual?

    <p>Less than 2 days (C)</p> Signup and view all the answers

    Which of the following statements is TRUE regarding the use of thyroid hormone replacement therapy for pituitary TSH suppression?

    <p>It is used to suppress the production of TSH by the pituitary gland. (A)</p> Signup and view all the answers

    Which of the following medications is MOST likely to increase the need for warfarin dose adjustment in a patient with hypothyroidism?

    <p>Levothyroxine (D)</p> Signup and view all the answers

    Which of these is an example of a common side effect of thyroid hormone replacement therapy?

    <p>Fatigue (C)</p> Signup and view all the answers

    Which of the following drugs can inhibit peripheral deiodinase, thereby impairing the activation of T4 to T3?

    <p>Amiodarone (D)</p> Signup and view all the answers

    What is the primary reason why changing thyroid hormone preparations is not recommended?

    <p>All of the above (D)</p> Signup and view all the answers

    Which of the following drugs is primarily used to treat hyperthyroidism?

    <p>Methimazole (B)</p> Signup and view all the answers

    What is the primary mechanism of action of Iodides (KI, NaI) in the treatment of hyperthyroidism?

    <p>Blocking thyroid hormone release (A)</p> Signup and view all the answers

    What is the primary hormone synthesized by the thyroid gland that is crucial for regulating metabolism?

    <p>Thyroxine (D)</p> Signup and view all the answers

    Which medication is commonly used to treat hyperthyroidism by inhibiting the thyroid's hormone production?

    <p>Propylthiouracil (A)</p> Signup and view all the answers

    What is the mechanism of action for propranolol when used in the context of thyroid storm?

    <p>Blocks beta-adrenergic receptors (D)</p> Signup and view all the answers

    What biological process does the hypothalamus initiate to influence the production of thyroid hormones?

    <p>Secretion of releasing hormones (D)</p> Signup and view all the answers

    Which drug acts as an adjuvant treatment during a thyroid storm?

    <p>Esmolol (A)</p> Signup and view all the answers

    Which of the following statements about levothyroxine is false?

    <p>It directly inhibits thyroid hormone synthesis. (A)</p> Signup and view all the answers

    What structural feature differentiates anti-thyroid drugs from thyroid hormones?

    <p>Absence of a phenolic hydroxyl group (D)</p> Signup and view all the answers

    What is the typical action of sodium iodine when used therapeutically?

    <p>Inhibits excessive thyroid hormone production (A)</p> Signup and view all the answers

    What is the primary function of thyroid hormones T3 and T4?

    <p>Stimulate heat generation (C)</p> Signup and view all the answers

    Which factor is necessary for the synthesis of thyroid hormones?

    <p>Iodide (D)</p> Signup and view all the answers

    What effect does T3 have on catecholamine activity?

    <p>Potentiates beta effects (A)</p> Signup and view all the answers

    What happens when outer ring de-iodination of T4 occurs?

    <p>Increases hormone activity (A)</p> Signup and view all the answers

    Which statement best describes the composition of thyroid hormones?

    <p>They are derived from MIT and DIT condensation (A)</p> Signup and view all the answers

    What role do glucocorticoids play in the regulation of the HPT axis?

    <p>Inhibit the synthesis and release of TSH (C)</p> Signup and view all the answers

    What is the main use of recombinant human TSH (Thyrogen®) in clinical practice?

    <p>As a diagnostic tool for thyroid function (D)</p> Signup and view all the answers

    What physiological effect is associated with severe hypothyroidism during pregnancy?

    <p>Irreversible mental retardation (A)</p> Signup and view all the answers

    Which statement about T3 is correct?

    <p>It is 5 times more potent than T4 (A)</p> Signup and view all the answers

    What is the primary mechanism of action for thyroid hormones like T4?

    <p>They act via nuclear receptors (D)</p> Signup and view all the answers

    What is the mechanism of action of potassium iodide in treating thyroid conditions?

