If asthma is not controlled, NICE advises offering a leukotriene receptor antagonist (LTRA), whereas BTS/SIGN recommends adding a long-acting beta2 agonist (LABA) to the low dose ICS in a combination inhaler. 

Combination inhalers are recommended as a LABA should not be used without ICS for the treatment of asthma. This is because chronic exposure to LABA can be associated with tolerance and reduced sensitivity to the bronchodilator effects of salbutamol. Both guidelines recognise that adding a LABA to ICS is more beneficial than increasing the ICS dose. The aim is to find the lowest dose of ICS to control symptoms. Adult onset asthma can be more difficult to treat and higher doses of ICS may be needed. 

Treatment response should be assessed after four weeks and if the LTRA or LABA have had no response then they should be stopped. They can be continued if there is benefit but asthma control is inadequate. If the patient has tried a LTRA alongside an ICS, then a LABA should be offered as a LABA/ICS combination inhaler. If they have tried a LABA/ICS inhaler then a LTRA should be offered. In both cases, treatment response should again be assessed after four weeks.