Factors affecting posology MCQs With Answer

Introduction

Posology is the science of dose selection and dosage adjustment in pharmacy. For safe, individualized therapy, B. Pharm students must master factors affecting dose: age, body weight, body surface area (BSA), pharmacokinetics (absorption, distribution, metabolism, excretion), pharmacodynamics, renal impairment, hepatic dysfunction, pharmacogenetics, drug–drug and drug–food interactions, pregnancy and lactation, route of administration, bioavailability, plasma protein binding, and therapeutic index. Clinical tools like creatinine clearance (CrCl), estimated GFR, Child–Pugh score, half-life, and BSA-based calculations guide loading vs maintenance dosing, interval selection, and toxicity prevention—especially for narrow therapeutic index drugs. This overview builds the foundation for rational dose calculation, adjustment, and monitoring in diverse patient populations. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. For which type of medicines is dosing by body surface area (mg/m²) preferred to minimize toxicity risk?

• Cytotoxic anticancer agents
• Penicillins
• Antacids
• Antihistamines

Correct Answer: Cytotoxic anticancer agents

Q2. Which formula correctly estimates body surface area (BSA) by the Mosteller method?

• BSA = √([height in cm × weight in kg] / 3600)
• BSA = (height in cm × weight in kg) / 1000
• BSA = (height in m² + weight in kg) / 2
• BSA = √([height in m × weight in kg] / 100)

Correct Answer: BSA = √([height in cm × weight in kg] / 3600)

Q3. Which pediatric physiologic characteristic most increases the volume of distribution for water-soluble drugs?

• Higher total body water and extracellular fluid
• Lower gastric pH
• Higher albumin concentration
• Accelerated renal clearance

Correct Answer: Higher total body water and extracellular fluid

Q4. Why is chloramphenicol associated with “gray baby syndrome” in neonates?

• Underdeveloped glucuronidation (UGT) leads to impaired metabolism
• Rapid N-acetylation causes toxic metabolite formation
• Markedly increased CYP3A4 activity lowers drug exposure
• Excessive renal clearance rapidly eliminates the drug

Correct Answer: Underdeveloped glucuronidation (UGT) leads to impaired metabolism

Q5. Which parameter is most appropriate to guide dose adjustment of primarily renally cleared drugs?

• Creatinine clearance (CrCl) or estimated GFR
• Serum creatinine alone
• Blood urea nitrogen (BUN) alone
• Hemoglobin level

Correct Answer: Creatinine clearance (CrCl) or estimated GFR

Q6. Which equation is commonly used to estimate creatinine clearance for adult drug dosing?

• Cockcroft–Gault equation
• Child–Pugh score
• APGAR score
• CHA₂DS₂-VASc score

Correct Answer: Cockcroft–Gault equation

Q7. Which tool is routinely used to stage hepatic impairment and guide dose adjustment in cirrhosis?

• Child–Pugh classification
• APACHE II score
• Wells score
• Bishop score

Correct Answer: Child–Pugh classification

Q8. Which physiologic change in pregnancy most often necessitates a higher loading dose of hydrophilic drugs?

• Increased plasma volume and total body water
• Decreased glomerular filtration rate
• Decreased CYP3A4 activity
• Reduced cardiac output

Correct Answer: Increased plasma volume and total body water

Q9. Which enzyme activity decreases during pregnancy, potentially increasing caffeine exposure?

• CYP1A2 decreases during pregnancy
• CYP3A4 decreases during pregnancy
• UGT activity universally decreases
• All major CYP enzymes increase

Correct Answer: CYP1A2 decreases during pregnancy

Q10. Which statement best predicts low drug transfer into breast milk?

• High protein binding and large volume of distribution
• Low molecular weight and high ionization at milk pH
• High water solubility with minimal protein binding
• Lipid solubility and low pKa

Correct Answer: High protein binding and large volume of distribution

Q11. Which combination best predicts significant drug removal by hemodialysis?

• Low molecular weight, low protein binding, and low volume of distribution
• High lipophilicity and high volume of distribution
• Extensive hepatic metabolism with active metabolites
• Marked enterohepatic recycling

Correct Answer: Low molecular weight, low protein binding, and low volume of distribution

Q12. Which interaction reduces oral bioavailability via chelation in the gut?

• Tetracyclines taken with calcium or iron
• Grapefruit juice with nifedipine
• Rifampin with cyclosporine
• Omeprazole with ketoconazole

Correct Answer: Tetracyclines taken with calcium or iron

Q13. What is the primary mechanism of grapefruit juice–drug interaction?

• Inhibits intestinal CYP3A4, increasing bioavailability
• Induces hepatic CYP3A4, decreasing bioavailability
• Forms insoluble chelates with basic drugs
• Raises gastric pH, enhancing weak acid absorption

Correct Answer: Inhibits intestinal CYP3A4, increasing bioavailability

Q14. Cigarette smoking can necessitate higher doses of which drug due to CYP1A2 induction?