    <p>It inhibits multiple biosynthetic steps via negative feedback. (D)</p> Signup and view all the answers

    Which of the following is a contraindication for administering radioactive iodine (Iodotope)?

    <p>Pregnancy (A)</p> Signup and view all the answers

    Which adverse effect is associated with the use of radioactive iodine?

    <p>Bone marrow depression (A)</p> Signup and view all the answers

    What is a significant interaction when using propylthiouracil (PTU)?

    <p>Amiodarone reduces the effect of PTU. (D)</p> Signup and view all the answers

    How does fluoroborate function as an ionic inhibitor?

    <p>It competes with iodide in the transport by NIS. (D)</p> Signup and view all the answers

    What is a common side effect of potassium iodide therapy?

    <p>Metallic taste (B)</p> Signup and view all the answers

    What primary condition is treated with antithyroid drugs like methimazole?

    <p>Graves' disease (D)</p> Signup and view all the answers

    What is a notable pharmacokinetic property of propylthiouracil (PTU)?

    <p>It is rapidly absorbed with a short half-life. (A)</p> Signup and view all the answers

    What is the role of T3 in relation to T4 when binding to thyroid receptors?

    <p>T3 has a higher binding affinity to TR than T4. (D)</p> Signup and view all the answers

    In terms of competitive inhibition, which ion is NOT typically used?

    <p>Radiation-131 (B)</p> Signup and view all the answers

    Which factor is NOT listed as a regulator of thyroid function?

    <p>Glucagon (A)</p> Signup and view all the answers

    What is the primary mechanism by which thioamides such as propylthiouracil exert their therapeutic effect?

    <p>By blocking the synthesis of T4 and T3 (D)</p> Signup and view all the answers

    How does hyperthyroidism affect plasma LDL levels?

    <p>Lowers plasma LDL levels. (D)</p> Signup and view all the answers

    Which step is NOT part of the biosynthesis of thyroid hormones?

    <p>Direct conversion of T4 to T3 in plasma. (A)</p> Signup and view all the answers

    What is a common effect of thyrotoxicosis on insulin sensitivity?

    <p>Decreased sensitivity to insulin. (C)</p> Signup and view all the answers

    Which of the following is a preferred treatment approach for younger patients with hyperthyroidism?

    <p>Antithyroid drug therapy (D)</p> Signup and view all the answers

    What is the rationale for using levothyroxine in small doses in elderly patients?

    <p>All of the above (D)</p> Signup and view all the answers

    Which of the following medications is NOT considered an antithyroid drug used to treat hyperthyroidism?

    <p>Levothyroxine (A), Radioactive iodine (C)</p> Signup and view all the answers

    What is the primary goal of levothyroxine replacement therapy in patients with hypothyroidism?

    <p>Restore normal levels of thyroid hormone in the blood. (B)</p> Signup and view all the answers

    In the context of the provided information, what is the reason for the elevated TSH level in the 69-year-old man with a history of myocardial infarction and recurrent ventricular arrhythmia?

    <p>The patient's TSH level is elevated because the thyroid gland is not producing enough thyroid hormone (hypothyroidism). (A)</p> Signup and view all the answers

    Which of the following factors may influence the thyroxine dose in a patient with hypothyroidism and a history of myocardial infarction and recurrent ventricular arrhythmia?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the preferred treatment approach for hyperthyroidism in older patients with cardiac disease?

    <p>Radioactive iodine therapy (C)</p> Signup and view all the answers

    Why is levothyroxine preferred over liothyronine in the management of hypothyroidism?

