Introduction: Posology is the science of dosing — defining the appropriate drug dose, frequency, and duration based on drug properties and patient characteristics. This section covers the definition of posology and key factors affecting posology, including pharmacokinetics (absorption, distribution, metabolism, excretion), pharmacodynamics, age, weight, renal and hepatic function, drug interactions, therapeutic index, and genetic variability. Understanding these concepts helps B.Pharm students design safe dosing regimens, anticipate adverse effects, and individualize therapy. Emphasis on calculation methods, dose adjustment strategies, and clinical considerations will deepen practical competence. These MCQs include scenario-based and calculation questions to prepare you for exams and pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the best definition of posology?
- The science of drug formulation and manufacturing
- The study of dose, frequency, and duration of drug therapy
- The study of adverse drug reactions
- The study of drug marketing and distribution
Correct Answer: The study of dose, frequency, and duration of drug therapy
Q2. Which pharmacokinetic factor most directly affects maintenance dosing?
- Volume of distribution (Vd)
- Bioavailability (F)
- Clearance (CL)
- Absorption rate constant (Ka)
Correct Answer: Clearance (CL)
Q3. Which components are required to calculate a loading dose?
- Clearance and dosing interval
- Desired plasma concentration, volume of distribution, and bioavailability
- Half-life and absorption rate
- Therapeutic index and protein binding
Correct Answer: Desired plasma concentration, volume of distribution, and bioavailability
Q4. The maintenance infusion rate (steady-state dosing rate) is best described by which expression?
- Vd × desired plasma concentration
- CL × desired plasma concentration / F
- 0.693 × Vd / CL
- F × dosing interval / CL
Correct Answer: CL × desired plasma concentration / F
Q5. Which formula correctly expresses elimination half-life (t1/2)?
- t1/2 = (0.693 × Vd) / CL
- t1/2 = CL / Vd
- t1/2 = Vd × CL
- t1/2 = F × dose / Vd
Correct Answer: t1/2 = (0.693 × Vd) / CL
Q6. Approximately how long does it take to reach steady state after starting a drug with first-order kinetics?
- One half-life
- Two half-lives
- Four to five half-lives
- Ten half-lives
Correct Answer: Four to five half-lives
Q7. Bioavailability (F) is defined as:
- The fraction of a drug dose that is excreted unchanged in urine
- The fraction of an administered dose that reaches systemic circulation as intact drug
- The fraction of drug bound to plasma proteins
- The fraction of drug metabolized in the liver
Correct Answer: The fraction of an administered dose that reaches systemic circulation as intact drug
Q8. A large volume of distribution (Vd) suggests which of the following?
- The drug is largely confined to plasma
- The drug is extensively distributed into tissues
- The drug has poor oral bioavailability
- The drug is highly renally excreted
Correct Answer: The drug is extensively distributed into tissues
Q9. The therapeutic index is best described as:
- The range between minimum effective concentration and toxic concentration
- The ratio of toxic dose to effective dose (e.g., TD50/ED50)
- The absolute plasma concentration of drug at steady state
- The fold increase in plasma concentration after a loading dose
Correct Answer: The ratio of toxic dose to effective dose (e.g., TD50/ED50)
Q10. High plasma protein binding of a drug primarily affects which parameter?
- Total plasma concentration but not free concentration
- Renal clearance directly
- Bioavailability after IV dosing
- Intrinsic absorption from the gut
Correct Answer: Total plasma concentration but not free concentration
Q11. The ‘first-pass effect’ primarily reduces which parameter for oral drugs?
- Volume of distribution
- Bioavailability
- Protein binding
- Elimination half-life for IV drugs
Correct Answer: Bioavailability
Q12. Which renal function estimate is most commonly used to adjust drug dosing in clinical practice?
- Serum urea concentration
- Measured GFR by inulin clearance
- Creatinine clearance estimated by Cockcroft-Gault
- Urine output over 24 hours
Correct Answer: Creatinine clearance estimated by Cockcroft-Gault
Q13. For pediatric dosing, which approach is commonly used for many drugs?
- Use the same adult dose for all children
- Dose based on body weight (mg/kg) or body surface area
- Dose only by age regardless of weight
- Dose inversely proportional to Vd
Correct Answer: Dose based on body weight (mg/kg) or body surface area
Q14. Which class of drugs most often requires therapeutic drug monitoring (TDM) due to narrow therapeutic index?
- Antacids
- Antiepileptics and aminoglycosides
- Topical corticosteroids
- Antihistamines
Correct Answer: Antiepileptics and aminoglycosides
Q15. In obesity, which body weight is often used for dosing highly lipophilic drugs?
