Why this matters for EMT students: Allergic and immune-mediated reactions can progress from an itchy rash to airway obstruction and distributive shock within minutes. Poisoning emergencies may look similar to allergy—wheeze, collapse, vomiting, altered consciousness or seizures—but require a different antidote and transport plan. The EMT’s value is early recognition, correct first actions, prevention of further exposure, repeated ABCDE assessment and precise handover.
Safety notice: This is an educational guide. Use the current Uganda Clinical Guidelines, local emergency drug concentrations, poison-centre advice and medical direction. Never delay airway, breathing and circulation support while searching for a named antidote. Antidotes are adjuncts; many patients need oxygen, ventilation, fluids, ECG monitoring, glucose correction, seizure control and critical care.
Learning outcomes
- Differentiate allergy, intolerance, anaphylaxis, angioedema and non-immune hypersensitivity.
- Explain the four Gell–Coombs hypersensitivity mechanisms and their clinical examples.
- Recognise life-threatening airway, breathing and circulation features and start an anaphylaxis response promptly.
- Identify severe cutaneous adverse reactions, serum sickness and drug-induced organ injury that need urgent referral.
- Match common poisoning patterns with antidotes while understanding indications, limitations, interactions and monitoring.
- Document exposures, timing, treatment and response so the receiving team can continue care safely.
1. Key terms
| Term | Meaning and emergency relevance |
|---|---|
| Allergy | An immune-mediated reaction to an otherwise harmless antigen; symptoms can be mild, severe or delayed. |
| Hypersensitivity | An exaggerated or inappropriate immune response that causes tissue injury. It includes allergic and non-allergic mechanisms. |
| Intolerance | An unpleasant reaction that is not immune-mediated, such as nausea from an opioid or flushing from niacin. |
| Anaphylaxis | A rapid, potentially fatal systemic reaction with airway, breathing or circulation compromise, usually with skin/mucosal features but sometimes without them. |
| Angioedema | Deeper swelling of skin, lips, tongue, larynx or bowel. It may be histamine-mediated or bradykinin-mediated and can obstruct the airway. |
| Antidote | A medicine or intervention that prevents, binds, neutralises or reverses a specific toxin effect. It never replaces resuscitation and observation. |
2. Gell–Coombs hypersensitivity types
| Type | Mechanism | Examples | Time course |
|---|---|---|---|
| I — immediate | IgE activates mast cells and basophils; histamine, tryptase, leukotrienes and other mediators are released. | Anaphylaxis, allergic asthma, urticaria, food allergy, latex reaction. | Seconds to minutes; can be biphasic. |
| II — antibody-mediated cytotoxic | IgG/IgM bind cell or tissue antigens, activating complement or cellular destruction. | Haemolytic transfusion reaction, autoimmune haemolytic anaemia, some drug-induced cytopenias. | Hours to days. |
| III — immune-complex | Circulating antigen–antibody complexes deposit in tissues and activate complement. | Serum sickness, some vasculitides, post-infectious inflammation. | Days to weeks. |
| IV — delayed T-cell | Sensitised T cells release cytokines or directly injure cells; no antibody is required. | Contact dermatitis, tuberculin reaction, severe cutaneous drug reactions. | Usually 48–72 hours or longer. |
Clinical caution: A previous mild reaction does not guarantee the next reaction will be mild. Conversely, a rash alone does not prove anaphylaxis. Grade the current airway, breathing and circulation every time.
3. Common triggers in Ugandan emergency practice
- Medicines: beta-lactam antibiotics, sulfonamides, NSAIDs, anticonvulsants, opioids, anaesthetic agents, vaccines and biologics.
- Foods: groundnuts, nuts, milk, eggs, fish, shellfish, fruits and hidden ingredients.
- Venom and bites: bees, wasps, ants, snakes and other arthropods.
- Latex and occupational exposures: gloves, catheters, tourniquets and equipment.
- Contrast and blood products: immediate reactions, delayed rashes or haemolysis.
- Non-immune mimics: radiocontrast reactions, exercise, heat, alcohol, opioids or direct mast-cell activation.
