Anaphylaxis after a first dose of antibiotic

PLAB 2 & PRES 3 · emergency medicine / allergy · hard · 10 minutes

Candidate brief

You are an FY2 doctor on a respiratory ward. Mr Tomasz Nowak, 46, was admitted this morning with community-acquired pneumonia. His first dose of intravenous co-amoxiclav was started 10 minutes ago. The nurse has just pressed the buzzer and called you in urgently: he has become itchy and flushed, his lips are swelling, and he is wheezing. Observations now: respiratory rate 28/min, SpO2 91% on air, BP 88/52 mmHg, pulse 122/min, temperature 36.9 °C. He is alert but frightened. His drug chart records no known drug allergies. Please assess and manage this patient.

What examiners look for

Anaphylaxis is a clinical diagnosis made in seconds from a pattern — exposure, then airway, breathing or circulation compromise, usually with skin signs. The candidate who waits for certainty, a blood test or a senior has misunderstood the disease: the treatment window is the diagnosis. Adrenaline IM is the treatment, and everything else is an extra. 500 micrograms into the anterolateral thigh, early, repeated at five minutes if needed. Antihistamines do not open airways or raise blood pressure; steroids act over hours. In audits of anaphylaxis deaths, delayed adrenaline is the recurring theme — this station is built so that delay visibly deteriorates the patient. Stop the trigger and keep the line. The infusion comes down first; the cannula stays — you will need it for fluids, and ripping out access in a crashing patient is a self-inflicted wound. Positioning is a genuine dilemma scored both ways: flat with legs up for the circulation, sat up for the breathing — and catastrophic if he stands. State the compromise and the reasoning, and keep adjusting as one system wins. Prior tolerance proves nothing. He had amoxicillin twice without trouble, which is exactly how sensitisation works. Candidates who let "he's had it before" talk them out of the diagnosis repeat the most documented reasoning error in allergy practice. Improvement is the middle of the station, not the end. Biphasic reactions return unannounced, so observation, tryptase timing, allergy documentation that the next prescriber cannot miss, an alternative antibiotic plan, and specialist referral are the difference between surviving the scenario and passing the station. Talk while you treat. In anaphylaxis the patient is conscious, terrified and fighting for air; short, factual, confident sentences ("this injection will help your breathing") are a clinical intervention that keeps the airway you are trying to save.

Guideline references

Practise this station

Role-play it with an AI patient and get feedback against the full marking scheme. Create a free account — 3 stations per month free.