FRCS Pharmacology in Surgery 2

Question 1

A patient taking clopidogrel requires an elective total hip replacement. According to UK guidelines, how many days before surgery should clopidogrel ideally be stopped?

Accepted Answer

7 days

Answer

Clopidogrel irreversibly inhibits the P2Y12 ADP receptor on platelets for the platelet's lifespan (7-10 days). UK guidelines (NICE, AAGBI) recommend stopping clopidogrel 7 days before elective surgery to allow sufficient new platelet production. The decision must balance bleeding risk against thrombotic risk, particularly in patients with recent coronary stents.

Question 2

Which intravenous fluid most closely resembles the electrolyte composition of plasma and is recommended as first-line for fluid resuscitation in the UK?

Accepted Answer

Hartmann's solution (compound sodium lactate)

Answer

Hartmann's solution (Ringer's lactate/compound sodium lactate) contains Na+ 131, K+ 5, Ca2+ 2, Cl- 111, and lactate 29 mmol/L — closely matching plasma composition. NICE guidelines (CG174) recommend balanced crystalloids like Hartmann's as first-line for resuscitation. Normal saline has supraphysiological chloride (154 mmol/L), which can cause hyperchloraemic metabolic acidosis with large-volume use.

Question 3

Metformin should be withheld before surgery primarily because of the risk of which life-threatening complication?

Accepted Answer

Lactic acidosis

Answer

Metformin inhibits hepatic gluconeogenesis and mitochondrial complex I. In the perioperative period, reduced renal perfusion (from fasting, haemorrhage, or hypotension) impairs metformin clearance, leading to accumulation. This can precipitate type B lactic acidosis (mortality up to 50%). UK guidelines recommend omitting metformin on the day of surgery and restarting when eating and drinking normally with adequate renal function.

Question 4

Which antiemetic acts primarily as a serotonin 5-HT3 receptor antagonist and is commonly used for post-operative nausea and vomiting?

Accepted Answer

Ondansetron

Answer

Ondansetron is a selective 5-HT3 receptor antagonist that blocks serotonin at the chemoreceptor trigger zone and vagal afferents. It is widely used for PONV and chemotherapy-induced nausea. It has few sedative effects but can cause QT prolongation and constipation. Metoclopramide is a D2 antagonist, cyclizine is an H1 antagonist, and haloperidol is a D2 antagonist.

Question 5

A patient develops an anaphylactic reaction during induction of anaesthesia. What is the first-line drug treatment and route of administration?

Accepted Answer

Intramuscular adrenaline 500 micrograms (0.5 mg)

Answer

According to Resuscitation Council UK guidelines, intramuscular adrenaline (500 micrograms = 0.5 ml of 1:1000 in adults) is the first-line treatment for anaphylaxis. Adrenaline reverses bronchospasm (beta-2), supports blood pressure (alpha-1), and reduces mediator release from mast cells (beta-2). The IM route is preferred in most settings as IV adrenaline carries a risk of arrhythmia and requires careful titration.

FRCS Part A Practice Test

FRCS Part A Practice Test

FRCS Pharmacology in Surgery 2