PLAB 2 Prescribing Safety & Emergency Management 2 — Questions and Answers
Question 1: A 35-year-old woman has a blood pressure of 180/115 on booking at 8 weeks gestation. She has no proteinuria. What is the most likely diagnosis and first-line antihypertensive?
- Pre-eclampsia — treat with labetalol
- Chronic hypertension (pre-existing, presenting before 20 weeks) — first-line antihypertensives in pregnancy are labetalol, nifedipine, or methyldopa (Correct answer)
- Gestational hypertension — no treatment needed
- Pre-eclampsia — treat with amlodipine
Correct answer: Chronic hypertension (pre-existing, presenting before 20 weeks) — first-line antihypertensives in pregnancy are labetalol, nifedipine, or methyldopa
Hypertension before 20 weeks (or pre-pregnancy) is chronic hypertension. Pre-eclampsia presents after 20 weeks. Safe antihypertensives in pregnancy: labetalol (first-line for chronic hypertension), nifedipine (second line), methyldopa (safe but side effects). ACE inhibitors and ARBs are contraindicated in pregnancy.
Question 2: A patient presents with a blood glucose of 28 mmol/L, bicarbonate of 10 mmol/L, pH 7.15, blood ketones of 4.8 mmol/L, and is vomiting. What is the diagnosis and initial management?
- Hyperosmolar hyperglycaemic state — aggressive IV fluids
- Diabetic ketoacidosis (DKA) — IV fluids (0.9% NaCl), insulin infusion (0.1 unit/kg/hr), potassium replacement, monitoring, and treat precipitant (Correct answer)
- Euglycaemic ketoacidosis — stop all insulin
- Lactic acidosis — IV bicarbonate
Correct answer: Diabetic ketoacidosis (DKA) — IV fluids (0.9% NaCl), insulin infusion (0.1 unit/kg/hr), potassium replacement, monitoring, and treat precipitant
DKA: hyperglycaemia (>11 mmol/L or known diabetes), ketonaemia (≥3 mmol/L blood ketones), acidosis (pH <7.3 or HCO3 <15). Management (JBDS guidelines): IV 0.9% NaCl resuscitation; fixed-rate IV insulin infusion 0.1 unit/kg/hr; potassium replacement (if K+ <5.5 mmol/L); glucose monitoring hourly; seek and treat precipitant; consider VTE prophylaxis.
Question 3: A junior doctor is about to prescribe trimethoprim for a UTI in a patient already taking phenytoin. What is the key drug interaction?
- Trimethoprim reduces phenytoin absorption
- Trimethoprim inhibits renal tubular secretion of creatinine (raising measured creatinine without affecting actual GFR) — this is not a true drug interaction with phenytoin but trimethoprim can increase phenytoin levels by inhibiting metabolism (Correct answer)
- There is no significant interaction
- Trimethoprim causes phenytoin toxicity by displacing it from protein binding
Correct answer: Trimethoprim inhibits renal tubular secretion of creatinine (raising measured creatinine without affecting actual GFR) — this is not a true drug interaction with phenytoin but trimethoprim can increase phenytoin levels by inhibiting metabolism
Trimethoprim can inhibit CYP2C9/CYP2C19, increasing phenytoin plasma levels and risking phenytoin toxicity (ataxia, nystagmus, confusion). In addition, trimethoprim artificially elevates serum creatinine (without true GFR change) by competing with creatinine for tubular secretion. Monitor phenytoin levels and for signs of toxicity.
Question 4: In the prescribing safety assessment context, which of the following is an example of a 'never event' in medication?
- Prescribing a suboptimal dose of antibiotic
- Administering 10 times the intended dose of IV potassium chloride (concentrated KCl) causing cardiac arrest (Correct answer)
- Prescribing a statin to a patient with dyslipidaemia without checking LFTs
- Failing to prescribe a laxative with an opioid
Correct answer: Administering 10 times the intended dose of IV potassium chloride (concentrated KCl) causing cardiac arrest
'Never events' are serious, wholly preventable patient safety incidents. Medication never events include: IV administration of concentrated potassium chloride; wrong route administration (e.g., intrathecal vincristine); misidentification of patients during medication administration; and insulin pump overdose. Policies require concentrated KCl to be stored and prepared by pharmacy, never on wards.
Question 5: A patient is prescribed gentamicin for a urinary tract infection with sepsis. After the third dose, serum creatinine has risen from 80 to 140 µmol/L. What should you do?
- Increase the dose to compensate for reduced renal drug clearance
- Stop gentamicin, reassess the patient, consider an alternative antibiotic, and monitor renal function — rising creatinine indicates nephrotoxicity (Correct answer)
- Continue gentamicin but reduce the frequency
- Ignore the creatinine rise as it is expected with gentamicin
Correct answer: Stop gentamicin, reassess the patient, consider an alternative antibiotic, and monitor renal function — rising creatinine indicates nephrotoxicity
Rising creatinine in a patient on gentamicin indicates acute kidney injury, likely aminoglycoside nephrotoxicity (tubular toxicity). Gentamicin should be stopped, the patient reassessed clinically, renal function monitored, and an alternative antibiotic prescribed if required. Pre- and post-dose levels should be checked throughout treatment to prevent toxicity.
Question 6: A 70-year-old woman is prescribed warfarin. Her GP has also recently started her on amiodarone. Her INR is now 7.8 and she has no signs of bleeding. What is the most appropriate management?
- Administer IV vitamin K 10mg immediately and admit to hospital
- Withhold warfarin for 1–2 doses, give low-dose oral vitamin K (1–2mg), recheck INR in 1–2 days, and adjust warfarin dose when amiodarone effect is stable (Correct answer)
- Continue warfarin at the same dose and recheck INR in 1 week
- Stop warfarin permanently and start a DOAC
Correct answer: Withhold warfarin for 1–2 doses, give low-dose oral vitamin K (1–2mg), recheck INR in 1–2 days, and adjust warfarin dose when amiodarone effect is stable
Amiodarone is a potent inhibitor of warfarin metabolism (CYP2C9), dramatically increasing INR. For INR 5–8 with no bleeding: withhold warfarin, give low-dose oral vitamin K (1–2mg), recheck INR in 24–48 hours. When amiodarone is started with warfarin, the warfarin dose typically needs reducing by 30–50% and more frequent INR monitoring is required.
PLAB 2 Prescribing Safety & Emergency Management 2
A 35-year-old woman has a blood pressure of 180/115 on booking at 8 weeks gestation.
She has no proteinuria.
What is the most likely diagnosis and first-line antihypertensive?