Pharmacology in Surgery Flashcards

A patient on warfarin requires emergency surgery for a perforated duodenal ulcer. What is the most appropriate method to rapidly reverse the anticoagulation?

Answer: Prothrombin complex concentrate (PCC) and intravenous vitamin K

For emergency reversal of warfarin, UK guidelines (BCSH) recommend prothrombin complex concentrate (PCC, e.g., Beriplex/Octaplex) combined with IV vitamin K (5 mg). PCC provides immediate replacement of vitamin K-dependent factors (II, VII, IX, X), while IV vitamin K ensures sustained reversal. FFP is second-line if PCC is unavailable. Oral vitamin K alone takes 24-48 hours.

Which class of antibiotic acts by inhibiting bacterial cell wall synthesis through binding to penicillin-binding proteins?

Answer: Beta-lactams

Beta-lactam antibiotics (penicillins, cephalosporins, carbapenems, monobactams) all contain a beta-lactam ring that binds to penicillin-binding proteins (PBPs) — transpeptidases involved in cross-linking peptidoglycan in the bacterial cell wall. This inhibits cell wall synthesis, leading to osmotic lysis. Resistance occurs through beta-lactamase production or PBP modification.

A patient develops malignant hyperthermia during general anaesthesia. Which drug is the specific treatment?

Answer: Dantrolene

Dantrolene is the specific treatment for malignant hyperthermia (MH). It acts directly on skeletal muscle by binding to the ryanodine receptor (RYR1), reducing calcium release from the sarcoplasmic reticulum. MH is triggered by volatile anaesthetic agents and suxamethonium in genetically susceptible individuals (RYR1 mutations). The dose is 2.5 mg/kg IV, repeated as needed.

Which of the following analgesic drugs inhibits both serotonin and noradrenaline reuptake in addition to being a weak opioid agonist?

Answer: Tramadol

Tramadol has a dual mechanism of action: it is a weak mu-opioid receptor agonist AND inhibits reuptake of serotonin (5-HT) and noradrenaline. This dual mechanism makes it effective for both nociceptive and neuropathic pain. However, it carries a risk of serotonin syndrome when combined with other serotonergic drugs (SSRIs, MAOIs) and lowers the seizure threshold.

A patient with renal impairment (eGFR 20 ml/min) requires thromboprophylaxis post-operatively. Which low molecular weight heparin dose adjustment is recommended?

Answer: Reduce dose or use unfractionated heparin instead

LMWHs (enoxaparin, dalteparin, tinzaparin) are predominantly renally excreted. In severe renal impairment (eGFR <30 ml/min), there is significant accumulation risk leading to bleeding. UK guidelines recommend either dose reduction (e.g., enoxaparin 20 mg daily instead of 40 mg) or switching to unfractionated heparin, which is cleared by the reticuloendothelial system and is safer in renal failure.

Which local anaesthetic has the longest duration of action and is most commonly used for post-operative regional nerve blocks?

Answer: Bupivacaine

Bupivacaine is an amide-type local anaesthetic with the longest duration of action (4-8 hours, or up to 12 hours with adrenaline). It is widely used for epidural, spinal, and peripheral nerve blocks for post-operative analgesia. Its main risk is cardiotoxicity — it has high affinity for cardiac sodium channels. Levobupivacaine (the S-enantiomer) has a better cardiac safety profile.