Thyroid drugs – L-Thyroxine MCQs With Answer

Thyroid drugs – L-Thyroxine MCQs With Answer

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Introduction: Thyroid drugs, especially L-Thyroxine (levothyroxine), are central to treating hypothyroidism and related disorders. This targeted overview for B.Pharm students emphasizes pharmacology, pharmacokinetics, dosing principles, bioavailability, drug interactions, adverse effects, monitoring (TSH, free T4), and special situations such as pregnancy, pediatrics, the elderly, and myxedema coma. Topics include formulation differences, narrow therapeutic index issues, IV versus oral conversion, half‑life and steady‑state concepts, and practical counselling points like timing of administration and the impact of calcium/iron supplements. Understanding these key concepts ensures safe dispensing, rational prescribing, and effective patient counselling. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement correctly describes L‑thyroxine (levothyroxine)?

  • It is a synthetic form of triiodothyronine (T3)
  • It is a synthetic form of thyroxine (T4)
  • It is a natural extract containing T3 and T4 in equal amounts
  • It is an antagonist of thyroid hormone receptors

Correct Answer: It is a synthetic form of thyroxine (T4)

Q2. What is the approximate elimination half‑life of levothyroxine in a euthyroid adult?

  • 6–8 hours
  • 1–2 days
  • About 7 days
  • 3–4 weeks

Correct Answer: About 7 days

Q3. Which of the following agents most commonly reduces oral levothyroxine absorption?

  • Amoxicillin
  • Calcium supplements
  • Metformin
  • Furosemide

Correct Answer: Calcium supplements

Q4. What is the typical oral bioavailability range of levothyroxine tablets?

  • 10–20%
  • 35–45%
  • 70–80%
  • 95–100%

Correct Answer: 70–80%

Q5. Best patient counselling advice for timing of oral levothyroxine to maximize absorption is:

  • Take with breakfast to reduce gastric irritation
  • Take at bedtime with a glass of milk
  • Take on an empty stomach 30–60 minutes before breakfast
  • Take immediately after breakfast with coffee

Correct Answer: Take on an empty stomach 30–60 minutes before breakfast

Q6. How is levothyroxine activated in peripheral tissues?

  • Direct binding to TSH receptors
  • Conversion to T3 by deiodinase enzymes
  • Conjugation in the liver to glucuronides
  • Hydrolysis to iodide and tyrosine

Correct Answer: Conversion to T3 by deiodinase enzymes

Q7. When converting from oral to intravenous levothyroxine in severe hypothyroidism, the IV dose is approximately:

  • 25% of the oral dose
  • 50% of the oral dose
  • 75% of the oral dose
  • Equal to the oral dose

Correct Answer: 75% of the oral dose

Q8. During pregnancy, levothyroxine dose usually needs to be adjusted in which direction?

  • Decreased by about 25% due to decreased clearance
  • Increased by about 20–30% due to increased thyroid hormone requirement
  • No change is required
  • Stopped during first trimester then restarted postpartum

Correct Answer: Increased by about 20–30% due to increased thyroid hormone requirement

Q9. In myxedema coma, the recommended route of levothyroxine administration is:

  • Oral, high‑dose tablets
  • Intramuscular injection
  • Intravenous administration
  • Topical transdermal patch

Correct Answer: Intravenous administration

Q10. Which class of drugs can accelerate levothyroxine metabolism and decrease its plasma levels?

  • Proton pump inhibitors
  • H2 receptor antagonists
  • Hepatic enzyme inducers such as carbamazepine and phenytoin
  • Beta‑blockers

Correct Answer: Hepatic enzyme inducers such as carbamazepine and phenytoin

Q11. Which laboratory test is most appropriate for monitoring levothyroxine replacement in primary hypothyroidism?

  • Serum total T4
  • Serum free T3
  • Thyroid stimulating hormone (TSH)
  • Serum thyroglobulin

Correct Answer: Thyroid stimulating hormone (TSH)

Q12. The usual reference range for serum TSH in adults used to guide levothyroxine therapy is approximately:

  • 0.01–0.1 mIU/L
  • 0.4–4.0 mIU/L
  • 5–10 mIU/L
  • 10–30 mIU/L

Correct Answer: 0.4–4.0 mIU/L

Q13. Which cluster of signs suggests levothyroxine over‑replacement?

