Respiratory pharmacology: MRCEM Primary questions with answers

Respiratory pharmacology brings together the drugs used for airway disease and allergy. It covers antihistamines, bronchodilators and corticosteroids, then applies them to the management of asthma in adults and of anaphylaxis. Pharmacology carries 24 of the 180 questions in MRCEM Primary. Both conditions are time-critical emergencies, and choosing the right drug, dose and route can change the outcome.

5 free questions below, each with the answer and the full explanation · 68 in the full bank · Last updated after the 27 October 2026 MRCEM Primary sitting.

1. Question 1 · Anti-histamine drugs

   Regarding the pathophysiology of asthma, which one of the following neurotransmitters plays an important role in bronchoconstriction?

   1. AAcetylcholine
   2. BSerotonin
   3. CHistamine
   4. DAnticholinergic
   5. EGABA
   Show answer and explanation

   Answer: C. Histamine released from mast cells contributes to bronchoconstriction in asthma.

   • A: Acetylcholine mediates parasympathetic tone; histamine is the mast-cell mediator asked about.
   • B: Serotonin is not a key bronchoconstrictor mediator in asthma.
   • D: Anticholinergic describes a drug class, not a mediator.
   • E: GABA is an inhibitory neurotransmitter with no role here.

   Full explanation: Anti-histamine drugs

   Anti histamine: 

   Block H1 histamine receptors

   Indications:

   • Allergic rhinitis
   •  Urticaria
   • Pruritis 
   • Insect bites and stings 
   •  Anaphylaxis 
   • Angioedema
   •  Nausea and vomiting 
   • Motion sickness and vertigo
   •  Insomnia

   Divided into 2 groups:

   Sedating anti-histamines	Non-Sedating antihistamines
   promethazine, alimemazine, chlorphenamine, cyclizine Older drugs crosses BBB cause drowsiness and psychomotor impairment Additional antimuscarinic effects: Urinary retention, dry mouth, blurred vision, GI disturbance. Used with Caution in prostatic hypertrophy, urinary retention, acute angle glaucoma	loratadine, cetirizine Newer drugs No antimuscarinic effects Do not cross BBB to any extent drowsiness and psychomotor impairment rare

2. Question 2 · Bronchodilator drugs

   A relatively higher dose of aminophylline is needed to reach therapeutic plasma concentration in which one of the following patients?

   1. AHepatic impairment
   2. BThose receiving cimetidine
   3. CSmokers
   4. DCongestive heart failure patients
   5. EInfection
   Show answer and explanation

   Answer: C. Smokers clear theophylline faster, so need higher doses.

   • A: Reduces clearance, raising levels.
   • B: Cimetidine inhibits metabolism, raising levels.
   • D: Reduces clearance, raising levels.
   • E: Infection raises levels.

   Full explanation: Bronchodilator drugs

   Bronchodilator therapy:

    

   Note: Important points of theophylline:

   • Theophylline has narrow window between therapeutic and toxic doses, and the half-life can be affected by a number of factors, making a therapeutic dose difficult to achieve. It is advised that serum levels of 10-20 mg/I six to eight hours after the last tablet should be aimed for.

   Factors that increase the half-life of theophylline include:

   • Heart failure
   •  Cirrhosis
   •  Viral infection
   • Drugs (Enzyme inhibitors)

   Factors that decrease the half-life of theophylline include:

   •  Smoking
   • Heavy drinking
   • Drugs (Enzyme inducers)

   Enzyme inducers and Enzyme inhibitors

   Enzyme inducers	Enzyme inhibitors
   Increasing the rate of metabolism and hepatic clearance of concurrently administered drugs, which typically results in a decreased pharmacologic effect.	Decrease hepatic clearance and increase pharmacologic effect.
   Useful mnemonic SCRAP GP Sulphonylureas Carbamazepine Rifampicin Alcohol Phenytoin Griseofulvin Phenobarbital	Useful mnemonic: SICKFACES.COM Sodium valproate Isoniazid Cimetidine Ketoconazole Fluconazole Alcohol Chloramphenicol Erythromycin Sulfonamides Ciprofloxacin Omeprazole Metronidazole

    

   Aminophylline:

   Aminophylline is a compound of theophylline with ethylenediamine in a 2:1 ratio. The ethylenediamine improves its solubility. It is less potent and shorter acting than theophylline.

   It is used in the treatment of:

   • Asthma
   • COPD
   • Heart failure
   • Bradycardias

   Note: Aminophylline has mild positive inotropic and chronotropic effects, producing an increase in cardiac output and a decrease in systemic vascular resistance, leading to a decrease in arterial blood pressure. It has been used historically in the treatment of refractory heart failure and is recommended by the current ALS guidelines as an alternative treatment for bradycardias.

