High Yield Pharmacology: MRCEM Primary questions with answers

High Yield Pharmacology collects drug safety knowledge in one place. It covers drug toxicity and antidotes, a summary of drugs and their side effects, and poisoning, overdose and toxidromes. Pharmacology carries 24 of the 180 questions in MRCEM Primary. Overdose and poisoning are common emergency presentations, and recognising a toxidrome early can lead you to the correct antidote.

5 free questions below, each with the answer and the full explanation · 215 in the full bank · Last updated after the 27 October 2026 MRCEM Primary sitting.

1. Question 1 · High Yield Pharmacology

   A male aged 65 presents to the ED with frequent urination, especially at night, difficulty initiating urination, and a sensation of incomplete bladder emptying. On physical examination, his prostate is enlarged, smooth, and non-tender. He is diagnosed with benign prostatic hyperplasia (BPH). Which of the following medications can help relieve bladder spasms and provide symptom relief in this patient?

   1. ATamsulosin
   2. BFinasteride
   3. CHyoscine
   4. DSilodosin
   5. EDoxazosin
   Show answer and explanation

   Answer: C. Hyoscine is an anticholinergic that relaxes bladder smooth muscle, relieving spasm and urgency.

   • A: Alpha-blocker relieving obstruction, not bladder spasm.
   • B: 5-alpha reductase inhibitor shrinks the prostate over months.
   • D: Alpha-blocker relieving obstruction, not bladder spasm.
   • E: Alpha-blocker relieving obstruction, not bladder spasm.

   Full explanation

   • Hyoscine, an anticholinergic agent, is effective in relaxing bladder smooth muscle, reducing spasms, and relieving urinary urgency often associated with BPH.
   • Tamsulosin an alpha-blocker is more commonly used to relieve obstruction and increase urine flow.
   • finasteride (a 5-alpha reductase inhibitor) is more commonly used to reduce prostate size and relieve obstruction.

   High Yield:

   Side Effects of Anti-Cholinergic (Muscarinic) agent:

   Mnemonic: “BCDU”

   • Blurred Vision
   • Constipation
   • Dry Mouth
   • Urinary Retention

2. Question 2 · Poisoning, Overdose and toxidromes

   A man aged 60 takes an overdose of his regular medications. Bedside testing reveals hypoglycemia.
   Which drug is the most likely cause?

   1. AGlibenclamide
   2. BCitalopram
   3. CBisoprolol
   4. DMetformin
   5. EPrednisolone
   Show answer and explanation

   Answer: A. Glibenclamide is a sulfonylurea that stimulates insulin release, so overdose commonly causes hypoglycaemia.

   • B: SSRI; does not typically cause hypoglycaemia.
   • C: Beta-blocker; may mask hypoglycaemia but does not usually cause it.
   • D: Biguanide; rarely causes hypoglycaemia alone.
   • E: Corticosteroid; causes hyperglycaemia.

   Full explanation

   Glibenclamide (also known as glyburide) is an oral antidiabetic medication belonging to the class of sulfonylureas, which stimulate insulin secretion from the pancreas. Overdose or excessive use of glibenclamide can lead to significant hypoglycemia, especially in older adults or those with compromised liver function.

   The other options are less likely to cause hypoglycemia:

   • Bisoprolol: A beta-blocker that is primarily used for hypertension and heart failure, but it does not cause hypoglycemia.
   • Citalopram: An antidepressant that does not typically affect blood glucose levels.
   • Metformin: Generally, does not cause hypoglycemia by itself; it primarily reduces hepatic glucose production.
   • Prednisolone: A corticosteroid that can increase blood glucose levels.

3. Question 3 · Summary of drugs and their side effects

   Which of the following anti-tubercular drugs is a potent CYP450 enzyme inducer?

   1. ARifampicin
   2. BPyrazinamide
   3. CIsoniazid
   4. DStreptomycin
   5. EEthambutol
   Show answer and explanation

   Answer: A. Rifampicin is a potent inducer of cytochrome P450 enzymes.

