COMPREHENSIVE BASIC PHARMACOLOGY - 120 CHALLENGING MCQs

Question 1

Bioavailability is BEST defined as:

Accepted Answer

Fraction of unchanged drug reaching systemic circulation — Bioavailability (F) is the percentage of administered drug that reaches systemic circulation unchanged. IV route has 100% bioavailability by definition. ---

Question 2

A drug that undergoes extensive first-pass metabolism will show:

Accepted Answer

Reduced oral bioavailability — First-pass metabolism in the liver reduces the amount of drug reaching systemic circulation, decreasing oral bioavailability. Examples include nitroglycerin and propranolol. ---

Question 3

A patient with hepatic cirrhosis requires a drug with high first-pass metabolism. Which pharmacokinetic parameter change would you most expect?

Accepted Answer

Increased bioavailability — Hepatic cirrhosis reduces first-pass metabolism, so less drug is metabolized before reaching systemic circulation, resulting in increased bioavailability and risk of toxicity. ---

Question 4

Volume of distribution (Vd) increases when a drug is:

Accepted Answer

Highly lipid soluble — Lipid-soluble drugs penetrate cell membranes easily and distribute widely into tissues, resulting in large Vd values. ---

Question 5

A drug has a volume of distribution (Vd) of 400L in a 70kg patient. What does this indicate?

Accepted Answer

Drug is highly tissue-bound — A Vd of 400L (much larger than total body water ~42L) indicates the drug is extensively distributed and bound to tissues outside the vascular compartment. ---

Question 6

Clearance is defined as:

Accepted Answer

Volume of plasma cleared of drug per unit time — Clearance (CL) represents the volume of plasma from which drug is completely removed per unit time (mL/min or L/hr), reflecting elimination efficiency. ---

Question 7

The major determinant of half-life (t½) is:

Accepted Answer

Clearance and Vd — Half-life = (0.693 × Vd) / CL. It depends on both volume of distribution and clearance. Changes in either parameter affect t½. ---

Question 8

If a drug's half-life is 6 hours, approximately how long will it take to reach 97% steady-state concentration with continuous dosing?

Accepted Answer

30 hours — Steady state is reached after approximately 5 half-lives (5 × 6 = 30 hours), which achieves about 97% of the final steady-state concentration. ---

Question 9

Zero-order kinetics means:

Accepted Answer

A constant amount is eliminated — In zero-order kinetics, a fixed amount (not fraction) of drug is eliminated per unit time, regardless of concentration. Occurs with enzyme saturation (e.g., high-dose aspirin, alcohol, phenytoin). ---

Question 10

Which statement about zero-order kinetics is TRUE?

Accepted Answer

Elimination rate is independent of drug concentration — In zero-order kinetics, a constant AMOUNT (not fraction) is eliminated per unit time, regardless of concentration. This occurs when elimination mechanisms are saturated. ---

Question 11

Steady-state concentration in continuous infusion mainly depends on:

Accepted Answer

Clearance — Steady-state concentration (Css) = Infusion rate / Clearance. It's determined by the balance between input rate and elimination (clearance), not by Vd or t½. ---

Question 12

A loading dose is required to:

Accepted Answer

Rapidly achieve therapeutic concentration — Loading doses rapidly achieve therapeutic concentrations without waiting 5 half-lives. Loading dose = (Vd × Target concentration) / Bioavailability. ---

Question 13

A drug is 95% protein-bound. In a patient with hypoalbuminemia, what is the most likely consequence?

Accepted Answer

Decreased total drug concentration, unchanged free drug concentration — With less protein available for binding, total drug decreases, but the body maintains free (active) drug concentration through homeostatic mechanisms and increased clearance. ---

Question 14

Which organ is MOST responsible for Phase I metabolism?

Accepted Answer

Liver — The liver contains the highest concentration of CYP450 enzymes responsible for Phase I reactions (oxidation, reduction, hydrolysis). ---

Question 15

Phase II reactions mainly involve:

Accepted Answer

Conjugation — Phase II metabolism involves conjugation reactions (glucuronidation, sulfation, acetylation, methylation) that increase water solubility for excretion. ---

Question 16

A drug undergoes phase II metabolism. What does this typically involve?

Accepted Answer

Conjugation reactions — Phase II metabolism involves conjugation reactions (glucuronidation, sulfation, acetylation) that make drugs more water-soluble for excretion. Phase I involves oxidation, reduction, and hydrolysis. ---

Question 17

Oral absorption is most affected by:

Accepted Answer

Intestinal motility — affects contact time with absorptive surfaces. Increased motility (diarrhea) reduces absorption; decreased motility increases it. ---

Question 18

A lipophilic drug with pKa of 8.4 is administered orally. In which environment will it be most absorbed?