3. Question 3 · Asthma in adults management

   A patient aged 19 with known asthma comes to ED himself with acute breathlessness and wheeze over the past 20 minutes. On examination he is tachypneic and tachycardic. His oxygen saturations are 96% on air. What is the first line treatment for acute asthma:

   1. APrednisolone
   2. BSalbutamol
   3. CIpratropium bromide
   4. DOxygen
   5. ESalmeterol
   Show answer and explanation

   Answer: B. High-dose inhaled short-acting beta2-agonists such as salbutamol are first line in acute asthma.

   • A: Important early, but bronchodilation comes first.
   • C: Added to a beta-agonist in severe disease or poor response.
   • D: Given only if hypoxaemic.
   • E: Long-acting beta-agonist, not used for acute relief.

   Full explanation: Asthma in adults management

   Levels of severity of acute asthma attacks in adults

    

   Moderate acute asthma	Increasing symptoms PEF >50–75% best or predicted No features of acute severe asthma
   Acute severe asthma	Any one of: PEF 33–50% best or predicted Respiratory rate ≥25/min Heart rate ≥110/min Inability to complete sentences in one breath
   Life-threatening asthma	Any one of the following in a patient with severe asthma: Clinical signs Altered conscious level PEF Exhaustion Arrhythmia Hypotension Cyanosis Silent chest Poor respiratory effort Measurements PEF <33% best predicted SpO2 <92% PaO2 <8kPa 'normal' PaCO2 (4.6–6.0 kPa)
   Near-fatal asthma	Raised PaCO2 and/or requiring mechanical ventilation with raised inflation pressures

    

    

   • Example -1 : In exam, if they give you a scenario that a 34-year-old asthma patient who is unable to complete a sentence in one breath, his HR is 115 beats/min and SpO2 91%. How would you classify the severity of asthma in this patient?
   • Answer: Life-threatening asthma
   • Explanation: Any patient with features of acute severe asthma along with any one feature of life-threatening asthma (as in above scenario his saturation is below <92%) would be classified as having life-threatening asthma.

    

   Management of acute asthma in adults in the emergency department

    

    

   Discharge plan

   • In all patients who received nebulized β2 bronchodilator prior to presentation, consider an extended observation period prior to discharge.
   • If PEF <50% on presentation, give prednisolone 40–50 mg/day until recovery (minimum 5 days).
   • In all patients ensure treatment supply of inhaled steroid and β2 bronchodilator and check inhaler technique
   • Arrange GP follow-up within 2 working days post-discharge.
   • Fax or email discharge letter to GP
   • Refer to asthma liaison nurse/chest clinic.

4. Question 4 · Respiratory pharmacology

   A patient attends ED with an urticarial rash. He has no lip/tongue swelling or difficulty breathing and there are no signs of shock. You are about to prescribe an antihistamine and he asks for a non-sedating antihistamine as he needs to get back to work. Which of the following is a non-sedating antihistamine:

   1. AFexofenadine
   2. BDiphenhydramine
   3. CHydroxyzine
   4. DChlorphenamine
   5. EPromethazine
   Show answer and explanation

   Answer: A. Fexofenadine is a second-generation, non-sedating antihistamine.

   • B: First-generation antihistamine; sedating.
   • C: First-generation antihistamine; sedating.
   • D: First-generation antihistamine; sedating.
   • E: First-generation antihistamine; markedly sedating.

   Full explanation: Antihistamines

   Antihistamines are competitive inhibitors at the H1-receptor (in contrast to H2 receptor antagonists used to decrease gastric acid secretion). They act to relax histamine-induced bronchoconstriction, block the vasodilator effect of histamine, inhibit histamine-induced increases in capillary permeability and block mucus secretion and sensory nerve stimulation.

   Pharmacokinetics

   Histamine (H1)-receptor antagonists are well absorbed after oral administration. The effects of these agents are usually seen in 30 minutes (with maximal effects at 1 – 2 h); the duration of action is 3 – 8 hours for first-generation compounds and 3 – 24 hours for second-generation compounds.

   H1-receptor antagonists are metabolised in the liver; many induce microsomal enzymes and alter their own metabolism and that of other drugs.

   Indications

   • Allergic rhinitis and conjunctivitis
   • Urticarial rashes, pruritus, insect bites and stings
   • Angioedema
   • Nausea/vomiting and prevention of motion sickness
   • Insomnia

   Chlorphenamine

   All older antihistamines cause sedation but alimemazine tartrate and promethazine may be more sedating whereas chlorphenamine maleate and cyclizine may be less so. This sedating activity is sometimes used to manage the pruritus associated with some allergies or used to manage occasional insomnia. There is little evidence that any one of the older, 'sedating' antihistamines is superior to another and patients vary widely in their response.

   Cetirizine

   The newer antihistamines e.g. cetirizine cause less sedation and psychomotor impairment than the older antihistamines because they are much less lipid soluble and penetrate the blood brain barrier only to a slight extent.

   Cautions

   Antihistamines should usually be avoided in acute porphyrias (although some antihistamines are thought to be safe).

   Antihistamines should be used with caution in epilepsy, prostatic hypertrophy, urinary retention, hepatic impairment and susceptibility to angle-closure glaucoma.

