PLAB 1 Pharmacology and Therapeutics 2 — Questions and Answers
Question 1: A patient is prescribed amoxicillin for a chest infection. They mention they are also taking the combined oral contraceptive pill. According to current BNF guidance, does amoxicillin interact with the combined oral contraceptive?
- Yes — all antibiotics reduce the efficacy of the pill and additional contraception is always needed
- No — non-enzyme-inducing antibiotics like amoxicillin do not reduce the efficacy of the combined oral contraceptive according to current evidence and BNF guidance (Correct answer)
- Yes — amoxicillin specifically destroys oestrogen in the gut
- Antibiotics only interact with the progesterone-only pill
Correct answer: No — non-enzyme-inducing antibiotics like amoxicillin do not reduce the efficacy of the combined oral contraceptive according to current evidence and BNF guidance
Current BNF and FSRH guidance states that non-enzyme-inducing antibiotics (including amoxicillin) do not reduce the efficacy of the combined oral contraceptive. Only enzyme-inducing drugs (e.g., rifampicin, carbamazepine, phenytoin) require additional contraceptive precautions.
Question 2: A patient with chronic kidney disease stage 4 is found to have a potassium level of 6.8 mmol/L. ECG shows peaked T waves. What is the most important immediate treatment?
- Oral sodium polystyrene sulfonate (Calcium Resonium)
- IV calcium gluconate 10% to stabilise the myocardium, followed by insulin-dextrose infusion to reduce serum potassium (Correct answer)
- Oral calcium supplements
- Withhold all medications and recheck potassium in 24 hours
Correct answer: IV calcium gluconate 10% to stabilise the myocardium, followed by insulin-dextrose infusion to reduce serum potassium
Severe hyperkalaemia (>6.5 mmol/L) with ECG changes is a medical emergency. IV calcium gluconate is given first to stabilise the myocardium (does not reduce potassium). Insulin-dextrose drives potassium intracellularly. Nebulised salbutamol can also help. Calcium Resonium removes potassium but acts too slowly for acute management.
Question 3: According to NICE guidelines, what is the first-line antihypertensive for a 60-year-old Caucasian patient with no comorbidities?
- ACE inhibitor (e.g., ramipril)
- Calcium channel blocker (e.g., amlodipine) (Correct answer)
- Beta-blocker (e.g., bisoprolol)
- Thiazide-like diuretic (e.g., indapamide)
Correct answer: Calcium channel blocker (e.g., amlodipine)
NICE hypertension guidelines (NG136) recommend a calcium channel blocker (CCB) as first-line for patients aged ≥55 or of African/Caribbean descent. ACE inhibitors/ARBs are first-line for patients aged <55 (non-African/Caribbean). At age 60 without comorbidities, amlodipine would be appropriate.
Question 4: A patient taking co-amoxiclav develops profuse watery diarrhoea with abdominal pain 5 days into the course. Stool sample tests positive for Clostridioides difficile toxin. What is the first-line treatment?
- Continue co-amoxiclav and add loperamide
- Stop the causative antibiotic and start oral vancomycin (Correct answer)
- Start IV metronidazole as first-line
- No treatment needed — C. difficile resolves spontaneously
Correct answer: Stop the causative antibiotic and start oral vancomycin
Current UK guidelines recommend oral vancomycin as first-line treatment for C. difficile infection (replacing metronidazole, which is now second-line). The causative antibiotic should be stopped if possible. Loperamide is contraindicated as it can lead to toxic megacolon.
Question 5: A patient on long-term prednisolone 20 mg daily for rheumatoid arthritis wants to stop the medication. What is the correct approach?
- Stop immediately — there is no need for gradual withdrawal
- Gradual dose reduction is essential to avoid adrenal crisis, as long-term corticosteroids suppress the hypothalamic-pituitary-adrenal (HPA) axis (Correct answer)
- Halve the dose once and then stop
- Switch to a different steroid at the same dose before stopping
Correct answer: Gradual dose reduction is essential to avoid adrenal crisis, as long-term corticosteroids suppress the hypothalamic-pituitary-adrenal (HPA) axis
Long-term corticosteroid use (>3 weeks) suppresses the HPA axis. Abrupt withdrawal can cause adrenal crisis (hypotension, shock, death). The BNF recommends gradual dose tapering, typically reducing by 1-2.5 mg every 2-4 weeks, with monitoring for symptoms of adrenal insufficiency.
Question 6: A 72-year-old man with heart failure is prescribed spironolactone in addition to ramipril. What is the most important electrolyte to monitor closely with this combination?
- Sodium
- Potassium — both drugs can cause hyperkalaemia, and the combination significantly increases this risk (Correct answer)
- Calcium
- Magnesium
Correct answer: Potassium — both drugs can cause hyperkalaemia, and the combination significantly increases this risk
Both ACE inhibitors (ramipril) and aldosterone antagonists (spironolactone) can cause hyperkalaemia. The combination significantly increases the risk. NICE recommends checking potassium and renal function within 1 week of starting spironolactone, then regularly thereafter. Potassium >5.5 mmol/L requires dose adjustment or cessation.
PLAB 1 Pharmacology and Therapeutics 2
A patient is prescribed amoxicillin for a chest infection.
They mention they are also taking the combined oral contraceptive pill.
According to current BNF guidance, does amoxicillin interact with the combined oral contraceptive?