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An anti-asthmatic agent, also known as an anti-asthma drug, refers to a drug that can aid in airway smooth muscle dilation to allow normal breathing during an asthma attack or reduce inflammation on the airway to decrease airway resistance for asthma patients, or both. The goal of asthmatic agents is to reduce asthma exacerbation frequencies and related hospital visits.
Anti-asthmatic agents as rescue medications for acute asthma attacks include short-acting β2-adrenergic receptor agonists (SABA), short-acting muscarinic antagonists (SAMA), systemic , and magnesium sulfate. Anti-asthmatic agents as maintenance medications for asthmatic symptom control include long-acting β2-adrenergic receptor agonists (LABA), inhaled glucocorticoids, long-acting muscarinic antagonists (LAMA), /phosphodiesterase inhibitors, antileukotriene, mast cell stabilizers, and certain types of monoclonal antibodies.
Global Initiative of Asthma (GINA) is the official guideline on the usage of anti-asthmatic agents. The GINA guideline outlines the class, dosage, and administration of anti-asthmatic agents prescription depending on the severity of asthma symptoms and nature.
β2-adrenergic agonists can trigger the activation of Gs protein-coupled β2-adrenergic receptors on the airway smooth muscle cells in the lungs. The β2-adrenergic receptors activation allows the adenylyl cyclase within the airway smooth muscle cells to catalyse the conversion of ATP to cAMP. cAMP as a second messenger further activates protein kinase A and decreases the intracellular calcium level, causing subsequent smooth muscle relaxation.
Common side effects of inhaled β2-adrenergic agonists include tremors, palpitations and headache. The incidence and severity of side effects depend on the dose and route of administration of the β2-adrenergic agonists.
Muscarinic antagonists can compete with acetylcholine for muscarinic receptors and provide an antagonistic effect on muscarinic receptors, causing inhibition of cholinergic bronchomotor tone and hence bronchodilation.
Inhaled muscarinic antagonists commonly cause dry mouth, throat irritation and dizziness.
Systemic administration of glucocorticoids can reduce airway mucus production. It can also suppress inflammatory responses by inhibiting the synthesis and release of inflammatory mediators and lowering the infiltration and activity of inflammatory cells. Additionally, glucocorticoids can increase the amount of β2-adrenergic receptors and their sensitivity towards β2-adrenergic agonists on the airway Smooth muscle.
The use of systemic glucocorticoids may cause depressed immunity, osteoporosis and Cushing’s syndrome. The side effects of glucocorticoids depend on the dose and duration of treatment.
Intravenous magnesium sulfate can reduce calcium ions influx into smooth muscle cells on the airway, causing airway muscle relaxation.
It is possible for intravenous magnesium sulfate to cause hypermagnesemia, resulting in muscle weakness. Intravenous magnesium sulfate is contraindicated in patients with renal insufficiency.
The use of inhaled corticosteroid may commonly cause dysphonia and overgrowth of Oral candidiasis. The risk of overgrowth of oropharyngeal candidiasis can be reduced by rinsing the mouth with water after use.
Muscarinic antagonists can reduce cholinergic bronchomotor tone, resulting in airway muscle relexation and bronchodilation.
Muscarinic antagonists commonly cause dry mouth, throat irritation and dizziness. (2025). 9780646570198, Pharmaceutical Society of Australia. ISBN 9780646570198
Methylxanthines act as a competitive inhibitor of phosphodiesterase, inhibiting phosphodiesterase degradation action of cyclic 3′,5′-adenosine monophosphate (cAMP). This resulted accumulation of cAMP relaxes smooth muscles, leading to dilation of airways.
Methylxanthines activate histone deacetylases, promoting the deacetylation of histone and subsequent DNA folding. This inhibits the synthesis of pro-inflammatory factors that induce asthma attacks and exacerbations, achieving anti-inflammatory effects.
For asthma maintenance therapy, methylxanthines are taken orally.
Therapeutic drug monitoring is required for patients on methylxanthines as the therapeutic range is narrow. Methylxanthines are not routinely used owing to their adverse effect profiles and the risk of toxicity. Adverse effects of Methylxanthines include nervousness, insomnia, irritability, anxiety, gastrointestinal disturbance (nausea, vomiting), tremor, palpitation and increased urine output.
Leukotriene receptor antagonists are taken orally.
Common adverse effects of leukotriene receptor antagonists include headache, abdominal pain and diarrhoea.
For asthma maintenance therapy, mast cell stabilizers are taken by inhalation.
Common adverse effects of Mast cell stabilizers include mouth dryness, cough, throat irritation, nasal congestion and bronchospasm.
Omalizumab binds to free human Antibody to reduce IgE level in circulation. This reduces the subsequent binding of IgE to the IgE receptors on inflammatory cells, including Mast cell, Basophil and Dendritic cell. The release of inflammatory mediators is then prevented.
Mepolizumab and reslizumab inhibit Interleukin (IL)-5 binding with IL-5 receptors on the surface of eosinophils, inhibiting subsequent inflammatory responses.
Benralizumab blocks the IL-5 receptors on basophils, preventing binding of IL-5 with IL-5 receptors on basophils, inhibiting subsequent inflammatory responses.
Dupilumab blocks IL-4 receptors, inhibiting subsequent inflammatory activities of IL-4 and IL-13.
Tezepelumab binds to thymic stromal lymphopoietin (TSLP), which is an inflammatory cytokine in the airway epithelial cells involved in asthma exacerbations, inhibiting subsequent inflammatory responses.
Monoclonal antibodies for the treatment of asthmatic symptoms are given by subcutaneous injections.
Common adverse effects include local site reactions, joint pain, back pain, headache and sore throat.
For newly diagnosed asthma patients, the 5 levels derived from the severity of asthma depend on the occurrence of symptoms and their frequencies. These symptoms include bronchoconstriction, shortness of breath and wheezing that exacerbates after physical activities. Frequent coughing, chest tightness and breathing difficulties are also signs of asthma worsening. These symptoms can interfere with a patient's daily living and affect quality of life. These 5 levels are indicators of what drug treatments should be administered. The guideline is as follows:
Step 1-2: Symptoms less than 4–5 days a week
Step 3: Symptoms most days, or waking with asthma once a week or more
Step 4: Daily symptoms, or waking with asthma once a week or more, and low lung function
Step 5: Further worsening of symptoms and increased occurrence of exacerbations
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