Inhaled corticosteroids (ICS) are anti-inflammatory drugs used primarily in treating persistent asthma and providing long-term maintenance. They target the bronchial mucosa, the lining of the airways, to control inflammation, a critical factor in asthma progression and exacerbation.

ICS work through a multifaceted mechanism of action. They suppress the inflammatory response caused by the proliferation of T_H cells. They also reduce the transcription of the IL-2 gene, which is involved in the immune system's response to pathogens. Finally, ICS decrease the formation of proinflammatory cytokines.

Additionally, ICS inhibit the generation of vasodilators, substances that widen blood vessels, and reduce the release of mediators from eosinophils, another type of immune cell contributing to inflammation.

Several compounds are used in ICS therapy, including beclometasone, budesonide, fluticasone, mometasone, and ciclesonide. These drugs prevent the progression of chronic asthma and can also be effective in managing acute severe cases. They are the FDA-indicated treatment of choice in preventing asthma symptoms in patients with persistent asthma.

ICS are typically administered via inhalers, allowing targeted drug delivery directly to the airways. Spacers are attachments for metered-dose inhalers that can further improve drug delivery by ensuring that more medication reaches the lungs and less is deposited in the mouth and throat.

Despite their benefits, ICS can cause some adverse effects. These may include oropharyngeal candidiasis (thrush), sore throat, croaky voice, and adrenal suppression with high doses. The risk of thrush can be decreased by rinsing the mouth after inhalation to remove residual medication. To minimize other adverse effects, patients should use the lowest effective dose of ICS and ensure proper inhalation technique to reduce medication deposition in the throat.

Despite these potential side effects, ICS can significantly improve asthma symptoms and quality of life. For those with severe asthma, ICS may even eliminate the need for oral glucocorticoids associated with more systemic side effects. ICS remains a cornerstone of asthma management due to its efficacy and relative safety profile.