Urticaria + stridor + BP 78/40 minutes after IV antibiotic — this is adrenaline IM now, not antihistamines first.
ABCDE
ADRENALINE 0.5 mg IM (1 mg/mL, 0.5 mL) anterolateral thigh immediately — repeat every 5 min; remove trigger; supine with legs raised; high-flow O₂; 2 large-bore IVs + rapid normal saline.
Recognise: airway (angioedema, stridor), breathing (wheeze), circulation (SBP <90 or >30% drop) compromise ± skin/mucosal signs after a trigger — skin signs absent in 20%
Adrenaline IM NOW: 0.5 mg (0.5 mL of 1 mg/mL) IM into the anterolateral thigh — repeat every 5 minutes if no improvement; this is the ONLY first-line drug
Position + access: lie flat, legs raised (left lateral if pregnant, sit up if severe breathlessness); 2 large-bore IVs; 1–2 L 0.9% saline rapidly — adults can sequester 35% of blood volume in 10 min
Airway threats: stridor/tongue swelling → nebulised adrenaline 5 mg + senior anaesthetist NOW; intubate early — angioedema makes late airways impossible
Adjuncts only AFTER adrenaline: hydrocortisone 200 mg IV + cetirizine 10 mg PO/IV — these do nothing for the acute airway/shock
Refractory: adrenaline infusion 0.05–1 mcg/kg/min with monitoring; on β-blockers → glucagon 1–5 mg IV; observe ≥6–24 h for biphasic reaction
Order set
- Adrenaline 0.5 mg IM anterolateral thigh
- 0.9% saline 1–2 L rapid
- High-flow O₂
- Mast cell tryptase (within 2 h, repeat at 24 h)
- Hydrocortisone 200 mg IV (after adrenaline)
- Cetirizine 10 mg (after adrenaline)
- Nebulised adrenaline 5 mg if stridor
- Adrenaline infusion if refractory
Monitor
- q5 minBP, HR, response to IM adrenaline — redose
- ContinuousSpO₂, cardiac monitor, watch for biphasic reaction
- 2 h + 24 hMast cell tryptase samples
- 6–24 hObservation window before discharge (12–24 h if severe, asthmatic, or needed 2 doses)
Escalate / ICU
- Airway oedema progressing despite adrenaline
- Need for adrenaline infusion
- Biphasic reaction
- Refractory hypotension — ICU
Criteria
AdmitAll who needed adrenaline infusion, 2+ doses, or had airway involvement
ObserveMinimum 6 h from symptom resolution; 12–24 h if severe/asthma/β-blocker
ICURefractory shock, airway compromise, infusion required
DischargeAdrenaline auto-injector ×2 prescribed + technique taught + allergy clinic referral
Never
- Give adrenaline IV bolus in a monitored, non-arrest patient — IM thigh first (IV bolus = arrhythmia/infarction)
- Treat with antihistamines or steroids while delaying adrenaline
- Discharge early or without an adrenaline auto-injector and allergy referral
Key
- IM anterolateral thigh — fastest absorption, safest route; no maximum cumulative dose in true anaphylaxis
- Glucagon 1–5 mg IV for patients on β-blockers with refractory anaphylaxis
- Biphasic reactions occur in up to 20% — observation is treatment
Clinical detail — differentials, red flags, pitfalls, disposition
Red flags
- Hoarseness, tongue or lip swelling
- Stridor or silent chest
- SBP <90 or collapse
- Trigger was parenteral (IV drug, sting) — faster and deadlier
Differentials
- Vasovagal syncope (bradycardia, no skin signs)
- ACE-inhibitor angioedema (no urticaria, bradykinin — adrenaline less effective)
- Scombroid poisoning
- Panic attack / globus
Common mistakes
- Walking the patient to resus — lay them flat immediately
- Underdosing adrenaline in adults (0.3 mg is paediatric thinking)
- Relying on steroids to 'prevent' biphasic reactions
- No auto-injector training before discharge
Disposition & follow-up
Discharge with 2 adrenaline auto-injectors, written action plan, trigger avoidance advice, and allergy/immunology referral for testing in 4–6 weeks.
Discharge package
MedicationsAdrenaline auto-injector ×2 (e.g., 0.3 mg) — demonstrate technique; teach second dose into the opposite leg if symptoms persist/recur (RCUK 2025 first-aid update; adrenaline nasal spray is an emerging option); short course of antihistamine
Follow-upAllergy clinic in 4–6 wk for skin/specific-IgE testing; MedicAlert bracelet
Warning symptomsAny lip/tongue tingling, widespread hives, breathing difficulty — use auto-injector immediately and call emergency services
LifestyleTrigger avoidance plan; check drug allergies before every new prescription
💊 Treatment detail — doses & preparation
Adrenaline IM (anaphylaxis)first-line anaphylaxis
Dose0.5 mg IM anterolateral thigh, repeat q5 min PRN
Preparation0.5 mL of 1:1,000 (1 mg/mL) drawn from 1 mg ampoule; no dilution needed
MonitorResponse within 5 min; have IV access + fluids ready
0.9% Sodium chloridecrystalloid
DoseBolus 500 mL over 15–30 min, reassess; maintenance 1–1.5 mL/kg/h
Preparation500/1000 mL bags; add KCl only after urine output confirmed
MonitorHyperchloraemic acidosis with large volumes — prefer balanced (LR) for resuscitation
Adrenaline infusionvasopressor/inotrope
Dose0.05–1 mcg/kg/min IV infusion, titrate to effect
Preparation4 mg in 250 mL D5W/NS (16 mcg/mL) via pump; central access for prolonged use
MonitorTachycardia, arrhythmia, lactate rise; invasive MAP
Hydrocortisone IVglucocorticoid
DoseAdrenal crisis: 100 mg IV bolus then 200 mg/24 h (50 mg q6h or infusion). Septic shock: 50 mg IV q6h
Preparation100 mg vial reconstitute with 2 mL water; bolus over 30 s–10 min
MonitorGlucose, Na⁺, BP response; taper when trigger resolves
Cetirizineantihistamine
Dose10 mg PO/IV OD (anaphylaxis adjunct AFTER adrenaline)
Preparation10 mg tablets
MonitorSedation minimal; adjunct only — never a substitute for adrenaline
Glucagonβ-blocker/CCB antidote
Dose1–5 mg IV bolus (anaphylaxis on β-blockers, β-blocker OD); may repeat/infuse 1–5 mg/h
Preparation1 mg kit reconstitute with supplied diluent
MonitorGlucose (hyper then hypo), vomiting; transient effect
📖 Resuscitation Council UK anaphylaxis guideline + textbook Ch.5Reviewed July 2026