   • B: Causes hepatotoxicity and hyperuricaemia, not CYP induction.
   • C: Causes hepatitis and peripheral neuritis; not the potent inducer.
   • D: Causes ototoxicity and nephrotoxicity.
   • E: Causes optic neuritis.

   Full explanation: Summary of drugs and their side effects

   Summary Of Drugs And Their Side Effects

4. Question 4 · Drugs toxicity and antidotes

   A patient aged 49 is sent into ED by his GP with jaundice and pruritus. Blood tests show a raised conjugated bilirubin. Urine tests show raised urinary bilirubin with absent urobilinogen. Which of the following drugs is most likely to cause this picture:

   1. AAbciximab
   2. BAspirin
   3. CDigoxin
   4. DLansoprazole
   5. ECo-amoxiclav
   Show answer and explanation

   Answer: E. Co-amoxiclav causes cholestatic jaundice, giving conjugated hyperbilirubinaemia with bilirubinuria and absent urobilinogen.

   • A: An antiplatelet; not a typical cause of cholestatic jaundice.
   • B: Not a typical cause of cholestatic jaundice.
   • C: Not a recognised cause of cholestasis.
   • D: Rarely implicated; co-amoxiclav is the classic cause.

   Full explanation: Penicillins

   Mechanism of Action

   Penicillins are beta-lactam antibiotics that inhibit bacterial cell wall synthesis by inactivating bacterial transpeptidases and preventing the cross-linking of peptidoglycan polymers that is essential for bacterial cell wall integrity. This results in loss of rigidity and a susceptibility to rupture. The major cause of resistance is the production of beta-lactamases (penicillinases) that are produced by certain strains of bacteria.

   Penicillins diffuse well into body tissues and fluids, but penetration into the cerebrospinal fluid is poor except when the meninges are inflamed.

   Side Effects

   Common side effects include: Anaphylaxis; angioedema; diarrhoea (very common, occurs most commonly with broad-spectrum antibiotics, may be associated with colitis); fever; hypersensitivity reactions; joint pains; rashes; serum sickness-like reaction; urticaria

   Rare side effects include: Cerebral irritation (may result from excessively high doses or in patients with severe renal failure); CNS toxicity (including convulsions); coagulation disorders; encephalopathy; haemolytic anaemia; interstitial nephritis; leucopenia; thrombocytopenia

   Allergy

   The most important side effect of the penicillins is hypersensitivity which can be fatal.

   Penicillin allergy is a potentially serious adverse reaction which can be life threatening. It is the most commonly noted drug allergy in the UK, reported by about 10% of the population. It is estimated, however, that only around 20% of those reporting penicillin allergy are truly allergic.

   Patients with a history of anaphylaxis, urticaria, or rash immediately after penicillin use should not receive a penicillin or other beta-lactam antibiotics; about 0.5 – 6.5 % of penicillin-sensitive patients will also be allergic to the cephalosporins.

   Patients with a history of a more minor rash (i.e. non-confluent, non-pruritic rash restricted to a small area of the body) or delayed reaction (rash occurring more than 72 hours after penicillin administration), may not be truly allergic and may be considered for penicillin or beta-lactam treatment in severe infection (although possibility of allergy should be borne in mind). Other beta-lactam antibiotics (including cephalosporins) can be used in these patients.

