NAPLEX QBANK Pharmacology and Mechanism of Action Questions and Answers 1 — Questions and Answers
Question 1: A patient is being treated for gout with allopurinol. Which of the following best describes the mechanism of action responsible for its therapeutic effect?
- Increasing the renal excretion of uric acid
- Inhibiting the reabsorption of uric acid in the proximal tubule
- Inhibiting xanthine oxidase, which reduces the production of uric acid (Correct answer)
- Binding to uric acid crystals to promote their dissolution
Correct answer: Inhibiting xanthine oxidase, which reduces the production of uric acid
Allopurinol and its active metabolite, oxypurinol, lower uric acid levels by inhibiting xanthine oxidase. This enzyme is responsible for the conversion of hypoxanthine to xanthine and then to uric acid, the final step in purine metabolism.
Question 2: A patient with gastroesophageal reflux disease (GERD) is prescribed omeprazole. This drug provides symptom relief primarily by which of the following mechanisms?
- Neutralizing existing stomach acid
- Blocking histamine H2-receptors on parietal cells
- Forming a protective barrier over the gastric mucosa
- Irreversibly inhibiting the H+/K+ ATPase pump in parietal cells (Correct answer)
Correct answer: Irreversibly inhibiting the H+/K+ ATPase pump in parietal cells
Omeprazole is a proton pump inhibitor (PPI) that specifically and irreversibly blocks the H+/K+ ATPase enzyme system (the 'proton pump') on the secretory surface of gastric parietal cells. This action inhibits the final step in gastric acid production.
Question 3: A patient on long-term anticoagulation with warfarin for atrial fibrillation needs to understand how the medication works. Which statement accurately describes warfarin's mechanism of action?
- It directly inhibits thrombin (Factor IIa)
- It prevents platelet aggregation by blocking ADP receptors
- It inhibits the activation of vitamin K-dependent clotting factors (Correct answer)
- It potentiates the activity of antithrombin III
Correct answer: It inhibits the activation of vitamin K-dependent clotting factors
Warfarin inhibits the enzyme vitamin K epoxide reductase complex 1 (VKORC1). This action interferes with the activation of vitamin K, which is a necessary cofactor for the synthesis of clotting factors II, VII, IX, and X in the liver.
Question 4: A patient is prescribed clopidogrel after having a coronary artery stent placed. Which of the following is the primary mechanism by which clopidogrel exerts its antiplatelet effect?
- Irreversible inhibition of the P2Y12 ADP receptor on platelets (Correct answer)
- Inhibition of the cyclooxygenase-1 (COX-1) enzyme
- Blockade of the glycoprotein IIb/IIIa receptor
- Reversible antagonism of the protease-activated receptor-1 (PAR-1)
Correct answer: Irreversible inhibition of the P2Y12 ADP receptor on platelets
Clopidogrel is a prodrug whose active metabolite irreversibly binds to the P2Y12 class of ADP receptors on the platelet surface. This binding prevents ADP from activating the platelets, thereby inhibiting platelet aggregation for the life of the platelet.
Question 5: A patient is brought to the emergency department with respiratory depression following a suspected heroin overdose. The administration of naloxone rapidly improves the patient's breathing. What is the mechanism of action of naloxone?
- It stimulates the respiratory center in the medulla
- It is a competitive antagonist at opioid receptors (Correct answer)
- It metabolizes opioids into inactive compounds
- It acts as a partial agonist at the mu-opioid receptor
Correct answer: It is a competitive antagonist at opioid receptors
Naloxone is a competitive opioid receptor antagonist. It has a high affinity for opioid receptors, particularly the mu-receptor, and displaces opioids that are already bound, thereby reversing their effects, including respiratory depression.
Question 6: A child experiencing an acute asthma exacerbation is administered albuterol via a nebulizer. The therapeutic effect of this medication is achieved through which mechanism?
- Antagonism of muscarinic receptors leading to bronchodilation
- Inhibition of leukotriene synthesis
- Stabilization of mast cell membranes
- Stimulation of beta-2 adrenergic receptors causing smooth muscle relaxation (Correct answer)
Correct answer: Stimulation of beta-2 adrenergic receptors causing smooth muscle relaxation
Albuterol is a selective beta-2 adrenergic receptor agonist. Stimulation of these receptors in the lungs leads to the relaxation of bronchial smooth muscle, resulting in bronchodilation and relief of bronchospasm.
NAPLEX QBANK Pharmacology and Mechanism of Action Questions and Answers 1
A patient is being treated for gout with allopurinol.
Which of the following best describes the mechanism of action responsible for its therapeutic effect?