Carbonic anhydrase inhibitors – Acetazolamide MCQs With Answer

Introduction: Carbonic anhydrase inhibitors (CAIs) are an important class in pharmacology, with acetazolamide being a key drug studied by B.Pharm students. This topic covers acetazolamide’s mechanism of action (zinc-binding inhibition of carbonic anhydrase), pharmacokinetics, proximal tubule diuretic effects, clinical uses (glaucoma, altitude sickness, metabolic alkalosis), adverse effects (metabolic acidosis, paresthesias, renal stones), contraindications (sulfonamide allergy, hepatic disease) and monitoring (electrolytes, bicarbonate). Understanding acetazolamide’s structure–activity, drug interactions and therapeutic limitations prepares students for rational drug use and exams. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary molecular mechanism by which acetazolamide inhibits carbonic anhydrase?

• Binding to the active-site zinc atom of the enzyme
• Covalent modification of serine residues
• Allosteric modulation at the enzyme surface
• Competitive inhibition with bicarbonate as substrate

Correct Answer: Binding to the active-site zinc atom of the enzyme

Q2. In which segment of the nephron does acetazolamide produce its major diuretic effect?

• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule
• Collecting duct

Correct Answer: Proximal convoluted tubule

Q3. Which clinical indication is acetazolamide commonly used for?

• Open-angle glaucoma
• Congestive heart failure as first-line therapy
• Severe hyperkalemia management
• Treatment of hypovolemic shock

Correct Answer: Open-angle glaucoma

Q4. Acetazolamide is widely used prophylactically for which condition?

• Prevention and treatment of acute mountain sickness
• Prevention of myocardial infarction
• Prophylaxis of deep vein thrombosis
• Prevention of diabetic ketoacidosis

Correct Answer: Prevention and treatment of acute mountain sickness

Q5. What is the characteristic acid–base change produced by acetazolamide?

• Metabolic acidosis (bicarbonate depletion)
• Metabolic alkalosis (bicarbonate retention)
• Respiratory acidosis
• Respiratory alkalosis

Correct Answer: Metabolic acidosis (bicarbonate depletion)

Q6. Which common adverse effect is associated with acetazolamide therapy?

• Paresthesias and tingling of the extremities
• Severe hyperglycemia
• Profound bradycardia
• Ototoxic deafness

Correct Answer: Paresthesias and tingling of the extremities

Q7. Acetazolamide should be avoided in patients with which hypersensitivity?

• Sulfonamide hypersensitivity
• Penicillin allergy
• NSAID sensitivity
• Opioid allergy

Correct Answer: Sulfonamide hypersensitivity

Q8. Which drug combination increases the risk of hypokalemia when given with acetazolamide?

• Loop diuretics (e.g., furosemide)
• Potassium-sparing diuretics (e.g., spironolactone)
• ACE inhibitors (e.g., lisinopril)
• Beta blockers (e.g., metoprolol)

Correct Answer: Loop diuretics (e.g., furosemide)

Q9. Carbonic anhydrase isoenzymes highly expressed in which tissues explain acetazolamide’s effects?

• Proximal tubule, red blood cells and choroid plexus
• Pancreas and skeletal muscle only
• Adipose tissue and lymph nodes
• Cardiac myocytes exclusively

Correct Answer: Proximal tubule, red blood cells and choroid plexus

Q10. What is the effect of acetazolamide on urine pH?

• Raises urine pH (alkalinization)
• Decreases urine pH (acidification)
• No significant change in urine pH
• Produces alternating acidification and alkalinization

Correct Answer: Raises urine pH (alkalinization)

Q11. How does acetazolamide reduce intracranial pressure?

• Decreases CSF production by choroid plexus carbonic anhydrase inhibition
• Increases CSF absorption at arachnoid granulations
• Blocks cerebral blood flow directly
• Acts as an osmotic diuretic to draw fluid from brain tissue

Correct Answer: Decreases CSF production by choroid plexus carbonic anhydrase inhibition

Q12. Which neurologic condition may acetazolamide be used as adjunct therapy?

• Certain forms of epilepsy (e.g., absence seizures)
• Acute ischemic stroke as initial therapy
• Parkinson’s disease as primary treatment
• Alzheimer’s disease to improve cognition

Correct Answer: Certain forms of epilepsy (e.g., absence seizures)

Q13. Severe overdose of acetazolamide primarily leads to which complication?

• Severe metabolic acidosis and electrolyte disturbances
• Acute hyperglycemia and ketoacidosis
• Profound hypertension and hypertensive crisis
• Life-threatening hemolysis

Correct Answer: Severe metabolic acidosis and electrolyte disturbances

Q14. Long-term use of acetazolamide predisposes to formation of which type of kidney stone?

• Calcium phosphate stones
• Uric acid stones
• Cystine stones
• Struvite (ammonium magnesium phosphate) stones

Correct Answer: Calcium phosphate stones

Q15. What is the recommendation regarding acetazolamide use in pregnancy?