  • Cold intolerance, weight gain, dry skin
  • Bradycardia, constipation, weight gain
  • Palpitations, heat intolerance, unexplained weight loss
  • Excessive salivation, hyperpigmentation, edema

Correct Answer: Palpitations, heat intolerance, unexplained weight loss

Q14. Regarding formulation and interchangeability, levothyroxine is classified as a:

  • Wide therapeutic index drug where switching brands is unimportant
  • Narrow therapeutic index drug where consistent product use is recommended
  • Biologic product needing cold chain storage
  • Controlled substance requiring special dispensing

Correct Answer: Narrow therapeutic index drug where consistent product use is recommended

Q15. Proper storage recommendations for levothyroxine tablets include:

  • Keep frozen
  • Store in a cool, dry place away from light
  • Store in the refrigerator door
  • Keep in direct sunlight for stability

Correct Answer: Store in a cool, dry place away from light

Q16. Compared with levothyroxine (T4), liothyronine (T3) differs primarily by:

  • Longer half‑life and slower onset
  • Shorter half‑life and more rapid, potent action per microgram
  • No biological activity in humans
  • Being a prodrug converted to T4

Correct Answer: Shorter half‑life and more rapid, potent action per microgram

Q17. When switching between levothyroxine manufacturers or formulations, the best pharmacy practice is to:

  • Switch frequently to compare patient response
  • Keep the same brand or formulation consistently and monitor TSH after a change
  • Always substitute with the lowest cost generic without monitoring
  • Avoid monitoring since levothyroxine is stable across brands

Correct Answer: Keep the same brand or formulation consistently and monitor TSH after a change

Q18. Pediatric levothyroxine dosing compared to adults is typically:

  • Lower per kilogram of body weight than adults
  • Similar per kilogram as adults
  • Higher per kilogram than adults, particularly in neonates
  • Given only as intermittent high doses

Correct Answer: Higher per kilogram than adults, particularly in neonates

Q19. Which of the following commonly decreases levothyroxine absorption when coadministered?

  • Antacids containing aluminum or magnesium
  • Oral antibiotics like doxycycline having no effect
  • Topical corticosteroids
  • Vitamin C in normal dietary amounts

Correct Answer: Antacids containing aluminum or magnesium

Q20. Taking levothyroxine with coffee can result in:

  • Increased absorption and toxicity
  • No change in absorption
  • Reduced bioavailability and lower serum levels
  • Complete inactivation of the drug

Correct Answer: Reduced bioavailability and lower serum levels

Q21. How long after initiating or changing a levothyroxine dose should TSH be reassessed for steady‑state evaluation?

  • 24–48 hours
  • 1 week
  • 4–6 weeks
  • 6–12 months

Correct Answer: 4–6 weeks

Q22. After total thyroidectomy for benign disease, levothyroxine therapy should generally be:

  • Delayed for several weeks to allow healing
  • Started immediately as replacement therapy
  • Started only if TSH becomes elevated
  • Replaced with antithyroid drugs

Correct Answer: Started immediately as replacement therapy

Q23. Which antiarrhythmic drug can decrease peripheral conversion of T4 to T3, altering thyroid hormone profiles?

  • Atenolol
  • Amiodarone
  • Digoxin
  • Diltiazem

Correct Answer: Amiodarone

Q24. An appropriate initial IV levothyroxine loading dose in myxedema coma for adults is often in the range of:

  • 5–10 mcg
  • 50–100 mcg
  • 200–500 mcg
  • 1000–2000 mcg

Correct Answer: 200–500 mcg

Q25. Levothyroxine therapy can interact with warfarin by:

  • Decreasing warfarin anticoagulant effect via increased vitamin K synthesis
  • Increasing warfarin effect and INR by accelerating clotting factor catabolism
  • Directly binding warfarin in the gut and reducing its absorption
  • No clinically significant interaction exists

Correct Answer: Increasing warfarin effect and INR by accelerating clotting factor catabolism

Q26. Common pharmaceutical formulations available for levothyroxine include:

  • Tablets, oral solution, and intravenous injection
  • Only chewable tablets
  • Only topical cream
  • Only transdermal patches

Correct Answer: Tablets, oral solution, and intravenous injection

Q27. In differentiated thyroid cancer, levothyroxine is used therapeutically to:

  • Stimulate TSH to promote tumor growth
  • Suppress TSH to reduce risk of recurrence
  • Replace iodine in thyroid tissue
  • Act as chemotherapy to kill thyroid cells

Correct Answer: Suppress TSH to reduce risk of recurrence

Q28. Clinical features suggesting inadequate levothyroxine replacement include:

  • Insomnia, tremor, increased appetite
  • Fatigue, cold intolerance, weight gain
  • Palpitations, diarrhea, heat intolerance
  • Flushing, hyperhidrosis, tachycardia

Correct Answer: Fatigue, cold intolerance, weight gain

Q29. Chronic overreplacement with levothyroxine can increase the risk of which long‑term complication?

  • Osteoporosis
  • Chronic renal failure
  • Peripheral neuropathy
  • Hepatitis

Correct Answer: Osteoporosis

Q30. After a stable change in levothyroxine dose, the recommended interval before repeating TSH measurement is:

  • 48 hours
  • 1 week
  • 6–8 weeks
  • 6 months

Correct Answer: 6–8 weeks

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