Key points
- Single-best-answer vignettes on mechanisms, adverse effects, interactions and prescribing, in the style of licensing and final exams.
- Topics: pharmacokinetics, enzyme induction and inhibition, antibiotics, anticoagulants, antihypertensives, diabetes drugs, analgesics, antidotes and drugs in pregnancy.
- Each explanation says why the answer is right and why the other options are wrong.
- Always check a current formulary for doses. These questions test principles, not dosing.
Questions
1. A patient taking warfarin is started on rifampicin for tuberculosis. What happens to the INR, and why?
A. It rises because rifampicin inhibits CYP enzymes
B. It falls because rifampicin induces CYP enzymes
C. It does not change
D. It rises because rifampicin displaces warfarin from albumin only
E. It falls because rifampicin binds warfarin in the gut
Answer: B. Rifampicin is a strong inducer of hepatic cytochrome P450 enzymes, so warfarin is cleared faster and the INR falls, which risks clots. The dose of warfarin needs to rise with close monitoring. The effect lasts for weeks after rifampicin is stopped. Rifampicin also reduces the effect of oral contraceptives.
2. Which antidote is correct for paracetamol overdose?
A. Naloxone
B. N-acetylcysteine
C. Flumazenil
D. Atropine
E. Vitamin K
Answer: B. N-acetylcysteine replenishes glutathione and prevents the toxic metabolite NAPQI from damaging liver cells. It works best within 8 to 10 hours of ingestion, and treatment decisions use the time of ingestion and the plasma level. Naloxone is for opioids, flumazenil for benzodiazepines, atropine for organophosphates and vitamin K for warfarin.
3. A patient on lisinopril develops a persistent dry cough. What is the mechanism, and what is the usual next step?
A. Bradykinin accumulation; switch to an angiotensin receptor blocker
B. Histamine release; add an antihistamine
C. Beta-receptor blockade; stop treatment
D. Aldosterone excess; add spironolactone
E. Allergy to the drug; use a higher dose
Answer: A. ACE inhibitors reduce breakdown of bradykinin, which causes a dry cough in a minority of patients. Angiotensin receptor blockers do not affect bradykinin and are the usual alternative. Rare angioedema also arises from bradykinin and is a reason to stop the drug for good.
4. A 28-year-old woman at 10 weeks of pregnancy has epilepsy. Which antiepileptic has the highest risk of neural tube defects and should be avoided where possible?
A. Lamotrigine
B. Levetiracetam
C. Sodium valproate
D. Carbamazepine at the lowest dose only
E. All antiepileptics have equal risk
Answer: C. Valproate carries the highest risk of major malformations and neurodevelopmental problems, so it should be avoided in women who could become pregnant unless there is no alternative. Lamotrigine and levetiracetam have the lowest risk. High-dose folic acid is advised before conception for women on antiepileptics.
5. A man with a penicillin allergy that caused anaphylaxis has cellulitis. Which statement is correct?
A. Cefalexin is always safe
B. Avoid all beta-lactams unless the allergy has been formally assessed; use an alternative such as clarithromycin or doxycycline
C. Amoxicillin is safe because it is not penicillin
D. Flucloxacillin is the best choice
E. Gentamicin alone is first line
Answer: B. Penicillins, cephalosporins and carbapenems share a beta-lactam ring, and cross-reactivity is greatest after a severe immediate reaction. Amoxicillin and flucloxacillin are penicillins. A macrolide or doxycycline gives reasonable alternative cover for skin infection where local protocols allow.
6. Which drug is a competitive inhibitor of the vitamin K epoxide reductase pathway, and what monitors its effect?
A. Heparin; APTT
B. Warfarin; INR
C. Rivaroxaban; INR only
D. Aspirin; bleeding time
E. Alteplase; platelet count
Answer: B. Warfarin inhibits vitamin K epoxide reductase, so factors II, VII, IX and X are not activated, and the effect is monitored by the INR. Unfractionated heparin works through antithrombin and is monitored by APTT. Direct oral anticoagulants such as rivaroxaban need no routine INR monitoring.
7. A patient taking metformin is going for contrast CT, and their eGFR is 25 mL/min. What is the concern?
A. Hypoglycaemia
B. Lactic acidosis
C. Diabetes insipidus
D. Hypernatraemia
E. Thyroid storm
Answer: B. Metformin accumulates when the kidneys fail and can cause lactic acidosis, so it is withheld around contrast studies in patients with severely reduced renal function. Metformin alone rarely causes hypoglycaemia. Sulfonylureas and insulin are the drugs that do.
