pirbuterol

Action and Spectrum

Actions and Spectrum: 

• Bronchodilation: The primary action of pirbuterol is bronchodilation. It acts as a selective beta-2 adrenergic agonist, which binds to and activates beta-2 adrenergic receptors in the smooth muscle of the airways. Activation of these receptors leads to relaxation of the bronchial smooth muscle, causing dilation of the airways and improved airflow. This effect helps to relieve acute bronchospasm and ease breathing difficulties in patients with asthma or COPD. 
• Prevention of Exercise-Induced Bronchospasm (EIB): pirbuterol can also be used as a preventive measure to manage exercise-induced bronchospasm. When administered before physical activity, pirbuterol helps to prevent bronchoconstriction triggered by exercise, enabling patients to engage in physical activities without experiencing asthma-related symptoms. 
• Onset and Duration of Action: pirbuterol is classified as a short-acting beta-agonist (SABA), which means it has a rapid onset of action and provides quick relief of bronchospasm. Typically, the bronchodilatory effects of pirbuterol start within minutes after inhalation and last for about 4 to 6 hours. Due to its short duration of action, pirbuterol is primarily used for acute symptom relief and as a rescue medication for acute exacerbations of asthma or COPD. 
• Limited Anti-inflammatory Effects: It’s important to note that pirbuterol primarily provides bronchodilation and does not have significant anti-inflammatory properties. Therefore, it is not considered a substitute for long-term control medications, such as inhaled corticosteroids, used to manage chronic airway inflammation in patients with persistent asthma or COPD. 

Drug Interaction

Adverse Reaction

Frequency not defined 

Nervousness 

Restlessness 

Serum glucose increased 

Serum potassium decreased 

Trembling 

Palpitations 

Tachycardia 

CoughHeadache 

Dizziness 

Lightheadedness 

Taste changes 

Vomiting 

Nausea 

Paradoxical bronchospasm 

Black Box Warning

Black Box Warning: 

None 

Contraindication / Caution

Contraindication/Caution: 

Contraindications: 

• Hypersensitivity 
• Severe cardiovascular disorders 

Cautions: 

• Cardiovascular conditions 
• Seizures 
• Diabetes 
• Pregnancy 
• Lactation 
• Tolerance  
• Overuse 

Pregnancy / Lactation

Pregnancy consideration:  

Pregnancy category: C 

Breastfeeding warnings:  

The excretion of the drug in breast milk is unknown; hence not recommended in lactating females. 

Pregnancy category: 

Category A: well-controlled and satisfactory studies show no risk to the fetus in the first or later trimester. 

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women. 

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.    

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.    

Category N: No data is available for the drug under this category. 

Pharmacology

Pharmacology:  

pirbuterol is a short-acting beta-2 adrenergic receptor agonist bronchodilator. It is structurally related to other beta-agonists like albuterol and terbutaline. pirbuterol’s pharmacological effects are primarily mediated through its interactions with beta-2 adrenergic receptors in the smooth muscles of the airways. 

Pharmacodynamics: 

• Beta-2 Adrenergic Receptor Agonist: pirbuterol is a selective beta-2 adrenergic receptor agonist that relaxes and activates beta-2 adrenergic receptors. These receptors are predominantly found in the smooth muscles of the bronchioles and bronchi in the lungs. 
• Bronchodilation: Upon binding to beta-2 receptors, pirbuterol triggers intracellular events that relax the smooth muscles surrounding the airways. This bronchodilation causes the bronchioles to widen and the airways to open up, which results in improved airflow into and out of the lungs. 
• Reduction of Airway Resistance: The bronchodilatory effect of pirbuterol leads to a reduction in airway resistance. By relaxing the smooth muscles, the drug decreases the resistance to airflow, making it easier for the patient to breathe. 

Pharmacokinetics: 

Absorption 

pirbuterol is commonly administered via inhalation, typically as an aerosol or metered-dose inhaler (MDI). Inhalation allows the drug to be delivered directly to the lungs, where it exerts its bronchodilatory effects. Inhalation also facilitates the rapid onset of action, as the drug can quickly reach its target site of action. 

Distribution 

After absorption through inhalation, pirbuterol quickly enters the bloodstream and is distributed throughout the body. The drug’s distribution is primarily limited to the tissues with beta-2 adrenergic receptors, such as the bronchial smooth muscles in the lungs. 

Metabolism 

pirbuterol undergoes metabolism primarily in the liver, where it is metabolized into inactive compounds. The main metabolic pathway involves conjugation with glucuronic acid, resulting in the formation of inactive glucuronide metabolites. The metabolites are then excreted from the body. 

Elimination and Excretion 

The excretion of pirbuterol and its metabolites occurs mainly through the kidneys. 

The elimination half-life is 2 hours. 

After metabolism, the inactive glucuronide metabolites are filtered by the kidneys and eliminated through urine. Only a tiny fraction of the unchanged drug is excreted in the urine. 

Adminstartion

Administration: 

• Shake the MDI well to ensure proper medication mixing 
• Start by exhaling fully to empty the lungs. 
• Hold the inhaler erect with the mouthpiece at the bottom and close the tap 
• Tilt your head slightly backward and breathe out slowly and thoroughly 
• Place the mouthpiece between your teeth without biting down and form a tight seal with your lips around it 
• Start breathing in slowly and deeply through your mouth while simultaneously pressing down on the canister to release the medication 
• Hold your breath for about 10 seconds to allow absorption of the medication into the airways 
• Exhale slowly through the nose 
• If a second dose is required, wait at least one minute before repeating the inhalation process 

Patient Information Leaflet

Patient information leaflet 

Generic Name: pirbuterol 

Pronounced as: pir-BUE-ter-ol 

Why do we use pirbuterol? 

pirbuterol is used primarily as a bronchodilator to quickly relieve acute bronchoconstriction, asthma, and chronic obstructive pulmonary disease (COPD) symptoms. It belongs to the class of short-acting beta-2 adrenergic receptor agonists (SABAs).