4. Recognising anaphylaxis
Think anaphylaxis when illness begins suddenly after a plausible exposure and there is airway, breathing or circulation compromise, usually with skin or mucosal change. Skin signs can be absent, especially in severe shock. Gastrointestinal symptoms may be prominent after food exposure.
| System | Findings | Danger sign |
|---|---|---|
| Airway | Throat tightness, hoarse voice, tongue/lip swelling, stridor, drooling, difficulty swallowing. | Rapidly worsening voice, stridor, inability to speak or maintain secretions. |
| Breathing | Wheeze, cough, chest tightness, tachypnoea, hypoxia, cyanosis or silent chest. | Severe bronchospasm, exhaustion, falling SpO2 or respiratory arrest. |
| Circulation | Dizziness, collapse, tachycardia, hypotension, pallor, clammy skin, weak pulse. | Shock, altered consciousness or cardiac arrest. |
| Skin/mucosa | Flushing, itching, urticaria, erythema, angioedema. | Do not wait for a rash before treating airway/breathing/circulation compromise. |
| Gastrointestinal | Cramping, vomiting or diarrhoea, especially after food exposure. | Persistent vomiting with shock or airway swelling. |
5. Emergency treatment of anaphylaxis
- Call for help and stop the trigger: stop an infusion or remove a visible stinger if safe; do not delay treatment while looking for the trigger.
- Position correctly: lay flat with legs raised if shock is present. Allow a breathless patient to sit with legs outstretched, but never allow a shocked patient to stand or walk. Place an unconscious breathing patient in the recovery position.
- Give IM adrenaline/epinephrine immediately into the outer mid-thigh using the concentration and age/weight protocol available locally. Adrenaline is first-line for airway, breathing or circulation problems. Do not substitute an antihistamine or steroid.
- Reassess after about five minutes: repeat IM adrenaline if airway, breathing or circulation problems persist, according to protocol. Record time and dose.
- Support ABCDE: high-concentration oxygen when indicated, airway equipment and suction ready, IV/IO access by trained personnel, rapid crystalloid for persistent shock and continuous monitoring.
- Treat bronchospasm or upper-airway obstruction: nebulised bronchodilator or nebulised adrenaline may be added by protocol; these never replace IM adrenaline. Prepare early for advanced airway management.
- Transport and observe: all anaphylaxis patients require medical assessment because symptoms can recur after initial improvement. Observation time depends on severity, treatment and local guidance.
Adrenaline safety: Use the correct concentration and route. A 1 mg/mL (1:1000) preparation is used for IM anaphylaxis in many protocols; IV adrenaline is a specialist treatment for refractory shock or cardiac arrest and can cause fatal dosing errors. Always read the ampoule and follow local policy.
What not to do
- Do not wait for rash, wheeze or a blood-pressure reading if the patient has sudden airway or breathing compromise after exposure.
- Do not give antihistamine first while delaying adrenaline; antihistamines mainly improve itch and hives, not shock or airway oedema.
- Do not use routine corticosteroids as a substitute for adrenaline; their onset is too slow to reverse acute airway or circulatory collapse.
- Do not make a shocked patient stand, walk or sit upright suddenly.
- Do not leave the patient alone after apparent recovery; biphasic reactions can occur.
6. Differential diagnosis of sudden collapse or wheeze
| Look-alike | Clues | Important distinction |
|---|---|---|
| Severe asthma | Wheeze, chest tightness, previous asthma, no urticaria or trigger in some cases. | Asthma and anaphylaxis can coexist; treat suspected anaphylaxis with adrenaline and protocol-led bronchodilator. |
| Vasovagal syncope | Brief faint after pain/needle, pallor, bradycardia, rapid recovery when supine. | Persistent hypotension, wheeze, swelling or urticaria favours anaphylaxis. |
| Panic attack | Hyperventilation, fear, tingling, normal oxygenation and circulation. | Never label before checking ABCDE, glucose and exposure history. |
| Hereditary/bradykinin angioedema | Recurrent non-itchy swelling, abdominal pain, family history; often no urticaria. | Adrenaline may be less effective; airway planning and specialist therapy are urgent. |
| Sepsis or toxin | Fever, altered mental state, hypotension, exposure, abnormal glucose or pupils. | Continue resuscitation and source/toxin assessment; do not assume an allergy. |
7. Angioedema and airway planning
Swelling of the tongue, floor of mouth or larynx can progress quickly. Ask about voice change, drooling, dysphagia, stridor and previous episodes. Sit the patient only if breathing requires it; prepare suction, oxygen and advanced airway support early. Histamine-mediated angioedema may accompany urticaria and respond to anaphylaxis treatment. Bradykinin-mediated angioedema, including ACE-inhibitor reactions, often lacks itch or hives and needs urgent airway and specialist management.
