Thyroid hormones and analogues MCQs With Answer provide B. Pharm students a focused review of thyroid physiology, pharmacology, therapeutic analogues and clinical management. This set emphasizes key keywords: thyroid hormones, T3, T4, levothyroxine, liothyronine, liotrix, deiodinase, thyroid receptor isoforms (TRα/TRβ), pharmacokinetics, drug interactions, adverse effects and dosing considerations. Questions cover mechanisms of action, synthetic analogues, transporters (MCT8), antithyroid agents, radioactive iodine, monitoring (TSH, free T4), special situations (pregnancy, myxedema coma, thyroid storm) and receptor-selective thyromimetics. The content is concise yet thorough to build clinical and dispensing competence. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which hormone is the primary prohormone secreted by the thyroid gland?
- Triiodothyronine (T3)
- Thyroxine (T4)
- Reverse T3 (rT3)
- Calcitonin
Correct Answer: Thyroxine (T4)
Q2. Which thyroid hormone is considered the biologically active form at the nuclear receptor?
- Thyroxine (T4)
- Triiodothyronine (T3)
- Reverse T3 (rT3)
- Thyroglobulin
Correct Answer: Triiodothyronine (T3)
Q3. Which enzyme is primarily responsible for peripheral conversion of T4 to T3?
- Thyroid peroxidase (TPO)
- Sulfotransferase
- 5′-deiodinase
- Monoamine oxidase
Correct Answer: 5′-deiodinase
Q4. What is the approximate elimination half-life of levothyroxine in an adult?
- Approximately 7 days
- Approximately 24 hours
- Approximately 12 hours
- Approximately 2 hours
Correct Answer: Approximately 7 days
Q5. Which synthetic analogue is essentially synthetic T3 and used when rapid replacement is needed?
- Levothyroxine
- Liothyronine
- Liotrix
- Methimazole
Correct Answer: Liothyronine
Q6. Thyroid hormones primarily exert their effects by which mechanism?
- Activation of membrane G-protein coupled receptors
- Binding to cytosolic enzyme complexes
- Modulation of mitochondrial electron transport
- Binding to nuclear thyroid hormone receptors and altering gene transcription
Correct Answer: Binding to nuclear thyroid hormone receptors and altering gene transcription
Q7. Which transporter is crucial for thyroid hormone entry into neurons and other cells?
- NIS (sodium-iodide symporter)
- MCT8 (monocarboxylate transporter 8)
- OATP1B1
- P-glycoprotein
Correct Answer: MCT8 (monocarboxylate transporter 8)
Q8. Which antithyroid drug inhibits thyroid peroxidase and also inhibits peripheral 5′-deiodinase?
- Methimazole
- Propylthiouracil (PTU)
- Radioactive iodine (I-131)
- Levothyroxine
Correct Answer: Propylthiouracil (PTU)
Q9. Which preparation contains a fixed mixture of T4 and T3 in a 4:1 ratio?
- Levothyroxine
- Liothyronine
- Liotrix
- Thyroid USP (desiccated thyroid)
Correct Answer: Liotrix
Q10. Which laboratory test is most sensitive for monitoring and adjusting levothyroxine therapy?
- Total T3
- Total T4
- TSH (thyroid-stimulating hormone)
- Thyroglobulin
Correct Answer: TSH (thyroid-stimulating hormone)
Q11. How does levothyroxine affect warfarin anticoagulant response?
- Decreases warfarin effect by inducing clotting factors
- Increases warfarin effect by enhancing degradation of clotting factors
- No interaction
- Causes unpredictable interaction
Correct Answer: Increases warfarin effect by enhancing degradation of clotting factors
Q12. Which long-term adverse effect is most associated with excessive thyroid hormone replacement in elderly patients?
- Hypoglycemia
- Osteoporosis and increased fracture risk
- Severe bradycardia
- Pulmonary fibrosis
Correct Answer: Osteoporosis and increased fracture risk
Q13. Concurrent ingestion of which supplement significantly reduces oral levothyroxine absorption?
- Vitamin C
- Calcium supplements
- Folic acid
- Acetaminophen
Correct Answer: Calcium supplements
Q14. Radioactive iodine (I-131) therapy is contraindicated in which situation?
- Non-toxic multinodular goiter in elderly
- Pregnancy
- Mild subclinical hyperthyroidism
- Post-thyroidectomy hypothyroidism
Correct Answer: Pregnancy
Q15. Which deiodinase isoenzyme predominantly produces reverse T3 (rT3) from T4?
