CPJE CPJE Drug Interactions and Therapeutics 1 — Questions and Answers
Question 1: A patient on warfarin is prescribed ciprofloxacin. Which monitoring parameter should the pharmacist prioritize?
- INR/PT levels (Correct answer)
- Blood glucose
- Serum potassium
- Liver enzymes
Correct answer: INR/PT levels
Ciprofloxacin inhibits warfarin metabolism, increasing anticoagulant effect and bleeding risk, so INR must be monitored closely.
Question 2: Which drug combination is contraindicated due to the risk of serotonin syndrome?
- Sertraline and linezolid (Correct answer)
- Metformin and lisinopril
- Atorvastatin and amlodipine
- Omeprazole and clopidogrel
Correct answer: Sertraline and linezolid
Linezolid is an MAO inhibitor; combining it with SSRIs like sertraline can precipitate life-threatening serotonin syndrome.
Question 3: A patient taking simvastatin is started on clarithromycin. What is the primary concern?
- Increased risk of myopathy/rhabdomyolysis (Correct answer)
- Reduced antibiotic efficacy
- Hyperkalemia
- QT prolongation only
Correct answer: Increased risk of myopathy/rhabdomyolysis
Clarithromycin inhibits CYP3A4, dramatically increasing simvastatin levels and the risk of myopathy or rhabdomyolysis.
Question 4: Which interaction requires separating doses by at least 2 hours to prevent reduced drug absorption?
- Levothyroxine and calcium carbonate (Correct answer)
- Metoprolol and amlodipine
- Metformin and glipizide
- Lisinopril and furosemide
Correct answer: Levothyroxine and calcium carbonate
Calcium carbonate chelates levothyroxine in the GI tract, significantly reducing its absorption if taken simultaneously.
Question 5: A patient on lithium is prescribed ibuprofen for pain. What adverse outcome is most likely?
- Lithium toxicity due to elevated serum levels (Correct answer)
- Reduced lithium efficacy
- Additive CNS depression
- Hypokalemia
Correct answer: Lithium toxicity due to elevated serum levels
NSAIDs reduce renal prostaglandin synthesis, decreasing lithium clearance and raising serum lithium to toxic levels.
Question 6: Which mechanism explains the interaction between digoxin and amiodarone?
- Amiodarone inhibits P-glycoprotein, increasing digoxin levels (Correct answer)
- Amiodarone induces CYP2D6, decreasing digoxin levels
- Additive chronotropic effects reduce efficacy
- Amiodarone displaces digoxin from plasma proteins
Correct answer: Amiodarone inhibits P-glycoprotein, increasing digoxin levels
Amiodarone inhibits P-gp-mediated renal and intestinal elimination of digoxin, increasing its plasma concentration.
CPJE CPJE Drug Interactions and Therapeutics 1
A patient on warfarin is prescribed ciprofloxacin.
Which monitoring parameter should the pharmacist prioritize?