8. Severe cutaneous adverse reactions
| Condition | Typical features | EMT priorities |
|---|---|---|
| Urticaria | Transient itchy wheals that move or fade; no mucosal injury. | Check for progression to anaphylaxis; document trigger and medicine exposure. |
| Serum sickness-like reaction | Fever, urticarial/morbilliform rash, joint pain, lymphadenopathy days after a medicine or infection. | Stop suspected medicine only with clinical direction, assess organ involvement and refer. |
| DRESS | Drug reaction with eosinophilia and systemic symptoms: fever, facial oedema, widespread rash, lymphadenopathy and liver/kidney injury. | Urgent hospital assessment; ask about anticonvulsants, antibiotics and all new medicines. |
| SJS/TEN | Painful dusky rash, bullae, epidermal detachment, mucosal erosions, fever and systemic illness. | Medical emergency: stop suspected drug under clinician direction, protect skin/eyes/airway, fluid/temperature support and urgent specialist care. |
| Fixed drug eruption | One or more sharply demarcated lesions recur at the same site after re-exposure. | Record the medicine and advise specialist review; extensive blistering needs emergency care. |
9. Drug-allergy history that prevents harm
- What exact medicine, formulation, route and dose caused the reaction?
- How long after the dose did symptoms begin?
- What symptoms occurred—itch, hives, swelling, wheeze, fainting, fever, blistering or organ injury?
- Was the medicine stopped, and what treatment was required (adrenaline, ventilation, admission, ICU)?
- Has the person tolerated related medicines since then?
- Record a specific reaction, not just “allergy.” “Amoxicillin—anaphylaxis with wheeze and hypotension in 2024” is safer than “penicillin allergy.”
10. Antidote principles
- Resuscitate first: airway, breathing, circulation, disability, exposure, glucose, temperature and ECG come before a named antidote.
- Identify the toxin: agent, formulation, amount, route, time, co-ingestions, patient weight, pregnancy and kidney/liver disease.
- Use a poison-centre or senior consultation: antidotes have indications, contraindications, dose limits and monitoring requirements.
- Anticipate delayed toxicity: modified-release tablets, long half-life drugs, fat-soluble toxins and recurrent opioid respiratory depression can outlast early improvement.
- Bring evidence: packets, bottles, photographs, pesticide labels and medication lists can be life-saving.
- Document the response: time, route, dose, vital signs before/after, adverse reactions and the reason for repeating or stopping therapy.
11. High-yield antidotes for EMT revision
| Toxin/clinical problem | Antidote or targeted treatment | Key cautions and monitoring |
|---|---|---|
| Opioids | Naloxone, titrated to restore adequate breathing rather than complete alertness. | Shorter duration than many opioids; recurrent respiratory depression, pulmonary oedema, pain and precipitated withdrawal. Continue ventilation and observation. |
| Paracetamol/acetaminophen | N-acetylcysteine (NAC) according to time, concentration and liver-risk protocol. | Do not wait for symptoms; an apparently well patient may develop delayed hepatic failure. Anaphylactoid reactions can occur during IV NAC. |
| Benzodiazepines | Flumazenil only in carefully selected cases with expert advice. | Can precipitate seizures, withdrawal and dysrhythmias in mixed overdose or dependence; airway support is usually safer. |
| Tricyclic antidepressants / sodium-channel blockade | Sodium bicarbonate under toxicology protocol. | Indicated for QRS widening, hypotension or ventricular dysrhythmia in appropriate poisonings; monitor pH, sodium, potassium and fluid status. |
| Organophosphate/carbamate cholinergic poisoning | Atropine; pralidoxime may be indicated for organophosphates. | Use PPE and decontamination. Titrate atropine to drying of bronchial secretions and improved ventilation, not pupil size alone; watch for delirium/hyperthermia. |
| Beta-blocker toxicity | Glucagon, high-dose insulin euglycaemic therapy, vasopressors and other specialist measures. | Bradycardia and shock may be profound; monitor glucose, potassium, ECG and fluid status continuously. |
| Calcium-channel blocker toxicity | IV calcium, high-dose insulin euglycaemic therapy, vasopressors and specialist support. | Hyperglycaemia, hypoglycaemia, hypokalaemia and myocardial dysfunction require serial monitoring. |
| Digoxin toxicity | Digoxin-specific antibody fragments (digoxin-Fab) when severe or indicated. | Arrhythmias and potassium shifts; do not delay specialist advice for a single level if unstable. |
| Warfarin | Vitamin K; four-factor PCC for life-threatening bleeding per protocol. | Balance thrombosis and bleeding risk; document INR, bleeding site and time of last dose. |