• Theophylline
• Warfarin
• Digoxin
• Lithium

Correct Answer: Theophylline

Q15. Which route best avoids first-pass hepatic metabolism?

• Sublingual
• Oral
• Intramuscular
• Rectal always avoids first-pass

Correct Answer: Sublingual

Q16. In shock or severe hypotension, which administration route shows the most unpredictable absorption?

• Intramuscular
• Intravenous
• Inhalational
• Transdermal

Correct Answer: Intramuscular

Q17. In hypoalbuminemia, what happens to highly albumin-bound acidic drugs (e.g., phenytoin)?

• Higher free fraction increases effect/toxicity at the same total concentration
• Lower free fraction reduces pharmacologic effect
• No change in free fraction or clinical effect
• Renal clearance of protein-bound drug markedly increases

Correct Answer: Higher free fraction increases effect/toxicity at the same total concentration

Q18. Therapeutic drug monitoring (TDM) is most useful for:

• Narrow therapeutic index drugs with variable pharmacokinetics
• Over-the-counter antacids
• Beta-lactam antibiotics with wide safety margins (routine use)
• Topical corticosteroids

Correct Answer: Narrow therapeutic index drugs with variable pharmacokinetics

Q19. Which genetic variants primarily guide initial warfarin dose individualization?

• CYP2C9 and VKORC1 variants
• CYP2D6 ultrarapid metabolizer status
• NAT2 slow acetylator status
• TPMT polymorphism

Correct Answer: CYP2C9 and VKORC1 variants

Q20. An unusual, often genetically determined, dose-independent response (e.g., G6PD deficiency hemolysis) is termed:

• Idiosyncratic reaction
• Type I hypersensitivity
• Tolerance
• Placebo effect

Correct Answer: Idiosyncratic reaction

Q21. Rapid reduction in drug response after repeated doses over a short period (e.g., nitrates) is called:

• Tachyphylaxis
• Type II hypersensitivity
• Supersensitivity
• Cumulative toxicity

Correct Answer: Tachyphylaxis

Q22. For aminoglycosides in obese patients, which weight descriptor is commonly used for dose calculation?

• Adjusted body weight
• Total body weight in all cases
• Ideal body weight only
• Body mass index

Correct Answer: Adjusted body weight

Q23. How can fever affect dosing with transdermal systems?

• Fever can increase cutaneous blood flow and enhance drug absorption
• Fever always decreases renal clearance of all drugs
• Fever abolishes CYP-mediated metabolism
• Fever has no clinically relevant effect on pharmacokinetics

Correct Answer: Fever can increase cutaneous blood flow and enhance drug absorption

Q24. Which factor is most likely to reduce oral bioavailability by increasing first-pass metabolism?

• Strong CYP3A induction by rifampin
• Delayed gastric emptying
• Enteric coating of tablets
• Crushing a sustained-release formulation

Correct Answer: Strong CYP3A induction by rifampin

Q25. A drug has a half-life of 8 hours. Which dosing interval minimizes peak–trough fluctuation for maintenance therapy?

• Every 8 hours
• Every 24 hours
• Once weekly
• Every 48 hours

Correct Answer: Every 8 hours

Q26. Which condition most clearly necessitates reducing doses of renally eliminated drugs like vancomycin?

• Acute kidney injury
• Hyperthyroidism
• Hemorrhoids
• Mild intermittent asthma

Correct Answer: Acute kidney injury

Q27. Older adults often require lower benzodiazepine doses primarily due to:

• Increased CNS sensitivity and decreased clearance
• Increased muscle mass
• Reduced body fat
• Increased glomerular filtration rate

Correct Answer: Increased CNS sensitivity and decreased clearance

Q28. Which factor most reduces activation of codeine to morphine?

• CYP2D6 poor metabolizer phenotype
• CYP2D6 ultrarapid metabolizer phenotype
• St John’s wort (CYP3A4 induction)
• High-protein diet

Correct Answer: CYP2D6 poor metabolizer phenotype

Q29. Which dosing change is appropriate for high hepatic-extraction drugs in moderate-to-severe liver disease?

• Reduce maintenance dose to account for decreased clearance
• Increase loading dose regardless of volume changes
• Avoid dose changes for prodrugs
• Prefer drugs with extensive first-pass extraction

Correct Answer: Reduce maintenance dose to account for decreased clearance

Q30. What is the safest initial dosing strategy for drugs with a narrow therapeutic index?

• Start low, go slow, with close clinical and laboratory monitoring
• Begin at the maximum recommended dose
• Ignore potential drug–drug interactions
• Skip baseline laboratory assessments

Correct Answer: Start low, go slow, with close clinical and laboratory monitoring

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