Mark, a 29-year-old electrician presents to his GP with six episodes of cough, wheeze, yellow sputum and abdominal bloating over the past four months. He has had asthma since the age of eight, which has previously been controlled well with inhaled budesonide/formoterol 200/6 bd. He has no other known medical comorbidities and does not drink alcohol or smoke.

At initial presentation the clinical findings are consistent with an infective exacerbation of asthma, so Mark is prescribed antibiotics, a three-day course of prednisolone 50mg and an increased dose of budesonide/formoterol 400/12 bd.