Inhaled corticosteroids are drugs used to manage both mild and severe asthma symptoms. Higher doses are used to treat severe attacks. In this article, we will discuss what corticosteroids are and how they are used to treat acute asthma exacerbations.

Corticosteroids are prescribed in almost every branch of medicine, including in the treatment of inflammatory bowel disorders, contact dermatitis, and osteoarthritis. Inhaled corticosteroids are usually prescribed for regular use in almost all cases of asthma, as they reduce the likelihood of disease progression. Their ubiquitous use in medicine is evidence of their effectiveness. However, they are not without drawbacks. High doses, in the short-term for acute asthma exacerbations or cumulatively over the course of long-term asthma management, are associated with adverse effects such as pneumonia, oral thrush, and voice disorders. 

The pathophysiology of asthma, the use of inhaled corticosteroids in asthma treatment, and the justification of inhaled corticosteroid use, despite its drawbacks, will be explored in this article.

Pathophysiology of Asthma and Acute Exacerbations

Asthma is a chronic inflammatory airway disorder. Asthma treatments aim to reduce the inflammation which obstructs the airways. People with asthma suffer from episodes of chest tightness, wheezing, breathlessness, and coughing, as a result of the airway obstructions.¹ Episodes can cause disturbances to sleep, as they often occur in the early morning or late evening.

The exact causes of asthma are unclear - it seems that environmental and genetic factors all play a part in asthma development.^1,2 Some obstructions in the airway seem to be linked to vagus nerve activity. Neurotransmitters are released which activate smooth muscle in the bronchioles to contract and cause mucus glands to secrete mucus, working in conjunction to form obstructions.³ These obstructions are largely reversible with the use of bronchodilators, which can reverse airway contraction by stimulating smooth muscle relaxation.^2,3 In most patients, bronchodilators are used in conjunction with inhaled corticosteroids - another type of drug which can reduce inflammation and ease obstructions.

Attacks can occur without any noticeable stimulus, but common identifiable triggers include respiratory infections, pollution, and allergens, which worsen inflammation in the airways, creating greater obstruction and more severe attacks.⁹ These triggers create seasonal rises in acute asthma exacerbations, following patterns of increased respiratory infection spread in the autumn, and rise of hayfever symptoms in late spring.²  Inflammation associated with increased levels of immune factors is known as Type 2 inflammation, and requires an adjustment in medication in order to avoid further exacerbation. 

An increase in inflammation often doesn’t present itself with worse symptoms immediately. This means inflammation can become more severe without patients noticing. Many patients don’t fully comply with treatment plans because of this.² This can lead to seemingly sudden exacerbations - an increase in the severity of symptoms, also referred to as a flare-up. An acute exacerbation is defined by requiring at least three days of corticosteroid treatment, or any emergency hospital visit where corticosteroids were administered.²  

Role of Corticosteroids in Asthma Treatment

Corticosteroids are a commonly prescribed class of anti-inflammatory steroids. They are used to treat several diseases, including hayfever, atopic eczema, and inflammatory bowel diseases like ulcerative colitis.⁷ The drug can be taken in several forms depending on the condition. This includes as an injection, topical cream, suppository, tablet, or through an inhaler.

Inhaled corticosteroids (ICS) are prescribed in most mild and moderate cases of asthma alongside a bronchodilator, as combined use has been found to be more effective in avoiding exacerbations than either used alone.²  ICS are inhaled and partly absorbed through the lungs (around 10-40% of the drug), with the remainder passing through the gastrointestinal tract and mostly inactivated in the liver.¹² The small amount which remains bioactive will be distributed around the body, with some acting in the circulatory system, similarly to how an oral corticosteroid (OCS) would function.¹² The exact mechanism of action by which ICS abate inflammation is unclear.⁴

Long-term ICS use and compliance is important for asthma control and abating exacerbation. Studies show that correct usage of prescribed ICS during the early stage of respiratory illness reduces the likelihood of an acute exacerbation. There is also some evidence that use of ICS in the early stage of asthma diagnosis reduces the likelihood of further asthma progression.⁵

As mentioned, corticosteroids can also be prescribed orally as a pill. This is the most powerful method of taking a steroid and affects the entire body, rather than one localised area. For acute asthma exacerbations, OCS are currently preferred for treating Type 2 inflammation, although some studies suggest that using ICS in conjunction with OCS might be more effective.⁴ Typically, OCS is used only in severe cases, such as when an episode requires urgent medical attention. The current guidelines for asthma treatment are described in the next section.

Guidelines for use of Inhaled Corticosteroids in Asthma

GINA (Global Initiative for Asthma) releases annual guidelines for treating asthma as part of their efforts to improve asthma treatments worldwide. The following section will summarise the guidelines released in 2023. More up to date information can be found from GINA’s homepage.

