Pharmacology - NAPLEX

1. What is the primary mechanism of action of amphotericin B?

   Binds ergosterol to form membrane pores causing cell leakage. Amphotericin B creates channels in fungal membranes, allowing leakage of cellular contents and leading to cell death.

2. What is the primary mechanism of action of spironolactone?

   Aldosterone receptor antagonist in collecting duct (potassium-sparing). Spironolactone blocks mineralocorticoid effects, reducing sodium reabsorption while preserving potassium in the distal nephron.

3. What is the primary mechanism of action of heparin?

   Potentiates antithrombin to inhibit thrombin (IIa) and factor Xa. Heparin enhances the activity of a natural anticoagulant, rapidly inactivating key clotting factors to prevent thrombus formation.

4. What is the primary mechanism of action of warfarin?

   Inhibits VKORC1, decreasing factors II, VII, IX, X and proteins C, S. Warfarin blocks vitamin K recycling, depleting gamma-carboxylated clotting factors necessary for blood coagulation.

5. What is the primary mechanism of action of clopidogrel?

   Irreversibly blocks P2Y12 (ADP) receptor to inhibit platelet aggregation. Clopidogrel prevents ADP-mediated activation of glycoprotein IIb/IIIa, crucial for platelet cross-linking and clot formation.

6. What is the primary mechanism of action of loop diuretics (for example, furosemide)?

   Inhibit Na-K-2Cl cotransporter in thick ascending limb. Loop diuretics cause potent natriuresis by inhibiting salt transport in the loop of Henle, decreasing extracellular fluid volume.

7. What is the primary mechanism of action of vancomycin?

   Binds $D$-Ala-$D$-Ala to inhibit peptidoglycan cell wall synthesis. Vancomycin targets the terminal dipeptide in peptidoglycan precursors, halting cell wall assembly in Gram-positive bacteria.

8. What is the primary mechanism of action of macrolides (for example, azithromycin)?

   Bind $50S$ ribosome to inhibit translocation and protein synthesis. Macrolides prevent the movement of the peptidyl-tRNA from the A site to the P site during translation elongation.

9. What is the primary mechanism of action of aminoglycosides?

   Irreversibly bind $30S$ ribosome causing misreading and bactericidal effect. Aminoglycosides disrupt protein synthesis by interfering with mRNA reading on the ribosome, resulting in faulty proteins and bacterial death.

10. What is the primary mechanism of action of statins (for example, atorvastatin)?

    Inhibit HMG-CoA reductase to decrease hepatic cholesterol synthesis. Statins lower LDL cholesterol by blocking the rate-limiting step in the mevalonate pathway, upregulating LDL receptors.

11. What is the primary mechanism of action of oseltamivir?

    Neuraminidase inhibitor that blocks influenza virion release. Oseltamivir prevents sialic acid cleavage, trapping new influenza viruses on the host cell surface and limiting spread.

12. What is the primary mechanism of action of sulfonylureas (for example, glipizide)?

    Close pancreatic KATP channels to increase insulin release. Sulfonylureas stimulate beta cells by blocking potassium efflux, depolarizing the membrane and triggering insulin secretion.

13. What is the antidote for heparin-induced bleeding?

    Protamine sulfate. Protamine neutralizes heparin's anticoagulant effect by forming a stable complex, restoring normal clotting.

14. What is the primary mechanism of action of metformin?

    Decreases hepatic gluconeogenesis and increases insulin sensitivity. Metformin improves glycemic control by suppressing liver glucose output and enhancing peripheral glucose uptake.

15. What is the reversal agent for warfarin in life-threatening bleeding?

    Four-factor PCC plus vitamin K (phytonadione). This combination rapidly replenishes vitamin K-dependent factors and supports long-term correction of coagulopathy.

16. What is the primary mechanism of action of azole antifungals (for example, fluconazole)?

    Inhibit $14$-$\alpha$-demethylase to reduce ergosterol synthesis. Azoles disrupt fungal membrane integrity by inhibiting a key enzyme in the ergosterol biosynthetic pathway.

17. What is the primary mechanism of action of thiazide diuretics (for example, HCTZ)?

    Inhibit NaCl cotransporter in distal convoluted tubule. Thiazides promote diuresis by blocking sodium reabsorption in the distal nephron, reducing blood volume and pressure.

18. What is the primary mechanism of action of naloxone?

    Competitive opioid receptor antagonist (highest affinity for $\mu$). Naloxone reverses opioid effects by competitively displacing agonists from receptors, particularly the mu subtype involved in analgesia and respiratory depression.

19. What is the primary mechanism of action of ARBs (for example, losartan)?

    Block angiotensin II type 1 (AT1) receptors. ARBs prevent angiotensin II from binding its receptor, mitigating vasoconstriction and aldosterone release without affecting bradykinin.

20. What is the primary mechanism of action of beta-lactam antibiotics?

    Inhibit PBPs (transpeptidases) to block bacterial cell wall cross-linking. Beta-lactams weaken bacterial cell walls by preventing the final cross-linking step in peptidoglycan synthesis, leading to cell lysis.

21. What is the primary mechanism of action of trimethoprim-sulfamethoxazole?

    Sequential folate synthesis inhibition (DHPS then DHFR). The combination synergistically blocks tetrahydrofolate production, essential for bacterial nucleotide synthesis and growth.

22. What is the primary mechanism of action of ACE inhibitors (for example, lisinopril)?

    Inhibit ACE, decreasing angiotensin II and increasing bradykinin. ACE inhibitors reduce vasoconstriction and sodium retention while potentiating a vasodilatory peptide, lowering blood pressure.

23. What is the primary mechanism of action of aspirin at antiplatelet doses?

    Irreversibly inhibits COX-1, decreasing thromboxane A2. Aspirin suppresses platelet activation by reducing a pro-aggregatory eicosanoid, providing antithrombotic effects.

24. What is the primary mechanism of action of acyclovir?

    Guanosine analog; inhibits viral DNA polymerase after phosphorylation. Acyclovir mimics a nucleoside and, once activated by viral thymidine kinase, terminates DNA chain elongation in herpes viruses.

25. What is the primary mechanism of action of fluoroquinolones (for example, levofloxacin)?

    Inhibit DNA gyrase (topoisomerase II) and topoisomerase IV. Fluoroquinolones interfere with bacterial DNA replication and repair by targeting enzymes essential for supercoiling and decatenation.

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