Inhaled
corticosteroids (ICS) are the most effective controllers of
asthma. They suppress
inflammation mainly by switching off multiple activated inflammatory genes through reversing
histone acetylation via the recruitment of
histone deacetylase 2 (HDAC2). Through suppression of airway
inflammation ICS reduce
airway hyperresponsiveness and control
asthma symptoms. ICS are now first-line
therapy for all patients with persistent
asthma, controlling
asthma symptoms and preventing exacerbations. Inhaled long-acting β₂-agonists added to ICS further improve
asthma control and are commonly given as combination
inhalers, which improve compliance and control
asthma at lower doses of
corticosteroids. By contrast, ICS provide much less clinical benefit in
COPD and the
inflammation is resistant to the action of
corticosteroids. This appears to be due to a reduction in HDAC2 activity and expression as a result of oxidative stress. ICS are added to
bronchodilators in patients with severe
COPD to reduce exacerbations. ICS, which are absorbed from the lungs into the systemic circulation, have negligible systemic side effects at the doses most patients require, although the high doses used in
COPD has some systemic side effects and increases the risk of developing
pneumonia.