Asthma Pharmacology

Updated: May 26

Asthma is a chronic inflammatory disease of the airways, that causes hyperresponsiveness,  increased mucus production and mucosal oedema.


What this means is that Asthma is a long-term condition where the body has an extreme allergic reaction to environmental factors such as dust, pollen or animal dander. When triggered, this reaction causes inflammation in the airways which in turn causes excessive mucus production and swelling of the airways.


In these notes, we’ll be going over the Asthma Pharmacology, but before getting into that, make sure that you’ve understood the:

  1. Anatomy & Physiology of the Respiratory System

  2. The Pathophysiology of Asthma

 

Introduction to Asthma Pharmacology

As we’ve discussed in the previous notes, the main concern in Asthmatic patients is the persistent and repetitive inflammation of the airways. To treat this, most medical providers will prescribe inhaled anti-inflammatory medication. This mode of administration will directly target the lungs and allow for a more effective treatment approach.

Keep in mind that asthmatic patients alternate between periods of exacerbations and longer periods of mild symptoms. Similarly, the medications for Asthma are split into two:

  1. The Short-Acting Medications are indicated for exacerbations and severe asthmatic symptoms. As well as preventive in exercise-induced asthma

  2. The Long-Acting Medications are indicated to control chronic Asthma symptoms.

Short-Acting Asthma Pharmacology

There are three main classes used for the quick relief of asthma symptoms, and these include:

  1. Short-Acting Beta-2 Adrenergic Agonists (SABA)

  2. Anticholinergics

  3. Corticosteroids

The SABA and the Anticholinergics are typically both prescribed as inhalers, and both act as bronchodilators but their mechanisms are slightly different. SABAs will bind to the Beta-2 Adrenergic receptor and relax the smooth muscle, which in turn reduces bronchoconstriction. On the other hand, Anticholinergics inhibit the Muscarinic Cholinergic receptors and decrease the vagal tone of the airways. They also suppress the mucous gland secretion which helps to unplug the airways.


Corticosteroids however are typically prescribed as oral medication and act as Anti-Inflammatories. They stop the body’s reaction to the allergen decreasing the hyperresponsiveness, inhibiting cytokine production and revere the Beta-2 Receptor Downregulation. All together they reduce the inflammation and swelling of the airways.

Table 1: Short-Acting Asthma Pharmacology


Class

Generic Names

Side Effects

Drug Interactions

Short-Acting Beta-2 Adrenergic Agonists

Albuterol Levabuterol HFA Metaprotenol Sulfate

Tachycardia

Headache

Muscle Tremor

Paradoxical Bronchospasm

Cardiovascular effects

Hyperglycaemia

Hypokalemia

Beta-Blockers

Digoxin

Non-Potassium Sparing Diuretics

Anticholinergics

Ipratropium

Dry mouth

Wheezing

Cough

Paradoxical Bronchospasm

Ocular Effects

Urinary Retention

No known drug interactions

Corticosteroids

Methylprednisolone Prednisolone

Prednisone

Weight-gain

Fluid retention

Hypertension

Peptic ulcers

Insomnia

More susceptible to infections

Live vaccines

Amphotericin B injection

Potassium-Depleting Agents

Antibiotics

Antidiabetics


Long-Acting Asthma Pharmacology

When it comes to the long-term treatment of Asthma there is a vast range of options and it all depends on the severity of the condition and the symptoms that it is presenting with. The most common long-term approach is Corticosteroids, this is because they are highly effective in treating the symptoms of Asthma, increasing airway function and reducing the peak flow variability.


Corticosteroids are usually prescribed as inhalers when managing chronic Asthma, but they are sometimes used in systemic ways (oral/intra-muscular) if the patient has severe and persistent symptoms, needs to quicken recovery or wants to prevent future exacerbations. Despite the number of advantages that corticosteroids have, several side effects work against their goal particularly the fact that they make patients more susceptible to acquiring respiratory infections.


Long-Acting Beta-2 Adrenergic Agonists (LABAs) are typically prescribed alongside anti-inflammatories to treat chronic asthmatic symptoms, especially symptoms that flare up during the night or exercise.


Leukotrienes are a group of Inflammatory Mediators, which are released by the body to block an allergen and fuel hyperresponsiveness. So Leukotriene Inhibitors do exactly the opposite, they block the production of Leukotrienes and in turn, stop bronchoconstriction. This class of medications can either be used instead of Corticosteroids or added along with inhaled corticosteroids if the patient’s condition is more advanced.


Phosphodiesterase Inhibitors affect the release of epinephrine, giving them mild anti-inflammatory properties, and they also act as bronchodilators. Theophylline is a type of phosphodiesterase inhibitor and it’s sometimes prescribed in addition to inhaled corticosteroids to treat asthmatic symptoms. However, it is used with high caution as it interacts with a lot of drugs and can cause severe side effects.


Lastly, if the patients do not respond well to treatment of high-dose inhaled corticosteroids even if given with a LABA, they would usually receive Immunomodulators either subcutaneously or intravenously. These Immunomodulators stop IgE from binding to receptors and in turn, they prevent bronchospasm, mucus hypersecretion and airway hyperresponsiveness.


So in total, we’ve mentioned 7 different medications that can be used to treat chronic asthma:

  1. Inhaled Corticosteroids

  2. Systemic Corticosteroids

  3. Long-Acting Beta-2 Adrenergic Agonists

  4. Phosphodiesterase Inhibitors

  5. Leukotriene Modifiers

  6. 5-Lipoxygenase Inhibitor

  7. Immunomodulators

Table 2: Long-Acting Asthma Pharmacology


Class

Generic Names

Side Effects

Drug Interactions

Inhaled Corticosteroids

Beclomethasone Dipropionate

Budesonide Ciclesonide

Fluticasone

Cough

Dyspnoea

Headache

Adrenal insufficiency

Dermal thinning

Paradoxical Bronchospasm

Dental and oral damage

CYP3A4 Inhibitors

Long-term Ketoconazole

Systemic Corticosteroids

Methylprednisolone Prednisolone

Prednisone

Adrenal axis suppression

Dermal thinning

Hypertension

Diabetes

Cushing’s syndrome

Cataracts

Muscle weakness

Insomnia

Cyclosporin

Aspirin

Phenobarbital

Phenytoin

Rifampin


Long-Acting Beta-2 Adrenergic Agonists (Inhaled)

Salmeterol

Formoterol

Tachycardia

Muscle tremor

Hypokalemia

Decreased protection against exercise induced bronchospasm

CYP450 3A4 Inhibitors

Monoamine Oxidase Inhibitors

Tricyclic Antidepressants

Beta-Adrenergic Receptor Blocking Agents

Non-Potassium Sparing Diuretics

Phosphodiesterase Inhibitors

Theophylline

Insomnia

Gastric upset

GERD

Peptic ulcers

Dipyridamole

Febuxostat

Riociguat

(full list here.)

Leukotriene Modifiers

Montelukast

Zafirlukast

Headache

Dizziness

Upper respiratory infections

Pharyngitis

Sinusitis

Idelalisib

Ivacaftor

5- Lipoxygenase Inhibitor

​Zileuton

Elevated liver enzymes

Theophylline

Warfarin

Propranolol

Immunomodulators

Omalizumab

Mepolizumab

Reslizumab (IV)

Dupilumab

Muscle aches

Bruising

Irritation of skin on injection sites

No formal drug interactions have been performed




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