- Type 1 deiodinase (D1)
- Type 2 deiodinase (D2)
- Type 3 deiodinase (D3)
- Thyroid peroxidase (TPO)
Correct Answer: Type 3 deiodinase (D3)
Q16. Which thyroid receptor isoform is the primary target for liver-mediated lipid effects of thyromimetics?
- TRα
- TRβ
- TRγ
- TRδ
Correct Answer: TRβ
Q17. Which selective thyroid hormone receptor agonist has been investigated as a lipid-lowering thyromimetic (TRβ-selective)?
- Levothyroxine
- Liothyronine
- Sobetirome (GC-1)
- Methimazole
Correct Answer: Sobetirome (GC-1)
Q18. Which antithyroid drug is generally preferred during the first trimester of pregnancy due to lower teratogenic risk?
- Methimazole
- Propylthiouracil (PTU)
- Radioactive iodine (I-131)
- Levothyroxine
Correct Answer: Propylthiouracil (PTU)
Q19. Approximately what is the plasma half-life of liothyronine (synthetic T3)?
- About 1 day (≈24 hours)
- About 7 days
- About 6 hours
- About 2 weeks
Correct Answer: About 1 day (≈24 hours)
Q20. An increased reverse T3 with low T3 but normal TSH typically indicates which condition?
- Primary hyperthyroidism
- Euthyroid sick syndrome (non-thyroidal illness)
- Primary hypothyroidism due to thyroidectomy
- Graves’ disease
Correct Answer: Euthyroid sick syndrome (non-thyroidal illness)
Q21. Which test is most sensitive for detecting early primary hypothyroidism?
- Serum total T4
- Serum total T3
- Serum TSH
- Thyroid ultrasound
Correct Answer: Serum TSH
Q22. How should levothyroxine therapy be initiated in an elderly patient with ischemic heart disease?
- Full replacement dose immediately
- Start at low dose and titrate slowly
- Administer only IV doses
- Do not use levothyroxine in elderly
Correct Answer: Start at low dose and titrate slowly
Q23. What is the typical laboratory pattern in primary hyperthyroidism?
- High TSH and high T4
- Low TSH and high T4
- Low TSH and low T4
- Normal TSH and low T4
Correct Answer: Low TSH and high T4
Q24. Diffuse increased uptake on a radioiodine uptake scan is most consistent with which diagnosis?
- Subacute thyroiditis
- Graves’ disease
- Toxic multinodular goiter
- Thyroid cyst
Correct Answer: Graves’ disease
Q25. Which serious hematologic adverse effect is classically associated with methimazole therapy?
- Agranulocytosis
- Hemolytic anemia
- Thrombocytosis
- Eosinophilia
Correct Answer: Agranulocytosis
Q26. Which medication provides rapid symptomatic control of adrenergic features in thyroid storm?
- Propranolol
- Levothyroxine
- Methimazole
- Radioactive iodine (I-131)
Correct Answer: Propranolol
Q27. Which laboratory measurement best reflects the biologically active circulating thyroid hormone available to tissues?
- Total T4
- Free T4
- Total T3
- Thyroglobulin
Correct Answer: Free T4
Q28. Mutations in which thyroid hormone transporter are associated with severe neurodevelopmental delay and movement disorders (Allan-Herndon-Dudley syndrome)?
- NIS (sodium-iodide symporter)
- MCT8 (monocarboxylate transporter 8)
- TPO (thyroid peroxidase)
- DIO2 (deiodinase type 2)
Correct Answer: MCT8 (monocarboxylate transporter 8)
Q29. Preoperative administration of high-dose potassium iodide (Lugol’s solution) before thyroidectomy primarily acts by which mechanism?
- Stimulates thyroid hormone synthesis
- Inhibits thyroid hormone release and reduces gland vascularity
- Blocks TSH receptors permanently
- Enhances iodide uptake to increase radioiodine efficacy
Correct Answer: Inhibits thyroid hormone release and reduces gland vascularity
Q30. Which clinical scenario most commonly warrants use of IV liothyronine and/or levothyroxine for urgent thyroid hormone replacement?
- Subclinical hypothyroidism without symptoms
- Myxedema coma (severe hypothyroid crisis)
- Mild postpartum hypothyroidism
- Hyperthyroidism due to Graves’ disease
Correct Answer: Myxedema coma (severe hypothyroid crisis)
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