Dosing in obese patients MCQs With Answer

Dosing in obese patients MCQs With Answer

This quiz set is designed for M.Pharm students studying Clinical Pharmacokinetics and Therapeutic Drug Monitoring. Obesity alters physiology—affecting absorption, distribution, metabolism and elimination—and complicates dose selection for both hydrophilic and lipophilic drugs. These 20 multiple-choice questions focus on principles such as appropriate weight scalars (TBW, IBW, LBW, adjusted body weight), changes in volume of distribution and clearance, drug-class specific dosing strategies (aminoglycosides, vancomycin, anticoagulants, DOACs), and therapeutic drug monitoring considerations. Questions emphasize clinical reasoning and application of dosing formulas so students can optimize therapeutic outcomes and reduce toxicity in obese patients.

Q1. Which weight scalar is most appropriate to use when calculating an initial aminoglycoside dose in an obese adult?

• Total body weight (TBW)
• Ideal body weight (IBW)
• Lean body weight (LBW)
• Adjusted body weight (AdjBW)

Correct Answer: Adjusted body weight (AdjBW)

Q2. Obesity typically has which effect on the volume of distribution (Vd) for highly lipophilic drugs?

• Vd decreases due to increased adipose sequestration
• Vd remains unchanged regardless of lipophilicity
• Vd increases because adipose tissue provides an expanded distribution space
• Vd increases only if renal clearance is reduced

Correct Answer: Vd increases because adipose tissue provides an expanded distribution space

Q3. For vancomycin dosing in obese patients, the recommended approach for the initial loading dose is based on which weight?

• Ideal body weight (IBW)
• Total body weight (TBW)
• Lean body weight (LBW)
• Adjusted body weight (AdjBW)

Correct Answer: Total body weight (TBW)

Q4. Which formula modification is recommended when estimating creatinine clearance (Cockcroft-Gault) in an obese patient to avoid overestimation?

• Use TBW without modification
• Use IBW for all obese adults
• Use adjusted body weight (AdjBW) instead of TBW
• Use BMI directly in the Cockcroft-Gault equation

Correct Answer: Use adjusted body weight (AdjBW) instead of TBW

Q5. Which pharmacokinetic parameter is most likely to be increased in obesity leading to higher dosing requirements for some drugs?

• Fraction unbound in plasma for highly protein-bound drugs
• Renal clearance for all renally excreted drugs
• Volume of distribution for lipophilic drugs
• First-pass hepatic extraction uniformly for all drugs

Correct Answer: Volume of distribution for lipophilic drugs

Q6. Low molecular weight heparin (LMWH) such as enoxaparin is generally dosed in obese patients based on which weight, with special considerations at very high body weights?

• Ideal body weight (IBW) only
• Total body weight (TBW), with caution or adjustments above extreme weights
• Lean body weight (LBW) always
• Adjusted body weight (AdjBW) regardless of BMI

Correct Answer: Total body weight (TBW), with caution or adjustments above extreme weights

Q7. Which of the following is a valid clinical rationale for using adjusted body weight (AdjBW) instead of TBW or IBW?

• AdjBW accounts for the increased adipose-mediated clearance of hydrophilic drugs
• AdjBW assumes adipose tissue behaves identically to lean tissue for drug distribution
• AdjBW provides a compromise when TBW would overestimate and IBW would underestimate dosing for some hydrophilic drugs
• AdjBW is only used to estimate glomerular filtration rate (GFR)

Correct Answer: AdjBW provides a compromise when TBW would overestimate and IBW would underestimate dosing for some hydrophilic drugs

Q8. Therapeutic drug monitoring (TDM) in obese patients is particularly important for which reason?

• Obesity eliminates interpatient variability in pharmacokinetics
• Dosing recommendations for obesity are rigid and do not require monitoring
• Physiological changes in obesity can unpredictably alter exposure, increasing risk of toxicity or therapeutic failure
• TDM is required only for oral drugs in obesity

Correct Answer: Physiological changes in obesity can unpredictably alter exposure, increasing risk of toxicity or therapeutic failure

Q9. For hydrophilic antibiotics (e.g., beta-lactams), how does obesity generally affect dosing strategy?

• Use TBW-based loading and maintenance doses without adjustment
• Expect decreased Vd; therefore reduce dosing
• Use IBW or AdjBW for dosing because hydrophilic drugs distribute poorly into adipose tissue
• Dosing should always be doubled compared to non-obese patients

Correct Answer: Use IBW or AdjBW for dosing because hydrophilic drugs distribute poorly into adipose tissue

Q10. In obese patients, which change in hepatic clearance is commonly observed and may affect drugs with high hepatic extraction ratio?