   Indications

   First Line Antibiotic	Indications
   Ampicillin or amoxicillin	Blind therapy for native valve endocarditis; endocarditis caused by enterococci (with low-dose gentamicin); endocarditis caused by HACEK organisms (with low-dose gentamicin); blind treatment of meningitis in adults > 50 years (with cefotaxime/ceftriaxone); meningitis caused by Listeria (with gentamicin); otitis media; sinusitis; oral infection; exacerbation chronic bronchitis; low-severity community acquired pneumonia; moderate-severity community acquired pneumonia (with clarithromycin)
   Co-amoxiclav	Severe or resistant otitis media; resistant sinusitis; severe or resistant dental infection; high-severity community acquired pneumonia (with clarithromycin); hospital acquired pneumonia (non severe signs or symptoms and not at higher risk of resistance); animal and human bite wounds
   Flucloxacillin	Native valve endocarditis caused by staphylococci; prosthetic valve endocarditis caused by staphylococci (with rifampicin and low-dose gentamicin); spreading/severe otitis externa; osteomyelitis; septic arthritis; widespread impetigo; severe erysipelas; cellulitis; mastitis during breastfeeding
   Benzylpenicillin	Meningococcal disease (prehospital); endocarditis caused by streptococci (with or without low-dose gentamicin); endocarditis caused by enterococci (with low-dose gentamicin); meningitis caused by meningococci; erysipelas
   Phenoxymethylpenicillin	Erysipelas, acute tonsillitis
   Piperacillin/tazobactam	Community acquired septicaemia, hospital acquired septicaemia; peritonitis; hospital acquired pneumonia (severe signs or symptoms or at higher risk of resistance); complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen

   Benzylpenicillin

   Benzylpenicillin sodium remains an important and useful antibiotic but is inactivated by bacterial beta-lactamases. It is effective for many streptococcal (including pneumococcal), gonococcal, and meningococcal infections and also for anthrax, diphtheria, gas-gangrene, and leptospirosis. Pneumococci, meningococci, and gonococci which have decreased sensitivity to penicillin have been isolated; benzylpenicillin sodium is no longer the drug of first choice for pneumococcal meningitis. Although benzylpenicillin sodium is effective in the treatment of tetanus, metronidazole is preferred. Benzylpenicillin is inactivated by gastric acid and absorption from the gastrointestinal tract is low; therefore it must be given by injection.

   If meningococcal disease (meningitis with non-blanching rash or meningococcal septicaemia) suspected, benzylpenicillin sodium should be given before transfer to hospital, so long as this does not delay the transfer. If a patient with suspected bacterial meningitis without non-blanching rash cannot be transferred to hospital urgently, benzylpenicillin sodium should be given before the transfer.

   Phenoxymethylpenicillin

   Phenoxymethylpenicillin (penicillin V) is less active than benzylpenicillin but has a similar antibacterial spectrum. It is gastric-acid stable and therefore suitable for oral administration, but should not be used for serious infections because absorption can be unpredictable and plasma concentrations variable.

   It is given primarily for respiratory tract infections in children, for streptococcal tonsillitis and for continuing treatment after one or more injections of benzylpenicillin when clinical response has begun. It is also used for prophylaxis against streptococcal infections following rheumatic fever and against pneumococcal infections following splenectomy or in sickle-cell disease. It should not be used for meningococcal or gonococcal infections.

   Flucloxacillin

   Flucloxacillin is unique in that it is beta-lactamase stable and it can be used in infections caused by beta-lactamase producing staphylococci e.g. S. aureus. It is acid-stable and can therefore be given by mouth as well as by injection.

   It is used first line for treatment of widespread impetigo infection, cellulitis, mastitis, osteomyelitis, septic arthritis, severe erysipelas, severe/spreading otitis externa and infective endocarditis caused by staphylococci.

   The most common adverse effects of flucloxacillin include nausea, vomiting, skin rash, and diarrhoea. Cholestatic jaundice and hepatitis may occur very rarely, up to two months after treatment with flucloxacillin has been stopped. Administration for more than 2 weeks and increasing age are risk factors.

   Ampicillin

   Ampicillin is active against certain Gram-positive and Gram-negative organisms but is inactivated by penicillinases. Ampicillin is associated with high levels of resistance, therefore it is often not appropriate for blind treatment of infection. It is principally indicated for the treatment of exacerbations of chronic bronchitis and middle ear infections, both of which may be due to Streptococcus pneumoniae and H. influenzae, and for urinary tract infections.

   Maculopapular rashes commonly occur with ampicillin (and amoxicillin) but are not usually related to true penicillin allergy. They almost always occur in patients with glandular fever; thus broad-spectrum penicillins should not be used for blind treatment of a sore throat. The risk of rash is also increased in patients with acute or chronic lymphocytic leukaemia or in cytomegalovirus infection.

