PLAB 1 Pharmacology & Prescribing 2 — Questions and Answers
Question 1: A 65-year-old man is prescribed gentamicin for a Gram-negative infection. Which of the following side effects must be specifically monitored?
- Hepatotoxicity and jaundice
- Nephrotoxicity and ototoxicity (Correct answer)
- Pulmonary fibrosis
- QT prolongation
Correct answer: Nephrotoxicity and ototoxicity
Aminoglycosides (gentamicin, amikacin) cause nephrotoxicity (tubular damage) and ototoxicity (vestibular and cochlear damage), particularly with prolonged use or high trough levels. Regular monitoring of renal function and gentamicin levels (trough and peak, or once-daily AUC monitoring) is essential.
Question 2: A patient on long-term oral steroids (prednisolone) requires co-prescription of which of the following to prevent a common serious side effect?
- Calcium and vitamin D supplementation plus bisphosphonate (Correct answer)
- Anticoagulation with warfarin
- Prophylactic antifungal therapy
- H2 receptor antagonist for gastric protection only
Correct answer: Calcium and vitamin D supplementation plus bisphosphonate
Long-term corticosteroids cause significant bone loss (osteoporosis) through multiple mechanisms. NICE guidelines (CG146) recommend calcium and vitamin D for all patients on steroids, and bisphosphonates (e.g., alendronate) for patients at moderate/high risk of fracture. This is one of the most important co-prescriptions in clinical practice.
Question 3: A patient with asthma develops worsening bronchoconstriction after being prescribed a new medication for hypertension. Which class of drug is most likely responsible?
- ACE inhibitor
- Beta-blocker (Correct answer)
- Calcium channel blocker
- Thiazide diuretic
Correct answer: Beta-blocker
Beta-blockers (even cardioselective ones like atenolol) are contraindicated in asthma because they can cause bronchospasm by blocking beta-2 receptors in bronchial smooth muscle. Non-selective beta-blockers (propranolol) carry greater risk. This is a key prescribing safety rule.
Question 4: A 28-year-old woman of childbearing age with epilepsy is prescribed valproate. What is the most important counselling point?
- She must avoid alcohol completely
- Valproate is highly teratogenic (risk of neural tube defects, neurodevelopmental effects) and must not be used in women who may become pregnant without specialist review and the Pregnancy Prevention Programme (Correct answer)
- She must avoid dairy products
- She should double the dose if she misses one tablet
Correct answer: Valproate is highly teratogenic (risk of neural tube defects, neurodevelopmental effects) and must not be used in women who may become pregnant without specialist review and the Pregnancy Prevention Programme
Sodium valproate has high teratogenic risk — 10% risk of congenital malformations (especially neural tube defects) and 30–40% risk of neurodevelopmental problems. UK MHRA requires implementation of the Pregnancy Prevention Programme (contraception, annual review, patient card) for all women of childbearing potential on valproate.
Question 5: A patient is prescribed trimethoprim for a UTI. They are also on methotrexate for rheumatoid arthritis. What is the key interaction?
- Trimethoprim increases methotrexate excretion
- Both are folate antagonists — co-administration markedly increases the risk of methotrexate toxicity (pancytopenia) (Correct answer)
- Trimethoprim reduces efficacy of methotrexate
- The combination increases the risk of tendon rupture
Correct answer: Both are folate antagonists — co-administration markedly increases the risk of methotrexate toxicity (pancytopenia)
Both trimethoprim and methotrexate are folate antagonists. Concurrent use markedly increases the risk of methotrexate toxicity — particularly haematological toxicity (bone marrow suppression, pancytopenia). This combination should be avoided; an alternative antibiotic should be prescribed.
Question 6: A 45-year-old man with a history of peptic ulcer disease requires an NSAID for acute gout. What should be co-prescribed to reduce the risk of GI complications?
- An antihistamine (H1 blocker)
- A proton pump inhibitor (PPI) (Correct answer)
- Metronidazole
- Misoprostol is preferred over PPI
Correct answer: A proton pump inhibitor (PPI)
NSAIDs inhibit COX-1 and COX-2, reducing gastric mucosal protection and increasing the risk of peptic ulcers and GI bleeding. PPI co-prescription is recommended by NICE for patients on NSAIDs who have risk factors (previous ulcer, age >65, oral steroids, anticoagulants). A PPI reduces GI complications significantly.
PLAB 1 Pharmacology & Prescribing 2
A 65-year-old man is prescribed gentamicin for a Gram-negative infection.
Which of the following side effects must be specifically monitored?