- Ideal body weight (IBW)
- Actual body weight without adjustment
- Adjusted body weight
- Lean body weight only
Correct Answer: Adjusted body weight
Q16. Hepatic impairment most commonly necessitates which posology change?
- Increase the oral dose to overcome reduced absorption
- Reduce dose or extend dosing interval due to decreased metabolism
- Switch all drugs to IV administration
- No change because liver does not affect dosing
Correct Answer: Reduce dose or extend dosing interval due to decreased metabolism
Q17. Which pharmacokinetic parameter primarily determines the magnitude of a loading dose?
- Clearance (CL)
- Volume of distribution (Vd)
- Therapeutic index
- Protein binding
Correct Answer: Volume of distribution (Vd)
Q18. Which pharmacokinetic factor primarily determines the maintenance dose required to maintain steady-state concentration?
- Volume of distribution
- Clearance
- Absorption lag time
- Protein binding
Correct Answer: Clearance
Q19. A potent enzyme inducer co-administered with Drug X that is metabolized by CYP3A4 will most likely cause:
- Increased plasma concentration of Drug X
- No change in Drug X levels
- Decreased plasma concentration of Drug X
- Immediate toxicity of Drug X
Correct Answer: Decreased plasma concentration of Drug X
Q20. If a drug has a very long elimination half-life, how is dosing frequency usually affected?
- Requires more frequent dosing (e.g., hourly)
- Requires continuous IV infusion only
- Allows less frequent dosing (longer dosing intervals)
- Half-life does not influence dosing frequency
Correct Answer: Allows less frequent dosing (longer dosing intervals)
Q21. For an intravenous bolus administration, the bioavailability (F) of the drug is:
- Less than 100% due to first-pass metabolism
- Equal to 1 (100%)
- Dependent on protein binding
- Always zero
Correct Answer: Equal to 1 (100%)
Q22. The maintenance oral dose per dosing interval (Doseτ) can be calculated using which formula?
- Doseτ = (Vd × Css) / F
- Doseτ = (CL × Css × τ) / F
- Doseτ = 0.693 × Vd / CL
- Doseτ = F / (CL × τ)
Correct Answer: Doseτ = (CL × Css × τ) / F
Q23. When is a loading dose particularly useful?
- For drugs with very short half-lives when time to steady state is short
- For drugs with long half-lives when rapid attainment of target concentration is required
- When the therapeutic index is extremely wide and monitoring is unnecessary
- Only for topical medications
Correct Answer: For drugs with long half-lives when rapid attainment of target concentration is required
Q24. Which of the following is least likely to affect posology?
- Renal function
- Age and body weight
- Therapeutic index
- Tablet color
Correct Answer: Tablet color
Q25. Steady-state plasma concentration (Css) for continuous infusion depends primarily on:
- Infusion rate divided by clearance
- Volume of distribution only
- Absorption rate constant only
- Protein binding exclusively
Correct Answer: Infusion rate divided by clearance
Q26. Drug accumulation during repeated dosing is most directly related to which pair of factors?
- Therapeutic index and protein binding
- Half-life and dosing interval
- Bioavailability and tablet size
- Vd and tablet color
Correct Answer: Half-life and dosing interval
Q27. Which statement correctly contrasts therapeutic window and therapeutic index?
- Therapeutic index is the clinical concentration range; therapeutic window is TD50/ED50
- Therapeutic window is the clinical concentration range; therapeutic index is TD50/ED50
- Both terms are synonyms and interchangeable
- Neither relates to dosing or safety
Correct Answer: Therapeutic window is the clinical concentration range; therapeutic index is TD50/ED50
Q28. Which physiological changes in the elderly commonly require posology adjustments?
- Increased hepatic metabolism and faster clearance
- Improved renal function and higher Vd
- Reduced renal function and altered body composition
- No physiological changes relevant to drug dosing
Correct Answer: Reduced renal function and altered body composition
Q29. In the Cockcroft-Gault equation, which adjustment is applied for female patients?
- Multiply the result by 1.2
- Multiply the result by 0.85
- Subtract 10 mL/min from the result
- No adjustment is applied based on sex
Correct Answer: Multiply the result by 0.85
Q30. A drug has Vd = 40 L, desired plasma concentration = 5 mg/L, and oral bioavailability F = 0.50. What loading dose will achieve the target concentration?
- 100 mg
- 200 mg
- 400 mg
- 800 mg
Correct Answer: 400 mg
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