Very mild cases of asthma (defined as fewer than two attacks per month) can be treated with a bronchodilator for symptom relief.⁶ Any case of asthma more severe than this should be treated with a dual treatment of a bronchodilator for immediate symptom relief alongside a regular low-dose ICS.⁵ This is because although bronchodilators can provide immediate symptom relief, they do not reduce the risk of flare-ups. Low-dose ICS has been found to halve the risk of asthma-related death as well as reducing likelihood of exacerbation.⁹

Patients whose asthma symptoms do not come under control at low doses of ICS can be gradually prescribed greater doses. Before this, it must be ensured that patients are correctly administering and complying with their treatment plans - noncompliance is a common issue, and can in fact increase the likelihood of exacerbations.⁵ Severe asthma is diagnosed if the condition has not stabilised after 3-6 months of consistent treatment.⁶ The specific phenotype of severe asthma must be determined in order to guide further ICS prescription. A combination of blood tests, chest scans, and bone density scans should be undertaken to determine the level of Type 2 inflammation present.

In patients with mild or moderate asthma, Type 2 inflammation will abate in response to regular low-dose ICS. However, some patients diagnosed with severe asthma may require much higher doses or possibly OCS to abate Type 2 inflammation. For this asthmatic phenotype, often another treatment will be recommended or designed to accompany a high dose ICS. This is because even short-term use of OCS is associated with severe side-effects, such as psychiatric disorders and diabetes.⁴ 

The 2023 GINA Severe Asthma Treatment Guide provides a handy flowchart from initial asthma diagnosis to determination of severe asthma phenotype, and includes the myriad of treatment options applicable to each stage, in more depth than described here.

Potential Risks and Side Effects of Inhaled Corticosteroids

Corticosteroids have numerous side effects, which vary depending on the form of the medication, size of dose, and the patient’s own tolerance to the drug. High doses, or a high cumulative dose over time, can result in diabetes, associated with weight gain, and osteoporosis, among many other issues.⁴ These are more severe adverse side effects and are more likely with the use of both short or long-term OCS, where the corticosteroid dose is high and has a widespread effect on the body.¹¹

In comparison, ICS have a much better safety profile.¹² At the range of doses usually provided for regular asthma symptom control, mild side effects include throat irritation, and fungal infections such as oral candidiasis, which can be avoided by proper inhaler apparatus use or the use of a spacer (for children). That is not to suggest that ICS are completely safe: severe symptoms are uncommon, but include cataract development, glaucoma, and skin atrophy.¹²

There is also some evidence that growth retardation can occur in young populations as a result of corticosteroid use. However, the evidence is unclear and given that regular ICS and bronchodilator treatment reduces the likelihood of acute asthma exacerbations in children aged between 6-12 years old by 25%, the importance of controlling asthma symptoms currently outweighs the low risk of growth retardation.^5,12

This is generally the medical perspective on corticosteroids, particularly in treating asthma - despite its side effects, ICS provide both long-term symptom relief and abate future severe exacerbations which can massively diminish the quality of life of patients, and the positive results of their controlled use far outweigh the low likelihood of severe side-effects. This perspective is similarly held by asthma patients who have properly discussed their treatment plans with healthcare professionals and undergone corticosteroid therapy. Further emphasis must be placed on ensuring patients understand the risks of corticosteroid therapy, how corticosteroids function, and how they can improve patient’s health in order to ensure treatment compliance and patient confidence.^6,10,13 Some side effects can be avoided by providing patients with a holistic education on how to administer the ICS.

Summary

Inhaled corticosteroids are the mainstay of asthma treatment, acting to reduce disease progression by reducing further inflammation of the airways. They are generally well-tolerated, with low dose ICS being associated with minor side effects such as throat irritation. High doses are associated with more severe adverse effects, such as cataract development and glaucoma. Minor side effects can generally be avoided with proper instruction on using inhaler pumps. Severe side effects can worry patients and their family, however, the benefits of ICS treatment far outweigh the low likelihood of side effects. Patients should be provided with a holistic education in how corticosteroids work and the importance of their role in abating further inflammation and acute asthma exacerbations.

Frequently Asked Questions

What is a corticosteroid?

Corticosteroids are a commonly prescribed class of anti-inflammatory steroids. They are used to treat several diseases, including hayfever, atopic eczema, and inflammatory bowel diseases, like ulcerative colitis.⁷ The drug can be taken in several forms depending on the condition. This includes as an injection, topical cream, suppository, tablet, or through an inhaler.

What side effects are associated with inhaled corticosteroids?

Mild side effects include throat irritation and fungal infections such as oral candidiasis, which can be avoided by proper inhaler apparatus use or the use of a spacer (for children). Severe symptoms are uncommon but include cataract development, glaucoma, and skin atrophy.¹²

What is an acute asthma exacerbation?

An increase in inflammation in the airways leading to seemingly sudden exacerbations - an increase in the severity of symptoms, also referred to as a flare-up. An acute exacerbation is defined by requiring at least three days of corticosteroid treatment, or any emergency hospital visit where corticosteroids were administered.²