PEBC Pharmacology Basics 3 — Questions and Answers
Question 1: Which route of drug administration completely bypasses first-pass hepatic metabolism?
- Oral
- Rectal (proximal)
- Sublingual (Correct answer)
- Enteral via nasogastric tube
Correct answer: Sublingual
Sublingual administration allows drug absorption directly into systemic circulation via the sublingual veins, completely bypassing first-pass hepatic metabolism.
Question 2: The volume of distribution (Vd) of a highly lipophilic drug is expected to be:
- Low, confined to plasma
- Similar to plasma volume (~3 L)
- Very large, distributed into fat tissues (Correct answer)
- Equal to total body water (~42 L)
Correct answer: Very large, distributed into fat tissues
Highly lipophilic drugs partition extensively into fatty tissues, resulting in a very large apparent volume of distribution.
Question 3: An irreversible antagonist differs from a competitive antagonist in that it:
- Can be overcome by increasing agonist concentration
- Causes a parallel rightward shift of the dose-response curve
- Decreases the maximum response (Emax) that can be achieved (Correct answer)
- Has higher affinity for the receptor
Correct answer: Decreases the maximum response (Emax) that can be achieved
An irreversible antagonist covalently or very tightly binds to the receptor, permanently reducing available receptors and lowering the achievable Emax.
Question 4: CYP3A4 induction by rifampin would most likely result in:
- Increased plasma levels of co-administered CYP3A4 substrates
- Decreased metabolism of CYP3A4 substrates
- Reduced efficacy of drugs metabolized by CYP3A4 (Correct answer)
- Prolonged half-life of CYP3A4 substrates
Correct answer: Reduced efficacy of drugs metabolized by CYP3A4
Rifampin induces CYP3A4, accelerating the metabolism of co-administered CYP3A4 substrates and reducing their plasma concentrations and efficacy.
Question 5: Which pharmacodynamic concept describes the concentration at which a drug produces 50% of its maximum effect?
- LD50
- ED50
- EC50 (Correct answer)
- TD50
Correct answer: EC50
EC50 (half-maximal effective concentration) is the drug concentration that produces 50% of the maximum pharmacological effect and reflects receptor potency.
Question 6: Passive diffusion across a cell membrane is MOST dependent on which drug property?
- Molecular weight only
- Protein binding percentage
- Lipid solubility and degree of ionization (Correct answer)
- Water solubility
Correct answer: Lipid solubility and degree of ionization
Passive diffusion is governed primarily by a drug's lipid solubility and its un-ionized fraction, as only non-ionized, lipophilic forms cross membranes readily.
Question 7: Which statement about zero-order kinetics is correct?
- The rate of elimination is proportional to drug concentration
- A constant amount of drug is eliminated per unit time (Correct answer)
- The half-life remains constant regardless of dose
- It applies to most drugs at therapeutic concentrations
Correct answer: A constant amount of drug is eliminated per unit time
Zero-order kinetics describes elimination of a fixed amount of drug per unit time regardless of concentration, seen when metabolic enzymes are saturated (e.g., ethanol, phenytoin at high doses).
PEBC Pharmacology Basics 3
Which route of drug administration completely bypasses first-pass hepatic metabolism?