Adverse Drug Reactions in the Emergency Department: Essential FRCEM SBA Practice Questions Explained

FRCEM SBA practice questions is a core part of UK Emergency Medicine practice. Adverse drug reactions (ADRs) are a daily clinical reality in UK emergency medicine and a consistent, high-yield theme in the FRCEM Single Best Answer examination. They sit at the intersection of pharmacology, acute medicine, and patient safety, making them fertile ground for well-constructed SBA stems that discriminate between candidates who truly understand mechanisms and those who have only surface-level recall. Getting this topic right is not simply an exam exercise. The BMJ-published landmark study by Pirmohamed et al. (2004) demonstrated that ADRs account for approximately 5 to 7% of all unplanned hospital admissions in the UK, that the majority are predictable, and that a substantial proportion are preventable. For the emergency physician, every drug a patient takes is a potential culprit, and systematic thinking about ADR classification directly improves clinical decision-making as well as exam performance.

Epidemiology and Clinical Significance in the ED

The scale of ADR-related harm in the NHS is substantial. Pirmohamed et al. identified that ADR-related admissions were more likely to be avoidable than other admissions, and that the median bed stay was eight days, imposing considerable cost. In the emergency department, the drug classes most frequently implicated in presentations include anticoagulants (warfarin and direct oral anticoagulants), NSAIDs, penicillins and cephalosporins, antiepileptics, cardiovascular agents (digoxin, antihypertensives), opioids, antipsychotics, and SSRIs. Risk is amplified in older patients, in those prescribed five or more regular medicines (polypharmacy), and in patients with renal or hepatic impairment, where altered drug metabolism and excretion shift the risk profile considerably.

Narrow therapeutic index drugs deserve particular attention because small changes in plasma concentration produce clinically significant toxicity. The canonical list for examination purposes includes warfarin, lithium, digoxin, phenytoin, methotrexate, and aminoglycosides. An FRCEM SBA clinical scenario involving confusion, tremor, and ataxia in a patient on lithium should trigger immediate consideration of toxicity, with renal function and drug level measurement as the investigation priority.

Classification Frameworks: Rawlins-Thompson and DoTS

Two classification systems appear in the RCEM curriculum and are regularly tested in FRCEM SBA practice questions. Understanding both prevents the common exam error of conflating them.

Rawlins-Thompson Classification

This framework, refined over decades and now extended to six types, remains the most widely cited in RCEM examinations.

• Type A (Augmented): Predictable, dose-dependent extensions of the drug’s pharmacological effect. They account for roughly 80% of all ADRs. Examples include warfarin-induced bleeding, opioid-induced respiratory depression, and beta-blocker-induced bradycardia. Management involves dose reduction or discontinuation.
• Type B (Bizarre): Unpredictable, not dose-dependent, frequently immunological or idiosyncratic. Less common but disproportionately severe. Examples include penicillin anaphylaxis, carbamazepine-associated Stevens-Johnson syndrome, and halothane hepatitis. The drug must usually be discontinued permanently.
• Type C (Chronic): Related to cumulative dose and long-term exposure. Examples include corticosteroid-induced osteoporosis and opioid-induced adrenal suppression.
• Type D (Delayed): Manifest after a prolonged latent period. Chemotherapy-induced secondary malignancy is the classical example.
• Type E (End of use): Reactions occurring on withdrawal. Benzodiazepine withdrawal seizures and SSRI discontinuation syndrome are ED-relevant examples.
• Type F (Failure): Unexpected failure of therapeutic effect, often related to drug interactions. Oral contraceptive failure with enzyme-inducing antiepileptics is a familiar clinical scenario.

DoTS Framework

The DoTS framework (Dose-relatedness, Time-course, Susceptibility) offers a more granular mechanistic classification and is referenced in the Royal College of Emergency Medicine curriculum as a tool for understanding and communicating ADR risk. It classifies reactions by whether they are toxic, collateral, or hypersensitivity in dose-relatedness; by their timing (early, intermediate, late, or withdrawal); and by patient susceptibility factors including age, sex, genetics, comorbidity, and polypharmacy. In the FRCEM SBA, DoTS terminology appears in questions testing whether candidates can explain why a particular patient is at heightened risk of a reaction that another patient taking the same drug would not experience.

High-Yield ADR Syndromes: ED Assessment and Management

Anaphylaxis and Anaphylactoid Reactions

Anaphylaxis is an IgE-mediated (Type I hypersensitivity) systemic reaction involving mast cell and basophil degranulation with release of histamine, tryptase, and leukotrienes. Anaphylactoid reactions are clinically indistinguishable but occur without prior sensitisation and via direct mast cell activation (for example, with radiocontrast media or opioids). The Resuscitation Council UK anaphylaxis guidelines, updated in 2021, define anaphylaxis as a severe, life-threatening generalised or systemic hypersensitivity reaction. Diagnosis is clinical: the triad of airway compromise, bronchospasm, and cardiovascular collapse in the context of allergen exposure is sufficient to treat without waiting for investigations.

