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

St John's Wort is a potent inducer of CYP3A4, CYP2C9, and P-glycoprotein, significantly reducing plasma concentrations of drugs such as cyclosporin, oral contraceptives, antiretrovirals, and warfarin.

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

Furanocoumarins in grapefruit juice irreversibly inhibit intestinal CYP3A4 and inhibit OATP transporters, reducing first-pass metabolism and increasing bioavailability of susceptible drugs such as simvastatin, felodipine, and cyclosporin.

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

Metronidazole inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation when alcohol is ingested, producing the characteristic disulfiram-like reaction.

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

Aspirin use in children during viral infections (influenza, varicella) is associated with Reye's syndrome, characterised by acute liver failure and encephalopathy, though the exact mechanism is not fully elucidated.

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

ACE inhibitors block angiotensin II, which is critical for fetal renal development from the second trimester onward; use leads to oligohydramnios, fetal renal failure, limb contractures, pulmonary hypoplasia and death.

CAOP - Competency Assessment of Overseas Pharmacist Practice Test

CAOP - Competency Assessment of Overseas Pharmacist Practice Test

CAOP Drug Interactions and Contraindications 3