Pharmacology Principles Flashcards
7 cards from real PSA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Pharmacology Principles flashcards as text
Rifampicin is a potent inducer of CYP3A4. A patient on long-term warfarin starts rifampicin for tuberculosis. What is the most likely clinical consequence?
Answer: Decreased INR due to increased warfarin metabolism
CYP3A4 induction by rifampicin accelerates warfarin metabolism, reducing plasma warfarin levels and anticoagulant effect, leading to a sub-therapeutic INR.
Fluoxetine inhibits CYP2D6. A patient taking fluoxetine is prescribed codeine for pain. What is the expected pharmacological outcome?
Answer: Reduced analgesic effect due to impaired conversion of codeine to morphine
Codeine requires CYP2D6-mediated conversion to morphine for its analgesic effect; CYP2D6 inhibition by fluoxetine reduces morphine production, diminishing analgesia.
Amiodarone inhibits CYP2C9. A patient stabilised on warfarin starts amiodarone. What monitoring and action is required?
Answer: Reduce warfarin dose and increase INR monitoring frequency
Amiodarone's CYP2C9 inhibition increases warfarin plasma levels, raising bleeding risk; warfarin dose reduction and close INR monitoring are required.
Which type of drug interaction describes two drugs producing an effect greater than the sum of their individual effects?
Answer: Synergistic (supra-additive) interaction
A synergistic interaction occurs when combined drug effects exceed the arithmetic sum of individual effects, as seen with some antibiotic combinations.
A patient on digoxin is started on erythromycin. Erythromycin inhibits P-glycoprotein (P-gp) intestinal efflux transporter. What is the clinical implication?
Answer: Increased digoxin absorption and risk of toxicity
P-glycoprotein normally limits digoxin intestinal absorption; inhibition by erythromycin increases digoxin bioavailability and plasma levels, raising toxicity risk.
ACE inhibitors and potassium-sparing diuretics (e.g., spironolactone) prescribed together risk which clinically dangerous interaction?
Answer: Pharmacodynamic — additive hyperkalemia
Both ACE inhibitors (reduce aldosterone) and potassium-sparing diuretics (block aldosterone) independently raise serum potassium, producing additive hyperkalemia when combined.
Grapefruit juice inhibits intestinal CYP3A4. A patient drinks grapefruit juice with their simvastatin. What is the expected effect?
Answer: Increased simvastatin bioavailability and increased risk of myopathy
Grapefruit juice inhibits intestinal CYP3A4 via furanocoumarins, reducing simvastatin first-pass metabolism and significantly increasing plasma levels and myopathy risk.