First-line management is intramuscular adrenaline (epinephrine) 0.5 mg (0.5 mL of 1:1000) into the anterolateral thigh, with a repeat dose at five minutes if there is no improvement. Antihistamines and corticosteroids are adjuncts only and must never delay adrenaline. All patients receiving adrenaline for anaphylaxis should be observed for a minimum of six hours following resolution of symptoms due to the risk of biphasic anaphylaxis. Serum mast cell tryptase levels should be taken at 15 to 60 minutes from symptom onset, at one to two hours, and at 24 hours as a convalescent baseline, and this result should accompany the referral to the regional allergy service.

ACE Inhibitor-Induced Angioedema

This is a critically important FRCEM SBA clinical scenario because it is mechanistically distinct from allergic angioedema and is managed differently. ACE inhibitors prevent the breakdown of bradykinin, leading to accumulation and vasodilation of submucosal vessels. The reaction is bradykinin-mediated, not histamine-mediated. This means it does not respond to adrenaline, antihistamines, or corticosteroids, which is a direct and recurring point of examination. It may occur at any point during treatment, including years after initiation. Airway management is the priority. Icatibant (a bradykinin B2 receptor antagonist) and C1 esterase inhibitor concentrate are licensed treatments for hereditary angioedema and have been used off-label in ACE inhibitor angioedema. The NICE Clinical Knowledge Summary on angioedema and the RCEM curriculum module on angioedema in the emergency department both address this distinction. The ACE inhibitor must be permanently discontinued and a clear drug allergy alert documented. For further reading on the nuances of hereditary and acquired angioedema presentations, the lessons on Angioedema in the Emergency Department and Hereditary Angioedema in the Emergency Department available through the FRCEM Single Best Answer revision course at EM Learning Centre provide structured, curriculum-mapped coverage.

Serotonin Syndrome

Serotonin syndrome results from excess serotonergic activity at central and peripheral 5-HT1A and 5-HT2A receptors. It is a clinical diagnosis characterised by the Hunter criteria triad: neuromuscular abnormality (clonus, hyperreflexia, myoclonus), autonomic instability (hyperthermia, tachycardia, diaphoresis), and altered mental status. It is typically caused by combinations of serotonergic agents including SSRIs, SNRIs, MAOIs, tramadol, linezolid, methylene blue, and triptans. Severity ranges from mild to life-threatening. Management is supportive: remove the offending agent, provide sedation with benzodiazepines for agitation and myoclonus, control hyperthermia aggressively (it is the primary driver of end-organ damage), and consider cyproheptadine (a 5-HT2A antagonist) in moderate to severe cases, although evidence remains limited. FRCEM SBA candidates frequently conflate serotonin syndrome with neuroleptic malignant syndrome; the distinguishing features are temporal onset (hours for serotonin syndrome versus days for NMS), clonus and hyperreflexia (serotonin syndrome) versus lead-pipe rigidity (NMS), and causative drug class.

Neuroleptic Malignant Syndrome

NMS is a rare but potentially fatal reaction to dopamine receptor-blocking agents (antipsychotics) or to sudden withdrawal of dopaminergic therapy (levodopa). The clinical tetrad is hyperthermia, severe rigidity, altered consciousness, and autonomic instability. It develops over one to three days. Creatine kinase is typically markedly elevated. Management involves immediate cessation of the offending agent, aggressive cooling, IV fluid resuscitation, and haematological and renal monitoring for rhabdomyolysis-induced acute kidney injury. Dantrolene and bromocriptine are used in severe cases by specialist teams. This is a case requiring urgent liaison with toxicology or intensive care.

How the FRCEM SBA Examination Tests Adverse Drug Reactions

The FRCEM SBA examination maps directly to the RCEM curriculum, and ADRs appear across multiple domains including pharmacology, acute allergy, toxicology, and patient safety. Questions commonly test the following specific competencies.

First, classification: a stem will describe a reaction and ask for the correct Rawlins-Thompson type, or will ask candidates to identify which drug class is most likely responsible for a given presentation. Second, mechanism: questions distinguish between IgE-mediated, bradykinin-mediated, and direct mast cell-activating reactions, each requiring a different management approach. Third, management priorities: the FRCEM SBA frequently presents a scenario where the distractor answers include antihistamines or corticosteroids as the first-line treatment for anaphylaxis, testing whether candidates correctly identify IM adrenaline as the priority. Fourth, differential diagnosis: distinguishing serotonin syndrome from NMS, or allergic angioedema from hereditary angioedema, is a recurring discriminator. Fifth, pharmacovigilance: candidates are expected to know the Yellow Card scheme, administered by the MHRA, and when reporting is mandatory versus recommended. All healthcare professionals, including doctors in the ED, are encouraged to report suspected ADRs, particularly for newer drugs, serious reactions, and those involving vaccines. For comprehensive, scenario-based preparation across all these domains, the EM Learning Centre homepage provides access to structured question banks and curriculum-mapped lessons.