Accepted Answer

Ileum (pH 8) — For a weak base (pKa 8.4), the drug is more unionized in less acidic environments. At pH 8, closer to its pKa, more drug is in the lipophilic unionized form, favoring absorption. ---

Question 19

Drugs excreted unchanged by kidney tend to be:

Accepted Answer

Highly water soluble — Water-soluble (polar) drugs cannot be reabsorbed from renal tubules and are excreted unchanged. Lipid-soluble drugs are reabsorbed or metabolized first. ---

Question 20

Enterohepatic circulation tends to:

Accepted Answer

Prolong half-life — Enterohepatic circulation (drug excreted in bile, reabsorbed in intestine, returned to liver) recycles drug, prolonging presence in the body and increasing half-life. ---

Question 21

Which increases the half-life of a renally cleared drug?

Accepted Answer

Reduced GFR — Reduced glomerular filtration rate (GFR) decreases renal clearance, increasing half-life. This is critical in elderly patients and those with renal disease. ---

Question 22

A drug with high first-pass effect is best avoided via:

Accepted Answer

Oral route — Oral drugs undergo first-pass metabolism in the liver. Alternative routes (sublingual, IV, IM, transdermal) bypass or reduce first-pass effect. ---

Question 23

Two drugs are co-administered. Drug A inhibits CYP3A4, and Drug B is a CYP3A4 substrate. What is the expected outcome?

Accepted Answer

Increased plasma levels of Drug B — Inhibiting CYP3A4 decreases the metabolism of Drug B, leading to increased plasma levels and potential toxicity. Common with grapefruit juice, ketoconazole, erythromycin. ---

Question 24

Which factor would LEAST affect the rate of drug absorption from an intramuscular injection site?

Accepted Answer

First-pass metabolism — occurs when drugs pass through the liver after oral absorption. IM injections bypass the GI tract and enter systemic circulation directly, avoiding first-pass metabolism. ---

Question 25

A drug has a clearance of 120 mL/min and a volume of distribution of 50L. What is its half-life?

Accepted Answer

4.8 hours — Half-life = (0.693 × Vd) / CL = (0.693 × 50,000 mL) / 120 mL/min = 289 minutes ≈ 4.8 hours. --- ## SECTION B: PHARMACODYNAMICS (25 Questions) ---

Question 26

Efficacy refers to:

Accepted Answer

Ability to produce maximal response — Efficacy (Emax) is the maximal effect a drug can produce, regardless of dose. It's related to intrinsic activity and differs from potency. ---

Question 27

Potency refers to:

Accepted Answer

Amount of drug required to produce effect — Potency is the dose or concentration required to produce a specific effect (usually EC50). A more potent drug requires less dose to achieve the same effect. ---

Question 28

Which statement best describes potency?

Accepted Answer

The dose required to produce 50% of maximal effect — Potency refers to the concentration or dose required to produce a specific effect (typically EC50 or ED50). A more potent drug requires less dose to achieve the same effect. ---

Question 29

A competitive antagonist shifts the dose-response curve:

Accepted Answer

Rightward, same maximal effect — Competitive antagonists bind reversibly to the same site as the agonist, requiring more agonist to achieve the same effect (rightward shift), but maximal effect remains achievable. ---

Question 30

Which type of antagonism can be overcome by increasing the agonist concentration?

Accepted Answer

Competitive antagonism — is reversible and surmountable. Increasing agonist concentration can outcompete the antagonist for receptor binding, restoring the maximal effect. ---

Question 31

An irreversible antagonist:

Accepted Answer

Reduces efficacy — Irreversible antagonists bind covalently or very tightly, permanently reducing the number of available receptors, thereby reducing maximal response (efficacy) that cannot be overcome. ---

Question 32

A noncompetitive antagonist causes:

Accepted Answer

Decreased maximal response — Non-competitive antagonists reduce the maximal effect (efficacy) by binding to allosteric sites or irreversibly, and this cannot be overcome by increasing agonist concentration. ---

Question 33

A partial agonist is administered to a patient already taking a full agonist at the same receptor. What effect would you expect?

