A 34-year-old woman collapses 5 minutes after a wasp sting. She has stridor, a blood pressure of 78/40 mmHg and widespread urticaria. Which is the immediate treatment of choice?

Answer and explanation

Correct answer: B. Intramuscular adrenaline 500 micrograms as 0.5 mL of 1 in 1000 into the anterolateral thigh

  1. Step 1: Stridor, hypotension and urticaria after a trigger make this anaphylaxis with airway and circulation compromise.
  2. Step 2: Resuscitation Council UK advises IM adrenaline 1 in 1000 as first-line; the adult dose is 500 micrograms (0.5 mL) in the anterolateral thigh.
Answer
Intramuscular adrenaline 500 micrograms as 0.5 mL of 1 in 1000 into the anterolateral thigh.
Why not the others: Intramuscular adrenaline 300 micrograms as 0.3 mL of 1 in 1000 into the deltoid with oxygen: 300 micrograms is the dose for a child aged 6 to 12 years, which under-doses an adult. Intravenous adrenaline 500 micrograms as 5 mL of 1 in 10 000 through a peripheral cannula in the resuscitation bay: IV adrenaline outside specialist use risks arrhythmia and is reserved for experienced clinicians using an infusion. Intravenous chlorphenamine 10 mg followed by observation for ten minutes before any further drug is given: Antihistamines are second-line and do not treat airway or circulatory compromise, so delaying adrenaline is dangerous.

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