• Avoid use in pregnancy due to potential teratogenicity
• Safe in all trimesters without restrictions
• Indicated as first-line treatment for hypertension in pregnancy
• Only topical use is contraindicated

Correct Answer: Avoid use in pregnancy due to potential teratogenicity

Q16. How is the inhibition of carbonic anhydrase by acetazolamide best described?

• Reversible inhibition of the enzyme active site
• Irreversible covalent inactivation
• Uncompetitive inhibition requiring substrate binding
• Only indirect inhibition via second messengers

Correct Answer: Reversible inhibition of the enzyme active site

Q17. Which metal ion in carbonic anhydrase’s active site is essential for acetazolamide binding?

• Zinc (Zn2+)
• Iron (Fe2+)
• Magnesium (Mg2+)
• Calcium (Ca2+)

Correct Answer: Zinc (Zn2+)

Q18. Why is acetazolamide less effective than loop or thiazide diuretics for chronic edema?

• Bicarbonate depletion and metabolic acidosis reduce its long-term diuretic efficacy
• It causes severe volume overload long-term
• It selectively increases sodium reabsorption in the loop
• It is not orally bioavailable for chronic use

Correct Answer: Bicarbonate depletion and metabolic acidosis reduce its long-term diuretic efficacy

Q19. A commonly recommended prophylactic dose of acetazolamide for altitude sickness is:

• 125 mg twice daily
• 5 mg once daily
• 2 g twice daily
• 50 mg once at bedtime

Correct Answer: 125 mg twice daily

Q20. What effect does acetazolamide have on serum bicarbonate concentration?

• Decreases serum bicarbonate
• Increases serum bicarbonate
• No change in serum bicarbonate
• Causes fluctuating bicarbonate without net change

Correct Answer: Decreases serum bicarbonate

Q21. Regarding cross-reactivity, acetazolamide as a sulfonamide derivative may:

• Pose a risk of cross-sensitivity in patients allergic to sulfonamide antibiotics
• Have zero risk of sulfonamide cross-reaction
• Only cross-react with penicillins
• Cause immediate anaphylaxis in all sulfonamide-allergic patients

Correct Answer: Pose a risk of cross-sensitivity in patients allergic to sulfonamide antibiotics

Q22. How does acetazolamide reduce aqueous humor formation in the eye?

• By inhibiting carbonic anhydrase in the ciliary epithelium, reducing bicarbonate and fluid secretion
• By increasing trabecular meshwork outflow resistance
• By blocking adrenergic receptors in the iris
• By acting as an osmotic agent in the lens

Correct Answer: By inhibiting carbonic anhydrase in the ciliary epithelium, reducing bicarbonate and fluid secretion

Q23. Which of the following is a topical carbonic anhydrase inhibitor used in glaucoma?

• Dorzolamide
• Furosemide
• Spironolactone
• Mannitol

Correct Answer: Dorzolamide

Q24. Acetazolamide is relatively contraindicated in which hepatic condition due to risk of encephalopathy?

• Hepatic cirrhosis with risk of hepatic encephalopathy
• Acute viral hepatitis without encephalopathy
• Nonalcoholic fatty liver disease without synthetic dysfunction
• Mild transaminase elevation only

Correct Answer: Hepatic cirrhosis with risk of hepatic encephalopathy

Q25. Which statement about acetazolamide and breastfeeding is correct?

• Acetazolamide is excreted in breast milk and requires caution during lactation
• Acetazolamide is not excreted in breast milk and is completely safe
• Acetazolamide enhances milk production and is recommended
• Breastfeeding prevents acetazolamide absorption in the infant

Correct Answer: Acetazolamide is excreted in breast milk and requires caution during lactation

Q26. Chemically, acetazolamide belongs to which class?

• Sulfonamide derivative
• Loop diuretic class
• Potassium-sparing diuretic class
• Osmotic diuretic class

Correct Answer: Sulfonamide derivative

Q27. How is acetazolamide primarily eliminated from the body?

• Renal excretion (unchanged drug) via the proximal tubule
• Extensive hepatic metabolism and biliary excretion
• Exhalation through the lungs
• Conjugation and fecal elimination mainly

Correct Answer: Renal excretion (unchanged drug) via the proximal tubule

Q28. In which acid–base disturbance can acetazolamide be therapeutically helpful?

• Metabolic alkalosis
• Respiratory acidosis
• Diabetic ketoacidosis as sole therapy
• Severe lactic acidosis

Correct Answer: Metabolic alkalosis

Q29. Why does the diuretic effect of acetazolamide decline with continued use?

• Bicarbonate depletion and enhanced distal nephron sodium reabsorption reduce diuresis
• It accumulates in the body causing receptor downregulation
• The drug is converted to an inactive form in the loop of Henle
• It permanently damages proximal tubule cells

Correct Answer: Bicarbonate depletion and enhanced distal nephron sodium reabsorption reduce diuresis

Q30. Which laboratory parameters should be routinely monitored in patients on acetazolamide?

• Serum electrolytes (especially potassium) and bicarbonate
• Only liver function tests
• Serum amylase and lipase exclusively
• Coagulation profile only

Correct Answer: Serum electrolytes (especially potassium) and bicarbonate

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