PSA Prescribing in Special Populations 2 — Questions and Answers
Question 1: An 80-year-old patient with CrCl 25 mL/min is prescribed gentamicin for a severe infection. What is the most important prescribing consideration?
- Reduce the dose and extend the dosing interval (Correct answer)
- Increase the dose to achieve therapeutic levels
- Use standard dosing as renal function rarely affects aminoglycosides
- Switch to an oral aminoglycoside
Correct answer: Reduce the dose and extend the dosing interval
Aminoglycosides are renally cleared and nephrotoxic; dose reduction and extended dosing intervals are essential in renal impairment to avoid accumulation and toxicity.
Question 2: A 70-year-old woman with type 2 diabetes is prescribed metformin. Her eGFR is 30 mL/min/1.73m². What is the most appropriate action?
- Discontinue metformin due to risk of lactic acidosis (Correct answer)
- Continue at full dose as benefits outweigh risks
- Double the dose to compensate for reduced absorption
- Switch to insulin immediately
Correct answer: Discontinue metformin due to risk of lactic acidosis
Metformin is contraindicated when eGFR falls below 30 mL/min/1.73m² due to accumulation and risk of lactic acidosis.
Question 3: Which drug is MOST likely to require dose reduction in a patient with severe hepatic impairment?
- Ramipril
- Morphine (Correct answer)
- Cetirizine
- Metformin
Correct answer: Morphine
Morphine undergoes extensive hepatic metabolism; severe hepatic impairment reduces its clearance, leading to accumulation and increased risk of toxicity.
Question 4: An 85-year-old patient on warfarin is given a new prescription for ibuprofen. What is the most significant prescribing concern?
- Reduced warfarin absorption
- Increased bleeding risk and potential renal impairment (Correct answer)
- Ibuprofen accelerates warfarin metabolism
- Warfarin toxicity due to reduced protein binding
Correct answer: Increased bleeding risk and potential renal impairment
NSAIDs inhibit platelet function and increase GI bleeding risk while also potentially causing renal impairment, particularly dangerous in elderly patients on warfarin.
Question 5: A patient with CrCl 15 mL/min requires regular analgesia. Which opioid should be used with the most caution?
- Fentanyl
- Morphine (Correct answer)
- Buprenorphine
- Hydromorphone
Correct answer: Morphine
Morphine's active metabolite morphine-6-glucuronide accumulates in renal failure, causing prolonged sedation and respiratory depression.
Question 6: An elderly patient is prescribed digoxin for atrial fibrillation. Which age-related factor most increases their risk of digoxin toxicity?
- Increased hepatic blood flow in the elderly
- Reduced renal clearance of digoxin (Correct answer)
- Increased GI absorption with advancing age
- Reduced protein binding of digoxin
Correct answer: Reduced renal clearance of digoxin
Digoxin is primarily renally eliminated; age-related decline in renal function reduces its clearance and increases accumulation and toxicity risk.
Question 7: A 75-year-old on amlodipine and simvastatin is started on clarithromycin for a chest infection. What is the most important drug interaction concern?
- Clarithromycin reduces amlodipine absorption
- Clarithromycin inhibits CYP3A4, raising simvastatin levels and increasing risk of myopathy (Correct answer)
- Amlodipine increases clarithromycin toxicity
- Simvastatin reduces clarithromycin efficacy
Correct answer: Clarithromycin inhibits CYP3A4, raising simvastatin levels and increasing risk of myopathy
Clarithromycin is a potent CYP3A4 inhibitor and can markedly raise simvastatin plasma concentrations, increasing the risk of myopathy and rhabdomyolysis.
PSA Prescribing in Special Populations 2
An 80-year-old patient with CrCl 25 mL/min is prescribed gentamicin for a severe infection.
What is the most important prescribing consideration?