Accepted Answer

Decreased effect compared to full agonist alone — A partial agonist has lower intrinsic activity than a full agonist. When both are present, the partial agonist competes for receptors but produces less effect, resulting in decreased overall response. ---

Question 34

A partial agonist:

Accepted Answer

Produces lower maximal effect than full agonist — Partial agonists bind to receptors but have lower intrinsic activity, producing submaximal responses even at full receptor occupancy. Can act as antagonists in presence of full agonists. ---

Question 35

An inverse agonist differs from an antagonist because it:

Accepted Answer

Produces an effect opposite to the agonist by reducing constitutive receptor activity — Inverse agonists bind to receptors and reduce constitutive (baseline) activity below normal levels, whereas competitive antagonists simply block agonist binding without affecting basal activity. ---

Question 36

Therapeutic index (TI) indicates:

Accepted Answer

Margin of safety — TI = TD50/ED50 or LD50/ED50. A higher TI indicates a wider margin between therapeutic and toxic doses, meaning greater safety. ---

Question 37

A drug has an ED50 of 10mg and a TD50 of 100mg. What is its therapeutic index?

Accepted Answer

0.1 — Therapeutic Index = TD50/ED50 = 100/10 = 10. A higher therapeutic index indicates a wider margin of safety between therapeutic and toxic doses. ---

Question 38

A drug with narrow TI requires:

Accepted Answer

Therapeutic drug monitoring — Drugs with narrow TI (small difference between therapeutic and toxic doses) require therapeutic drug monitoring to ensure safety and efficacy (e.g., warfarin, digoxin, phenytoin, lithium). ---

Question 39

Agonists activate receptors by binding to:

Accepted Answer

Orthosteric sites — are the primary binding sites where endogenous ligands bind. Agonists bind here to activate receptors. Allosteric sites are secondary binding sites. ---

Question 40

Tachyphylaxis is:

Accepted Answer

Rapidly decreasing response to drug — Tachyphylaxis is acute, rapid tolerance that develops quickly (minutes to hours) with repeated administration, such as with ephedrine, nitrates, or amphetamines. ---

Question 41

Tachyphylaxis is best described as:

Accepted Answer

Rapid decrease in drug response after repeated doses — Tachyphylaxis is acute, rapid tolerance that develops quickly (minutes to hours) with repeated administration, such as with ephedrine or nitrates. ---

Question 42

Desensitization of receptors occurs due to:

Accepted Answer

Prolonged stimulation — Prolonged receptor stimulation leads to desensitization through receptor phosphorylation, internalization, or uncoupling from signaling pathways (e.g., beta-receptor desensitization with chronic beta-agonist use). ---

Question 43

Desensitization of receptors typically involves:

Accepted Answer

Receptor phosphorylation and internalization — Acute desensitization often involves receptor phosphorylation (e.g., by G protein-coupled receptor kinases) followed by receptor internalization or uncoupling from signaling pathways. ---

Question 44

The median effective dose (ED50) is:

Accepted Answer

Dose that produces effect in half population — ED50 is the dose that produces the desired therapeutic effect in 50% of the population. It's a measure of drug potency. ---

Question 45

The median toxic dose (TD50) is:

Accepted Answer

Dose that produces toxicity in 50 percent — TD50 is the dose that produces a specified toxic effect in 50% of the population. Used to calculate therapeutic index: TI = TD50/ED50. ---

Question 46

Intrinsic activity refers to:

Accepted Answer

Ability to activate receptor — Intrinsic activity (efficacy) is the ability of a drug-receptor complex to produce a response. Full agonists have high intrinsic activity; antagonists have zero. ---

Question 47

A drug-receptor interaction shows a Kd of 10 nM. What does this indicate?

Accepted Answer

High affinity of the drug for the receptor — Kd (dissociation constant) represents the concentration at which 50% of receptors are occupied. A lower Kd (like 10 nM) indicates higher affinity (tighter binding). ---

Question 48

The concept of "spare receptors" means:

Accepted Answer

Maximal response can be achieved without occupying all receptors — Spare receptors exist when the system can produce a maximal response with less than 100% receptor occupancy, indicating high receptor reserve and amplification in the signaling cascade. ---

Question 49

A drug produces its effect through a G-protein coupled receptor. Which is the correct signaling sequence?

Accepted Answer

Receptor → G-protein → Effector enzyme → Second messenger — The correct GPCR cascade: Agonist binds receptor → Receptor activates G-protein → G-protein modulates effector enzyme (e.g., adenylyl cyclase) → Enzyme produces second messenger (e.g., cAMP). ---

Question 50

Idiosyncratic reactions are due to:

Accepted Answer

Genetic variations — Idiosyncratic reactions are unpredictable, unusual responses often due to genetic polymorphisms (e.g., G6PD deficiency causing hemolysis with certain drugs, or malignant hyperthermia). --- ## SECTION C: ROUTES OF ADMINISTRATION (18 Questions) ---

COMPREHENSIVE BASIC PHARMACOLOGY - 120 CHALLENGING MCQs

Questions, Answers & Explanations