   Amoxicillin

   Amoxicillin is a derivative of ampicillin and has a similar antibacterial spectrum. It is better absorbed than ampicillin when given orally, producing higher plasma and tissue concentrations; unlike ampicillin, absorption is not affected by the presence of food in the stomach. The adverse effects of amoxicillin are mainly gastrointestinal and mild and include nausea, vomiting and diarrhoea.

   Amoxicillin is used first line for low to moderate severity community acquired pneumonia, exacerbations of chronic bronchitis, for acute otitis media, for acute sinusitis, for oral infections/dental abscess, for Listeria meningitis (in combination with another antibiotic), for infective endocarditis (in combination with another antibiotic) and for H. Pylori eradication (in combination with metronidazole/clarithromycin and a proton pump inhibitor).

   Co-amoxiclav

   Co-amoxiclav consists of amoxicillin with the beta-lactamase inhibitor clavulanic acid. Clavulanic acid itself has no significant antibacterial activity but, by inactivating beta-lactamases, it makes the combination active against beta-lactamase-producing bacteria that are resistant to amoxicillin. These include resistant strains of Staph. aureus, E. coli, and H. influenzae, as well as many Bacteroides and Klebsiella spp, causing infections such as respiratory tract infections, bone, joint and soft tissue infections, genitourinary and abdominal infection. Co-amoxiclav should be reserved for infections likely, or known, to be caused by amoxicillin-resistant beta-lactamase-producing strains.

   The most common adverse effects of co-amoxiclav include nausea, vomiting, skin rash and diarrhoea. Pseudomembranous colitis should be considered if a person develops severe diarrhoea during or after treatment with co-amoxiclav. Cholestatic jaundice can occur either during or shortly after the use of co-amoxiclav. An epidemiological study has shown that the risk of acute liver toxicity was about 6 times greater with co-amoxiclav than with amoxicillin. Cholestatic jaundice is more common in patients above the age of 65 years and in men; these reactions have only rarely been reported in children. Jaundice is usually self-limiting and very rarely fatal.

   Antipseudomonal Penicillins

   Piperacillin, a ureidopenicillin, is only available in combination with the beta-lactamase inhibitor tazobactam. Ticarcillin, a carboxypenicillin, is only available in combination with the beta-lactamase inhibitor clavulanic acid. Both preparations have a broad spectrum of activity against a range of Gram-positive and Gram-negative bacteria, and anaerobes. Piperacillin with tazobactam has activity against a wider range of Gram-negative organisms than ticarcillin with clavulanic acid and it is more active against Pseudomonas aeruginosa. These antibacterials are not active against MRSA. They are used in the treatment of septicaemia, hospital-acquired pneumonia, and complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen. For severe pseudomonas infections these antipseudomonal penicillins can be given with an aminoglycoside (e.g. gentamicin) since they have a synergistic effect.

5. Question 5 · High Yield Pharmacology

   A female aged 60 is admitted to the emergency department with signs of increased intracranial pressure (ICP). You decide to give 150 mL of 3% hypertonic saline as part of her treatment. How much sodium chloride (NaCl) is present in the 150 mL of 3% hypertonic saline?

   1. A4.5 grams
   2. B3 grams
   3. C7.5 grams
   4. D6 grams
   5. E2.25 grams
   Show answer and explanation

   Answer: A. 3% saline contains 3 g per 100 mL, so 150 mL contains 3 x 1.5 = 4.5 g.

   • B: That is the amount in 100 mL, not 150 mL.
   • C: Would require 250 mL of 3% saline.
   • D: Would require 200 mL of 3% saline.
   • E: That is the amount in 75 mL of 3% saline.

   Full explanation

   • 3% hypertonic saline contains 3 grams of sodium chloride (NaCl) per 100 mL.
   • To calculate for 150 mL:
   • 3 grams/ 100ml × 150 = 4.5grams
   • Note:9% Normal Saline contains 0.9 grams of Nacl in 100 ml.