Wattle Pharmacy Prep

Dosing in special populations
Practice questions with explanations

Dosing in special populations belongs to Pharmacokinetics and pharmacodynamics, which makes up about 10% of the Overseas Pharmacist Readiness Assessment (OPRA®). Answer each question yourself before opening the explanation.

1. Which consideration applies when prescribing for a patient in the last days of life?

  1. Continue all previous medicines
  2. Add preventive therapy
  3. Simplify to essential symptom control medicines, change route as swallowing fails, and stop those with no immediate benefit
  4. No changes are needed
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C. Simplify to essential symptom control medicines, change route as swallowing fails, and stop those with no immediate benefit

Subcutaneous administration replaces oral as swallowing fails, and anticipatory medicines for pain, breathlessness, nausea, agitation and secretions are prescribed in advance. Preventive medicines are stopped, and the reasoning explained so that families do not experience the change as care being withdrawn.

2. Which factor most affects drug handling in a neonate compared with an older child?

  1. Immature hepatic conjugation and renal function, with higher body water and lower protein binding
  2. Complete maturity of all elimination pathways at birth
  3. Faster hepatic metabolism than adults
  4. Higher body fat proportion
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A. Immature hepatic conjugation and renal function, with higher body water and lower protein binding

Glucuronidation is markedly immature at birth and matures over months, which is why chloramphenicol caused grey baby syndrome and why morphine clearance is low in neonates. Glomerular filtration is also low and rises over the first year. Beyond infancy, children often clear drugs faster per kilogram than adults, so dosing changes direction with age.

3. How should the dose of a renally cleared drug be approached in a patient with rapidly changing renal function?

  1. Use the last available creatinine as accurate
  2. Estimates based on a single creatinine are unreliable, so dosing is conservative with frequent reassessment and concentration monitoring where available
  3. Use the eGFR from six months ago
  4. Renal function changes do not affect dosing
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B. Estimates based on a single creatinine are unreliable, so dosing is conservative with frequent reassessment and concentration monitoring where available

Creatinine lags behind an acute change by a day or more, so in evolving acute kidney injury the calculated clearance overestimates true function, sometimes grossly. Dosing in that setting is guided by trend, urine output, clinical state and drug concentrations, and the situation is rechecked daily rather than treated as a fixed calculation.

These are 3 of the 33 questions on dosing in special populations in the app.

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More topics in Pharmacokinetics and pharmacodynamics

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