| Heparin | Protamine in selected significant bleeding. | Can cause hypotension/anaphylaxis and has dose limitations; resuscitation and surgical control may still be needed. |
| Methemoglobinaemia | Methylene blue when indicated; specialist consultation is essential. | Pulse oximetry may be misleading; risk of serotonin syndrome and haemolysis in G6PD deficiency. |
| Cyanide/smoke inhalation | Hydroxocobalamin and advanced supportive care per hazardous-exposure protocol. | Scene safety, decontamination and oxygenation; hydroxocobalamin causes red discoloration and can interfere with some tests. |
| Methanol/ethylene glycol | Fomepizole (or protocol-specific alternative), correction of acidosis and haemodialysis. | Visual symptoms, high anion/osmolar gap and renal injury may be delayed; urgent toxicology care. |
| Sulfonylurea hypoglycaemia | Dextrose plus octreotide under medical/toxicology direction. | Recurrent hypoglycaemia is common; monitor for many hours, especially with modified-release products. |
| Iron poisoning | Deferoxamine in severe poisoning. | GI symptoms, shock and metabolic acidosis; treatment requires hospital and laboratory monitoring. |
| Local anaesthetic systemic toxicity | 20% lipid emulsion plus airway, seizure and cardiovascular support. | Stop local anaesthetic, call for resuscitation help and follow a lipid-rescue protocol. |
12. Antidotes by toxidrome
| Toxidrome | Pattern | Antidote/targeted support |
|---|---|---|
| Opioid | CNS depression, pinpoint pupils, slow/absent breathing, bradycardia. | Ventilation and naloxone; observe for recurrence. |
| Cholinergic | Salivation, lacrimation, urination, diarrhoea, vomiting, bronchorrhoea, bronchospasm, bradycardia, miosis and fasciculations. | PPE/decontamination, atropine, pralidoxime for organophosphate exposure, airway support. |
| Anticholinergic | Hot, dry skin, mydriasis, urinary retention, ileus, tachycardia, delirium. | Supportive care, temperature/ECG monitoring and specialist advice; avoid dangerous physical restraint. |
| Sympathomimetic | Agitation, sweating, mydriasis, tachycardia, hypertension, hyperthermia, seizures. | Quiet environment, benzodiazepine-led seizure/agitation control and cooling per protocol. |
| Sedative-hypnotic | Ataxia, slurred speech, CNS depression and hypoventilation. | Airway/ventilation and glucose; selective flumazenil only with expert advice. |
| Serotonergic | Agitation, clonus/hyperreflexia, tremor, diarrhoea, diaphoresis, hyperthermia. | Stop triggers, supportive care, cooling and urgent toxicology review. |
13. Decontamination and exposure safety
- Scene safety first: identify fumes, pesticides, contaminated clothing, powders, sharps and secondary exposure. Use gloves, eye protection and respiratory protection as trained.
- Remove from exposure: fresh air for inhalation when safe, remove contaminated clothing and irrigate skin/eyes with copious clean water according to the chemical protocol.
- Never induce vomiting: aspiration, burns and recurrent exposure can worsen injury. Do not give oral fluids or charcoal to a drowsy patient without a protected airway and expert advice.
- Preserve information: keep the product container, photograph the label, estimate amount and record time and route.
- Protect rescuers: a patient contaminated with pesticide or chemical can expose ambulance staff; request hazmat/decontamination support when required.
14. Special populations and antidote safety
| Patient group | Extra considerations |
|---|---|
| Children | Weight-based calculations, accidental ingestion, smaller airway and rapid deterioration. Use paediatric concentrations and double-check arithmetic. |
| Pregnancy | Maternal oxygenation and circulation are priorities; do not withhold life-saving anaphylaxis or antidote treatment. Involve obstetric and toxicology teams. |
| Older adults | Polypharmacy, renal impairment, falls, frailty and atypical presentations. Start from physiology, not the medication list alone. |
| Asthma or cardiac disease | Adrenaline remains first-line for anaphylaxis; monitor rhythm and perfusion closely. Do not withhold it because of comorbidity. |
| Renal/hepatic disease | Longer toxin half-life and altered antidote clearance. Expect delayed toxicity and seek specialist dosing guidance. |
| Communication barriers | Use interpreters, accessible language and family/support persons with consent. Confirm exposure rather than relying on assumptions. |
15. Clinical scenarios
Scenario 1 — Antibiotic reaction: Minutes after IV ceftriaxone, a patient develops hoarseness, wheeze, urticaria and dizziness. Stop the infusion, call for help, lay the patient appropriately, give IM adrenaline using the local concentration/protocol, support oxygenation and prepare transport. An antihistamine alone is inadequate.
