Short Acting Beta-2 Agonists

Introduction
Illustrated mechanism of action
Examples of Medication Brand Names (with Images)
Indication
Side Effects
Precautions & Contraindications
Monographs
Reference

Introduction

History

Short-acting beta-2 agonists (SABAs) are medications primarily used as "rescue" inhalers to provide rapid relief from bronchospasm in conditions like asthma and chronic obstructive pulmonary disease (COPD). They work by selectively stimulating beta-2 adrenergic receptors on airway smooth muscle, leading to muscle relaxation and bronchodilation, which opens the airways and improves airflow.

Common FDA-approved SABAs include albuterol, levalbuterol, metaproterenol, and terbutaline. These drugs typically start working within minutes and are used to quickly alleviate acute symptoms such as wheezing, shortness of breath, and chest tightness.

SABAs are essential in frontline management for asthma and COPD exacerbations but should be used cautiously, as overuse is linked to poor asthma control and increased risk of adverse outcomes. They are generally administered via inhalers or nebulizers for targeted delivery to the lungs, minimizing systemic side effects.

Illustrated mechanism of action

* SABAs selectively bind to beta-2 adrenergic receptors on airway smooth muscle cells.

* This activates a stimulatory G protein coupled to the receptor.

* The G protein activates adenylyl cyclase enzyme.

* Adenylyl cyclase converts ATP to cyclic AMP (cAMP), increasing intracellular cAMP levels.

* Elevated cAMP activates protein kinase A (PKA).

* PKA decreases intracellular calcium and inactivates myosin light-chain kinase.

* This leads to relaxation of airway smooth muscle and bronchodilation.

* SABAs also open calcium-activated potassium channels, hyperpolarizing smooth muscle cells.

* They inhibit release of bronchoconstrictor mediators from mast cells.

* The overall effect is rapid airway opening and relief of bronchospasm, lasting 3–6 hours.

Examples of Medication Brand Names (with Images)

Terbutaline

Albuterol

Pirbuterol

Levalbuterol

Fenoter

Indication

01

"Relief of acute bronchospasm" in asthma and chronic obstructive pulmonary disease (COPD) by rapidly relaxing airway smooth muscle to open airways.

02

"Quick relief of asthma symptoms" during exacerbations, providing symptom relief that lasts about 3 to 4 hours.

03

"Prevention and treatment of exercise-induced bronchoconstriction (EIB)", taken before exercise to prevent airway narrowing.

04

"Management of reversible airway obstruction" in bronchial asthma and COPD, improving airflow and breathing.

05

"Use in acute exacerbations of COPD", sometimes requiring higher doses or more frequent administration due to reduced drug duration during exacerbations.

Side Effects

hypotention

bradycardia

(AV-Block)

Drowsiness Depression

Symptoms of CHF

Precautions & Contraindications

Precautions for short-acting beta-2 agonists (SABAs) like salbutamol include:

● Avoid over-reliance on SABAs as they only relieve symptoms temporarily and do not control the underlying disease; increasing use may indicate worsening condition needing medical review.

● Use with caution in patients with cardiovascular conditions such as coronary artery disease, arrhythmias, uncontrolled hypertension, and in those with diabetes or convulsive disorders.

● Monitor for side effects like tremors, headache, muscle cramps, tachycardia, palpitations, and rare serious effects such as hypokalemia, cardiac arrhythmias, and lactic acidosis especially at high doses or overdose.

● Frequent use of SABAs can lead to reduced drug effectiveness over time due to beta-2 receptor desensitization (tolerance), which may require adjustment of the treatment plan.

● Patients should be instructed on correct inhaler technique and supervised initially to ensure effective and safe use.

● Inform healthcare providers if using SABAs more than twice a week, as this suggests unstable asthma requiring adjustment of long-term control therapy.

● Use cautiously during pregnancy and breastfeeding; benefits and risks should be evaluated by a doctor.

● Avoid concomitant use with drugs that prolong the QT interval or interact adversely (e.g., certain antibiotics, antidepressants).

Contraindications of Short-Acting Beta-2 Agonists (SABAs):

These drugs are generally well-tolerated, but there are specific situations where their use is contraindicated or requires extreme caution.

●Main Contraindications:

1》Known hypersensitivity to the drug or any of its components.

May lead to allergic reactions like rash, angioedema, or anaphylaxis.

2》Severe cardiac disorders, especially:

Tachyarrhythmias (e.g., atrial fibrillation, ventricular tachycardia).

Severe ischemic heart disease or recent myocardial infarction.

3》Uncontrolled hyperthyroidism, due to increased sensitivity to sympathomimetic effects.

4》Patients with risk of QT interval prolongation, especially if taking other QT-prolonging drugs (risk of torsade's de pointes).

5》History of paradoxical bronchospasm following previous inhalation of a beta-2 agonist (a rare but serious reaction where the drug worsens breathing).

Monographs

Drug monograph mariam wael .pdf

Levalbuterol

Drug monograph copy 2.docx

Pirbuterol

Drug monograph.docx_20250324_223439_٠٠٠٠.pdf

Fenoterol

ph mohammed.pdf

Albutero (Sulbutamol)

Drug monograph.docx_20250323_191452_٠٠٠٠.docx

Terbutaline

Reference