PLAB 1 Pharmacology & Prescribing

Question 1

A patient with atrial fibrillation is started on warfarin. Which of the following drugs, if added, would most significantly increase the risk of bleeding by inhibiting warfarin metabolism?

Accepted Answer

Fluconazole

Answer

Fluconazole is a potent inhibitor of CYP2C9, the main enzyme responsible for warfarin metabolism. This significantly increases warfarin levels and bleeding risk. Rifampicin, carbamazepine, and St John's Wort are inducers of CYP enzymes and would reduce warfarin efficacy.

Question 2

A 70-year-old woman with heart failure is started on spironolactone. Which electrolyte abnormality must be monitored closely?

Accepted Answer

Hyperkalaemia

Answer

Spironolactone is a potassium-sparing diuretic (aldosterone antagonist). It causes potassium retention, risking hyperkalaemia, which can cause life-threatening arrhythmias. Regular U&E monitoring is essential, especially if the patient is also on ACE inhibitors or ARBs which also raise potassium.

Question 3

A patient with type 2 diabetes has an eGFR of 25 ml/min/1.73m². Which diabetes medication must be stopped or dose-reduced due to risk of lactic acidosis?

Accepted Answer

Metformin

Answer

Metformin is contraindicated when eGFR falls below 30 ml/min/1.73m² due to the risk of lactic acidosis (accumulation of metformin due to impaired renal excretion). NICE guidelines recommend stopping metformin if eGFR < 30 and dose reduction if eGFR 30–45.

Question 4

A 25-year-old woman presents 2 hours after taking 20 paracetamol tablets (10g). She is asymptomatic. Serum paracetamol level is above the treatment line on the nomogram. What is the most appropriate treatment?

Accepted Answer

IV N-acetylcysteine (NAC)

Answer

IV N-acetylcysteine (NAC) is the antidote for paracetamol overdose. It replenishes glutathione, which is depleted by the toxic metabolite NAPQI, preventing hepatocellular damage. Treatment should be started when the level plots above the treatment line on the Rumack-Matthew nomogram. Activated charcoal may also be given within 1 hour of ingestion.

Question 5

Which antibiotic is contraindicated in pregnant women due to the risk of 'grey baby syndrome' in neonates?

Accepted Answer

Chloramphenicol

Answer

Chloramphenicol inhibits mitochondrial protein synthesis. Neonates lack adequate hepatic glucuronyl transferase to metabolise it, leading to accumulation and 'grey baby syndrome' (circulatory collapse, abdominal distension, cyanosis, death). It is avoided in pregnancy and neonates.

PLAB 1 Practice Test

PLAB 1 Practice Test

PLAB 1 Pharmacology & Prescribing