• Consistent decrease in hepatic blood flow for all obese patients
• Potential increase in hepatic blood flow and fatty infiltration which can unpredictably modify clearance
• Complete loss of hepatic metabolic capacity
• No change in hepatic clearance across all drugs

Correct Answer: Potential increase in hepatic blood flow and fatty infiltration which can unpredictably modify clearance

Q11. Direct oral anticoagulants (DOACs) in patients with extreme obesity (e.g., >120 kg) are:

• Well studied and require no special considerations
• Often recommended at higher than-label doses
• Associated with limited evidence; use with caution and consider monitoring or alternative agents
• Contraindicated irrespective of indication

Correct Answer: Associated with limited evidence; use with caution and consider monitoring or alternative agents

Q12. Which weight descriptor correlates best with drug-metabolizing organ size and is sometimes used to scale clearance in obese patients?

• Total body weight (TBW)
• Body surface area (BSA)
• Lean body weight (LBW)
• Basal metabolic index (BMI)

Correct Answer: Lean body weight (LBW)

Q13. For vancomycin therapeutic drug monitoring in obesity, trough concentrations alone may be insufficient; what is a recommended alternative monitoring approach?

• Ignore levels and dose empirically
• Measure peak concentrations only
• Use AUC-guided dosing (AUC24/MIC) for more accurate exposure assessment
• Rely exclusively on clinical response without laboratory monitoring

Correct Answer: Use AUC-guided dosing (AUC24/MIC) for more accurate exposure assessment

Q14. Which statement about the fraction unbound (fu) of drugs in plasma in obese patients is most accurate?

• Fu is uniformly increased for all drugs in obesity
• Fu is unaffected by changes in plasma proteins such as albumin and alpha-1-acid glycoprotein
• Fu may change due to altered plasma protein concentrations, affecting free drug concentrations for highly protein-bound drugs
• Fu changes only for hydrophilic drugs

Correct Answer: Fu may change due to altered plasma protein concentrations, affecting free drug concentrations for highly protein-bound drugs

Q15. A clinician plans to administer a lipophilic sedative for general anesthesia in an obese patient. Which dosing consideration is most appropriate?

• Base the induction and maintenance doses purely on IBW
• Use TBW for bolus induction to account for increased Vd, but titrate maintenance to effect
• Avoid any dose changes and use standard non-obese dosing
• Use AdjBW for both bolus and infusion without monitoring

Correct Answer: Use TBW for bolus induction to account for increased Vd, but titrate maintenance to effect

Q16. Which of the following formulas is commonly used to calculate adjusted body weight (AdjBW)?

• AdjBW = IBW + 0.4 × (TBW − IBW)
• AdjBW = TBW × 0.75
• AdjBW = IBW × 2
• AdjBW = LBW − IBW

Correct Answer: AdjBW = IBW + 0.4 × (TBW − IBW)

Q17. In obesity, decreased gastric emptying and increased gastric pH primarily affect which pharmacokinetic phase?

• Distribution
• Absorption
• Metabolism
• Elimination

Correct Answer: Absorption

Q18. Which class of drugs often requires weight-based dosing and may need dose capping or monitoring adjustments in severe obesity to avoid toxicity?

• Statins at fixed doses
• Aminoglycosides and vancomycin
• Topical corticosteroids
• Inhaled bronchodilators

Correct Answer: Aminoglycosides and vancomycin

Q19. When converting a chronic oral drug dose from a normal-weight patient to an obese patient, the preferred approach is:

• Simply scale dose linearly by TBW for all drugs
• Use pharmacokinetic principles, appropriate weight scalar, and therapeutic monitoring to individualize dose
• Always reduce dose to IBW-based values
• Double the dose to account for larger body mass

Correct Answer: Use pharmacokinetic principles, appropriate weight scalar, and therapeutic monitoring to individualize dose

Q20. Which monitoring strategy is most helpful to guide dosing for narrow therapeutic index drugs in obese patients?

• Empiric fixed dosing without lab assessment
• Therapeutic drug monitoring with measurement of unbound drug concentrations or AUC when feasible
• Rely only on weight-based nomograms developed for non-obese populations
• Monitoring only clinical endpoints without laboratory support

Correct Answer: Therapeutic drug monitoring with measurement of unbound drug concentrations or AUC when feasible

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