8. A 70-year-old on a loop diuretic and digoxin has nausea, visual disturbance with yellow-green halos and a pulse of 40. What electrolyte disturbance increases the risk of this toxicity?
A. Hyperkalaemia
B. Hypokalaemia
C. Hypernatraemia
D. Hypocalcaemia
E. Hypermagnesaemia
Answer: B. Hypokalaemia, often from loop diuretics, increases digoxin binding to the sodium-potassium ATPase and the risk of toxicity. Hypercalcaemia and hypomagnesaemia also add risk. Severe toxicity is treated with digoxin-specific antibody fragments. Digoxin has a narrow therapeutic index and is excreted by the kidneys.
9. A patient with type 2 diabetes and established heart failure needs an additional drug that reduces heart failure admissions. Which class has this evidence?
A. Sulfonylureas
B. SGLT2 inhibitors
C. Thiazolidinediones
D. Dipeptidyl peptidase-4 inhibitors always
E. Insulin glargine only
Answer: B. SGLT2 inhibitors (for example empagliflozin and dapagliflozin) reduce heart failure hospitalisation and slow chronic kidney disease progression. Thiazolidinediones cause fluid retention and are contraindicated in heart failure. They carry a risk of genital fungal infection and, rarely, euglycaemic ketoacidosis.
10. An opioid is given for severe pain. Which side effect does tolerance not develop to, so a laxative is prescribed with it?
A. Respiratory depression
B. Nausea
C. Constipation
D. Sedation
E. Euphoria
Answer: C. Tolerance develops to nausea, sedation and respiratory depression, but not to constipation, so a stimulant laxative should be prescribed with regular opioids. Pinpoint pupils also persist. Naloxone reverses respiratory depression in overdose and may need repeating because its effect is shorter than that of many opioids.
11. A patient develops a fever, muscle rigidity, confusion and a high creatine kinase soon after starting haloperidol. What is the likely diagnosis?
A. Serotonin syndrome
B. Neuroleptic malignant syndrome
C. Malignant hyperthermia
D. Anticholinergic toxicity
E. Tetanus
Answer: B. Neuroleptic malignant syndrome follows dopamine antagonism and causes fever, lead-pipe rigidity, autonomic instability and raised creatine kinase. Stop the antipsychotic and give supportive care, and consider dantrolene or bromocriptine. Serotonin syndrome features clonus and hyperreflexia and follows serotonergic drugs.
12. Which diuretic has the main action on the thick ascending limb of the loop of Henle?
A. Spironolactone
B. Hydrochlorothiazide
C. Furosemide
D. Acetazolamide
E. Mannitol
Answer: C. Loop diuretics such as furosemide block the sodium-potassium-2-chloride cotransporter in the thick ascending limb. Thiazides act on the distal convoluted tubule and spironolactone acts on the collecting duct. Acetazolamide inhibits carbonic anhydrase in the proximal tubule.
13. A woman taking the combined oral contraceptive pill is prescribed a drug for a seizure disorder and becomes pregnant. Which drug most likely caused contraceptive failure?
A. Levetiracetam
B. Carbamazepine
C. Gabapentin
D. Lamotrigine at all doses
E. Diazepam
Answer: B. Carbamazepine, phenytoin and phenobarbital induce hepatic enzymes and speed up the metabolism of oestrogen and progestogen, so the pill may fail. A non-hormonal or higher-dose alternative is advised. Levetiracetam and gabapentin are not significant inducers.
14. A patient on a monoamine oxidase inhibitor eats a large amount of mature cheese and develops a severe headache and a blood pressure of 220/120 mmHg. What causes this?
A. Excess histamine release
B. Tyramine-induced noradrenaline release
C. Serotonin deficiency
D. Dopamine depletion
E. Insulin surge
Answer: B. Monoamine oxidase normally breaks down dietary tyramine in the gut. When it is inhibited, tyramine displaces noradrenaline from nerve terminals and causes a hypertensive crisis. Patients must avoid aged cheese, cured meats and fermented foods. Combining these drugs with serotonergic drugs can cause serotonin syndrome.
15. What is the half-life rule for reaching steady state when a drug is given repeatedly?
A. One half-life
B. Two half-lives
C. About four to five half-lives
D. Ten half-lives
E. Steady state is never reached
Answer: C. With regular dosing, plasma concentration reaches about 94 to 97% of steady state after four to five half-lives. A loading dose can be used to reach an effective level sooner. Drugs with long half-lives take a long time to wash out after stopping.
References
- Rang and Dale's Pharmacology. Elsevier.
- Katzung's Basic and Clinical Pharmacology. McGraw-Hill.
- British National Formulary.
- World Health Organization Model List of Essential Medicines.