Management of paediatric asthma in the UK is directed by the British Thoracic Society (BTS) Guidelines, which recommend a stepwise (one to five) treatment plan. Step three of the management guideline for children aged 5-12 years of age recommends the addition of the preventer inhaled medication, including long-acting β2 agonists such as salmeterol. However, there is a wide variation in response to this medication with approximately one in seven people, with a specific genetic change, found to have an increase in asthma symptoms in association with the use of thisiss medication. A related medicine, formoterol, is used less commonly in children with asthma.