   Side Effects (significantly reduced with second-generation agents)

   Elderly patients and children are more susceptible to side effects.

   Common side effects of antihistamines may include:

   • Anticholinergic effects (blurred vision, dry mouth, urinary retention)
   • Headache
   • Gastrointestinal disturbances
   • Psychomotor impairment (sedation, dizziness and loss of appetite)

   Drowsiness may affect performance of skilled tasks (e.g. cycling or driving); sedating effects are enhanced by alcohol and opioid analgesics.

5. Question 5 · Corticosteroids

   Concerning steroids in the management of acute asthma in adults, which of these statements is INCORRECT:

   1. AIntravenous steroids are more effective at reducing relapses than oral steroids.
   2. BSteroids should be given in adequate doses to all patients with an acute asthma attack.
   3. COral steroids should be continued daily for at least 5 days following the acute attack.
   4. DThe earlier steroids are given in the acute attack, the better the outcome.
   5. EAt the end of the course of oral steroids, they can usually be stopped abruptly without tapering the dose.
   Show answer and explanation

   Answer: A. IV and oral steroids are equally effective, so IV is not better at reducing relapses.

   • B: BTS/SIGN advise adequate steroid doses for all patients.
   • C: Prednisolone is continued for at least 5 days or until recovery.
   • D: Earlier steroid administration gives better outcomes.
   • E: Short courses can be stopped without tapering.

   Full explanation: Corticosteroids

   Corticosteroids: 

   Corticosteroids are a class of steroid hormones that are naturally produced in the adrenal cortex as well as administered as medications for therapeutic purposes. We have already discussed naturally produced corticosteroids in physiology. Now we will discuss in detail pharmacology of administrated steroids.

   Naturally occurring Classes of corticosteroids: Glucocorticoids and mineralocorticoids, are involved in a wide range of physiological processes, including stress response, immune response, and regulation of inflammation.

   Classification of administrated steroids:

   Inhaled steroids: (beclomethasone, budesonide, fluticasone)

   Uses: Prophylaxis in chronic asthma if: Exacerbations in last 2 years requiring systemic corticosteroid or nebulized bronchodilator or B-agonists used more than twice per week or Symptoms disturb sleep more than twice per week.

   • Hay fever (Nasal spray)
   • COPD

   Side effects: Rare which include Oral candidiasis, hoarseness and sore mouth.

   Note:  In high doses systemic adverse effects can occur which include Adrenal suppression, Osteoporosis and Glaucoma.

    

   Oral and injectable corticosteroids:

   Oral and intravenous steroids: (prednisolone, dexamethasone, hydrocortisone).

   Specific uses: 

   Prednisolone: Has mainly glucocorticoid action 4 times more potent than hydrocortisone primary used for disease suppression in autoimmune/Rheumatoid conditions, Temporal arteritis, Asthma and acute adrenal insufficiency.

   Hydrocortisone: Short acting primarily known for its glucocorticoid activity, but it also possesses mineralocorticoid activity. Because of mineralocorticoid effect result into fluid retention means unsuitable for long-term treatment for disease suppression but is used long-term with fludrocortisone in adrenal suppression.

    Uses:

   • Adrenal insufficiency
   • Addison’s disease
   • Acute allergy 
   • Asthma 
   • Shock 
   • Angioedema 
   • Hypersensitivity reactions 
   •  Severe inflammatory bowel disease 
   •  Rheumatic disease

    

   Dexamethasone: Long acting primarily known for its very high glucocorticoid activity and insignificant mineralocorticoid activity.

   Uses: 

   • Cerebral oedema
   •  Perioperatively
   •  Inflammatory disorders
   •  Croup
   • Intractable nausea
   • Diagnosis of Cushing’s syndrome (Overnight Dexamethasone suppression test)
   • Temporal arteritis

   Side effects

   Patients on long-term steroid use are at risk of the following:

   • Adrenal suppression: In long-term use, e.g., prednisolone >7.5mg a day → adrenal atrophy due to corticotrophin suppression, therefore, withdraw steroid slowly to prevent Addisonian crisis
   • Steroids should be doubled in times of stress/illness (unless on high dose) because the body cannot respond to increased requirements, to prevent Addisonian crisis.
   • Infections: Due to the suppression of the inflammatory response patients are more susceptible to infection. Reactivation of dormant infections, e.g., TB, may occur.

   Complications:

   •  Patients who are not immune to chicken pox (not previously infected) are at risk of severe chicken pox, with complications such as encephalitis, pneumonia, and hepatitis. Varicella zoster immunoglobulin is required for postexposure prophylaxis; this provides passive immunity.
   • Patients should also be advised to avoid exposure to measles and should receive postexposure immunoglobulin within 72 hours if they are exposed.
   • All patients on long-term steroids should carry a ‘steroid card’ to inform medical practitioners that they are on steroids or have been on steroids (for up to a year as adrenal suppression can be prolonged).