    <p>Levothyroxine has a longer half-life and provides more sustained thyroid hormone replacement. (C)</p> Signup and view all the answers

    Study Notes

    Endocrine Pharmacology: Thyroid Hormone Analogs & Inhibitors

    • Thyroid hormones (T3 and T4) are crucial for metabolic processes, and their biosynthesis and regulation are crucial to understand
    • The hypothalamus-pituitary-thyroid (HPT) axis plays a vital role in this regulation by triggering hormone production
    • The hypothalamus releases TRH, which stimulates the pituitary to release TSH
    • The thyroid gland produces T3 and T4 in response to TSH
    • T3 and T4 have broad physiological effects impacting growth, development, metabolism, and cardiovascular function
    • Iodide is essential for thyroid hormone synthesis; its uptake, oxidation, and incorporation into tyrosine molecules are carefully regulated steps
    • Thyroid hormone analogs and inhibitors are used to treat hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid)
    • Hypothyroidism is treated using synthetic T3 or T4, while hyperthyroidism is treated using drugs like methimazole or propylthiouracil that inhibit T3 and T4 synthesis or block their release

    Hypothyroidism

    • Symptoms of hypothyroidism include dry skin, coarse hair, puffy face, slow heartbeat, constipation, and weight gain
    • Common treatments include desiccated thyroid, L-T4 (levothyroxine), and L-T3 (liothyronine)
    • Issues like increased clotting factor catabolism affect anticoagulants.

    Hyperthyroidism

    • Symptoms of hyperthyroidism include hair loss, bulging eyes, enlarged thyroid, sweating, rapid heartbeat, weight loss, and tremor
    • Treatments for hyperthyroidism include drugs like propylthiouracil (PTU) and methimazole (MMI) to inhibit thyroid hormone synthesis, or radioactive iodine to destroy thyroid tissue
    • Beta-blockers, like propranolol, can help to control rapid heart rate and other symptoms.

    Thyroid Hormone Synthesis and Regulation

    • The hypothalamus produces TRH to stimulate the pituitary to release TSH
    • TSH stimulates the thyroid gland to produce T3 and T4
    • Thyroid hormones exert feedback loops on both the pituitary and hypothalamus
    • Iodine is crucial for thyroid hormone synthesis
    • T3 is more potent than T4, and T3 is more active than T4

    Drugs to Treat Thyroid Hormone Deficiency

    • Levothyroxine (T4) is often the treatment
    • Liothyronine (T3) can be used in certain cases
    • Dessicated thyroid (a natural extract) is rare
    • Proper dosage and monitoring of thyroid hormone replacement are crucial; potential drug interactions can occur

    Drugs to Treat Thyroid Hormone Excess

    • Propylthiouracil (PTU)
    • Methimazole
    • Potassium iodide (KI)
    • Radioactive iodine (I-131)
    • Beta-blockers (used to manage symptoms)

    Thyroid Storm

    • Life-threatening exacerbation of hyperthyroidism
    • Elevated thyroid hormone levels, often caused by stress
    • Adjunctive therapy with drugs like propranolol to manage symptoms

    Important Considerations and Clinical Implications

    • Iodine intake affects thyroid hormone synthesis
    • Medical conditions and other medication use must be considered when dosing thyroid-related medications.
    • The doctor's monitoring is essential to adapt thyroid hormone levels

    Laboratory Tests

    • TSH (Thyroid-Stimulating Hormone)
    • T3 and T4 (free and total)
    • Thyroid-related tests must be monitored to maintain appropriate hormone levels.

    Additional Information

    • Important drug interactions with various medications
    • Specific details on different drugs (e.g., PTU, MMI) to treat both hypothyroidism and hyperthyroidism
    • Diagnostic and therapeutic management techniques are essential to consider

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    Endocrine Pharmacology: Thyroid Hormone Analogs & Inhibitors PDF

    Description

    Explore the fundamentals of thyroid hormones and their analogs in this quiz. Learn about the HPT axis, the regulation of T3 and T4 production, and the pharmacological approaches to treating thyroid disorders such as hypothyroidism and hyperthyroidism. Master the essential roles of iodide and the physiological impacts of thyroid hormones on health.

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