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,Pharmacokinetics & Pharmacodynamics
1. The process by which a drug moves from the site of administration into the bloodstream is
called:
• A) Distribution
• B) Metabolism
• C) Absorption
• D) Excretion
Correct Answer: C
Rationale: Absorption is the first step in pharmacokinetics, describing the movement of
a drug from its site of administration into the bloodstream. Distribution (A) is the
movement from blood to tissues, metabolism (B) is biotransformation, and excretion (D)
is elimination.
2. Bioavailability refers to:
• A) The percentage of drug that reaches the systemic circulation
• B) The amount of drug that is metabolized
• C) The rate at which the drug is excreted
• D) The volume of distribution of the drug
Correct Answer: A
Rationale: Bioavailability is the fraction of an administered dose that reaches systemic
circulation in an unchanged form. IV drugs have 100% bioavailability, while oral drugs
have variable bioavailability due to first-pass metabolism.
3. A 68-year-old male with hepatic cirrhosis is prescribed a medication that undergoes
extensive first-pass metabolism. Which pharmacokinetic change is MOST expected when
switching from oral to sublingual administration?
• A) Decreased bioavailability due to bypass of gut metabolism
, • B) Increased bioavailability due to bypass of hepatic first-pass metabolism
• C) No change in bioavailability because sublingual absorption is identical to oral
• D) Decreased onset of action due to delayed gastric emptying
Correct Answer: B
Rationale: Sublingual administration bypasses both intestinal and hepatic first-pass
metabolism, directly entering systemic circulation and increasing bioavailability. This is
clinically relevant in patients with cirrhosis or for drugs like nitroglycerin.
4. A patient taking warfarin (highly protein-bound, 99%) is started on
sulfamethoxazole/trimethoprim (also highly protein-bound). What pharmacokinetic
consequence is MOST likely?
• A) Warfarin metabolism increases, requiring dose escalation
• B) Free warfarin levels rise, increasing bleeding risk
• C) Warfarin absorption decreases, reducing anticoagulation
• D) No clinically significant interaction occurs
Correct Answer: B
Rationale: Both drugs compete for albumin binding sites; sulfamethoxazole displaces
warfarin, raising the free (active) fraction and INR. This is a classic protein-binding
displacement interaction.
5. A drug has a half-life of 12 hours. Approximately how long will it take to reach steady state
when administered at consistent dosing intervals?
• A) 12 hours (1 half-life)
• B) 24 hours (2 half-lives)
• C) 48 hours (4 half-lives)
• D) 60 hours (5 half-lives)
Correct Answer: D
, Rationale: Steady state is reached after approximately 4–5 half-lives. With a 12-hour
half-life, steady state is achieved in 48–60 hours.
6. A patient is a CYP2D6 poor metabolizer. Which medication requires dose reduction or
alternative selection due to reduced metabolism?
• A) Codeine (prodrug requiring activation)
• B) Phenytoin (CYP2C9 metabolized)
• C) Warfarin (CYP2C9 metabolized)
• D) Omeprazole (CYP2C19 metabolized)
Correct Answer: A
Rationale: Codeine is a prodrug that must be converted to morphine by CYP2D6. Poor
metabolizers cannot effectively activate it, reducing efficacy.
7. A patient is prescribed a weak acid medication with a pKa of 4.5. In which body
compartment will this drug primarily be absorbed?
• A) Stomach (pH 1.5–2.0)
• B) Small intestine (pH 6.0–7.5)
• C) Blood (pH 7.35–7.45)
• D) Urine (pH 5.0–8.0)
Correct Answer: A
Rationale: Weak acids are non-ionized and lipid-soluble in acidic environments. When
pH < pKa, the acidic drug is predominantly non-ionized, favoring absorption. Stomach pH
(1.5–2.0) is below the pKa of 4.5.
8. A patient is taking two drugs that are highly protein-bound (98% each). Which
pharmacokinetic phenomenon is most likely to occur?
• A) Decreased drug half-life
• B) Drug displacement and increased free drug concentration