Scenario 2 — ACE-inhibitor angioedema: A patient on enalapril has progressive tongue swelling and a muffled voice but no hives. Treat airway compromise as an emergency, give anaphylaxis therapy if clinically indicated, prepare early airway support and tell the receiving team that bradykinin-mediated angioedema is possible.
Scenario 3 — Pesticide exposure: A farm worker is sweating, vomiting, bradycardic, wheezing and has pinpoint pupils after spraying. Keep rescuers safe, remove contaminated clothing, irrigate as indicated, support ventilation and request urgent atropine/pralidoxime-led toxicology management.
Scenario 4 — Unknown tablets: An unconscious person has slow respirations and a packet of codeine plus diazepam. Ventilate, check glucose, administer naloxone when opioid toxicity is suspected and observe. Do not reflexively use flumazenil in a mixed overdose.
Scenario 5 — Paracetamol ingestion: A teenager feels well four hours after swallowing tablets. Do not reassure or discharge from the scene. Record the dose/time, bring the packet, check for co-ingestions and arrange urgent NAC assessment because liver injury can be delayed.
Scenario 6 — Painful blistering rash: A patient started carbamazepine ten days ago and now has fever, mucosal ulcers and skin tenderness. Suspect SJS/TEN, stop further exposure under medical direction, protect airway/skin/eyes and transfer urgently; do not treat as a simple allergy.
16. Handover and documentation template
- Exposure: suspected agent, product/strength, dose estimate, route, time and co-exposures.
- Reaction: first symptom, progression, skin/mucosa, airway, breathing, circulation, neurological findings and temperature.
- Interventions: adrenaline/antidote name, concentration, route, dose, time, oxygen/ventilation, fluids, decontamination and response.
- Measurements: serial vital signs, ECG rhythm/QRS/QTc, glucose, GCS/AVPU, urine output and relevant point-of-care tests.
- Background: allergies, medicines, asthma, heart/kidney/liver disease, pregnancy, previous reactions and baseline function.
- Safety: contamination risk to staff, safeguarding, intentional self-harm, means access and who was informed.
17. Revision questions
- Why is IM adrenaline first-line in anaphylaxis while antihistamines and steroids are adjuncts?
- List four airway or breathing signs that should trigger immediate anaphylaxis treatment.
- How does bradykinin-mediated angioedema differ from histamine-mediated urticaria?
- Why can a patient with severe anaphylaxis have no skin rash?
- When might naloxone need to be repeated after apparent improvement?
- Why is flumazenil hazardous in mixed overdose or benzodiazepine dependence?
- Name three causes of cholinergic toxidrome and two targeted treatments.
- Which antidote is used for significant paracetamol exposure and why should treatment not wait for symptoms?
- What findings suggest SJS/TEN rather than simple urticaria?
- What exposure and treatment details must appear in an antidote handover?
18. Key take-home points
- Adrenaline is the life-saving first-line medicine for anaphylaxis with airway, breathing or circulation problems.
- Position, oxygenation, ventilation, fluids, monitoring and rapid transport are as important as the antidote.
- Antihistamines relieve itch/hives but do not reverse shock or upper-airway obstruction; routine steroids do not replace adrenaline.
- Antidotes are toxin-specific, time-sensitive and potentially harmful; obtain expert advice and monitor the response.
- Always consider mixed poisoning, delayed toxicity, recurrent respiratory depression and secondary contamination.
- Record the exact reaction and suspected medicine so future care is safer and unnecessary “allergy” labels are avoided.
Selected authoritative resources
- Resuscitation Council UK: Emergency treatment of anaphylaxis.
- WHO pharmacovigilance and anaphylaxis resources.
- NHS poisoning first-aid information.
- MSD Manual: drug hypersensitivity and severe reactions.
For EMT practice: When in doubt, return to ABCDE, remove further exposure, call for help, use the correct first-line treatment and keep reassessing. A precise timeline and clean handover can be as valuable as the medicine itself.