Revision Pearls: High-Yield Facts for FRCEM SBA Preparation

1. Type A reactions (augmented, dose-dependent) account for approximately 80% of all ADRs. They are predictable and often manageable with dose adjustment rather than complete drug withdrawal.
2. IM adrenaline into the anterolateral thigh is the first-line treatment for anaphylaxis. The dose in adults is 0.5 mg (0.5 mL of 1:1000). IV adrenaline is reserved for cardiac arrest or for those with established IV access under direct anaesthetic monitoring.
3. ACE inhibitor angioedema is bradykinin-mediated, not histamine-mediated. Adrenaline, antihistamines, and corticosteroids are not effective. The ACE inhibitor must be permanently stopped. ARBs carry a small cross-reactivity risk and should be introduced cautiously if an alternative renin-angiotensin agent is required.
4. Serotonin syndrome onset is within hours of a serotonergic drug change or combination. NMS onset is over one to three days following antipsychotic use. Clonus and hyperreflexia favour serotonin syndrome; lead-pipe rigidity favours NMS.
5. Narrow therapeutic index drugs (warfarin, lithium, digoxin, phenytoin, methotrexate, aminoglycosides) are the most common source of FRCEM SBA toxicology stems because small concentration changes produce significant clinical effects.
6. Serum tryptase should be taken at onset (15 to 60 minutes), at one to two hours, and at 24 hours following suspected anaphylaxis. A raised acute tryptase with a normal 24-hour level strongly supports mast cell activation.
7. The UK Yellow Card scheme is run by the MHRA. Any healthcare professional or patient can report a suspected ADR. All new drugs (black triangle products) and serious or unexpected reactions should always be reported regardless of established knowledge of the drug.

Common Pitfalls: Where Candidates Lose Marks

• Selecting antihistamine or corticosteroid as the first-line treatment for anaphylaxis rather than IM adrenaline.
• Treating ACE inhibitor angioedema with adrenaline and antihistamines and failing to identify the bradykinin mechanism.
• Confusing serotonin syndrome with NMS, particularly when both involve hyperthermia and altered consciousness; the neuromuscular examination findings are the key discriminator.
• Failing to document a drug allergy or ADR alert after a confirmed reaction, which is a patient safety and GMC Good Medical Practice obligation.
• Overlooking the need for a minimum six-hour observation period after anaphylaxis treated with adrenaline, due to biphasic reaction risk.
• Assuming that a reaction occurring years after starting an ACE inhibitor cannot be drug-related; ACE inhibitor angioedema can present at any point during treatment.
• Forgetting that Type B reactions require permanent discontinuation and specialist allergy follow-up, not just dose reduction.

How EM Learning Centre Supports Your FRCEM Single Best Answer Revision

Adverse drug reactions are a topic where conceptual depth translates directly into examination marks and, more importantly, into safer clinical practice. The FRCEM SBA practice questions on this platform are written to the standard of the actual examination, with detailed explanatory notes for every answer option. The FRCEM Single Best Answer revision course at EM Learning Centre includes dedicated lessons on Acute Allergy, Anaphylactoid Reactions, Angioedema in the Emergency Department, Hereditary Angioedema in the Emergency Department, and Urticaria in the Emergency Department, all of which address the clinical and pharmacological material covered in this article. These lessons are mapped to the current RCEM curriculum, written by UK emergency medicine consultants, and designed for efficient, high-yield MRCEM SBA and FRCEM SBA exam preparation. If you are building your revision programme, ADRs should feature early and be revisited in the weeks before your exam, as the breadth of drug classes and clinical presentations means that familiarity alone is insufficient. Structured, explanation-led practice is what converts knowledge into reliable examination performance.

References

1. Pirmohamed M, James S, Meakin S, et al. Adverse drug reactions as cause of admission to hospital: prospective analysis of 18 820 patients. BMJ 2004;329:15. The BMJ
2. Resuscitation Council UK. Anaphylaxis Guidelines 2021. Resuscitation Council UK
3. National Institute for Health and Care Excellence. Drug allergy: diagnosis and management. NICE Guideline CG183. NICE
4. Royal College of Emergency Medicine. RCEM Curriculum and Assessment. Royal College of Emergency Medicine
5. British National Formulary. Adverse drug reactions: guidance and reporting. British National Formulary