A 35‐year‐old woman has been an inpatient in hospital for 5 days. She is on treatment for severe community‐acquired pneumonia and had 48 hours of intravenous antibiotics which has now been changed to oral. She is clinically improving. As an on‐call doctor you have been asked to assess her because she is febrile. She complains of a red sore arm. You note that she still has a venflon in situ. On examination she has a temperature of 38.2°C, a heart rate of 105 beats/min and an arterial blood pressure of 105/70 mmHg. Her skin is red, tender, swollen and indurated around her venflon site.