CAOP Drug Interactions and Contraindications 3

Question 1

St John's Wort (Hypericum perforatum) is contraindicated with numerous prescription medications because it:

Accepted Answer

Induces CYP3A4 and P-glycoprotein, reducing plasma levels of many drugs

Answer

Inhibits CYP3A4, markedly increasing plasma levels of co-administered drugs

Answer

Inhibits MAO-A and MAO-B simultaneously, causing tyramine accumulation

Answer

Increases renal prostaglandin synthesis, reducing drug excretion

Question 2

Grapefruit juice increases the bioavailability of certain drugs primarily by:

Accepted Answer

Inhibiting intestinal CYP3A4 and OATP1B1, reducing first-pass metabolism and hepatic uptake

Answer

Increasing gastric pH, enhancing drug absorption

Answer

Stimulating P-glycoprotein to retain drugs longer in enterocytes

Answer

Chelating minerals that would otherwise reduce drug absorption

Question 3

A patient on metronidazole consumes alcohol and develops flushing, tachycardia, nausea and vomiting. This reaction is best described as:

Accepted Answer

Disulfiram-like reaction due to aldehyde dehydrogenase inhibition

Answer

Anaphylactic reaction due to a shared structural epitope

Answer

Serotonin syndrome due to combined MAO inhibition

Answer

Cholinergic crisis due to acetylcholinesterase inhibition

Question 4

Aspirin is contraindicated in children under 16 years with viral illnesses because of the risk of:

Accepted Answer

Reye's syndrome, a rare but potentially fatal encephalopathy and hepatopathy

Answer

Haemophilia exacerbation due to platelet inhibition

Answer

Salicylate-induced nephrotic syndrome in developing kidneys

Answer

Stevens-Johnson syndrome triggered by viral-drug immune complexes

Question 5

ACE inhibitors are classified as Category D in pregnancy and should be avoided particularly from the second trimester because they:

Accepted Answer

Reduce fetal renal perfusion, causing oligohydramnios, renal tubular dysplasia and fetal death

Answer

Cause fetal cardiac neural crest defects in the first trimester only

Answer

Induce uterine contractions leading to premature labour

Answer

Cross the placenta and cause neonatal hyperglycaemia

Question 6

Co-administration of trimethoprim with methotrexate poses a significant risk of:

Accepted Answer

Severe bone marrow suppression due to additive antifolate effects

Answer

Crystalluria and acute renal failure due to drug precipitation

Answer

Stevens-Johnson syndrome due to shared sulfonamide hypersensitivity

Answer

Serotonin syndrome due to combined inhibition of tryptophan metabolism

Question 7

Enzyme-inducing antiepileptic drugs (e.g., phenytoin, carbamazepine) reduce the effectiveness of combined oral contraceptives because they:

Accepted Answer

Induce hepatic CYP3A4 and CYP2C9, increasing first-pass metabolism of contraceptive steroids

Answer

Inhibit estrogen and progesterone receptors in endometrial tissue

Answer

Reduce gastrointestinal transit time, decreasing contraceptive absorption

Answer

Block FSH and LH receptor binding, interfering with the contraceptive mechanism