Pirbuterol (trade name Maxair) is a short-acting β2 adrenoreceptor agonist with bronchodilating action used in the treatment of asthma, available (as pirbuterol acetate) as a breath-activated metered-dose inhaler. It acts selectively on β2 receptors on bronchial smooth muscle to increase intracellular cAMP and produce rapid bronchodilation with an onset of action within minutes and a clinical duration typically in the short-acting range. The molecule is formulated as the acetate salt to optimize stability and aerosol performance; systemic exposure after inhalation is low due to limited oral bioavailability and mainly pulmonary absorption, with metabolic clearance by hepatic pathways and renal elimination of metabolites. Formulation and device controls focus on dose uniformity, plume characteristics and particle-size distribution to ensure delivery to the lower airways while minimizing oropharyngeal deposition.
Typical quality-control specifications for pirbuterol drug substance and finished inhalation product monitor both process-related and degradation impurities; common categories include oxidative products, N-oxide species, dealkylated and deaminated derivatives, positional isomers and residual synthetic intermediates. Example analytical limits used in registration and release testing are individual unidentified impurities not greater than 0.10% w/w, any single specified related compound typically limited to the range 0.05 to 0.30% w/w depending on toxicological qualification, total impurities not greater than 0.50% w/w, assay acceptance commonly 98.0 to 102.0% of label claim, water content controlled (for example ≤0.5% by Karl Fischer) and heavy metals limited to low ppm levels (for example ≤10 ppm); residual solvents are controlled in accordance with ICH Q3C and specified per solvent class. Batch release relies on validated HPLC or UPLC methods with orthogonal impurity identification by MS or NMR when required.
Pirbuterol is used as a bronchodilator for relief and prevention of bronchospasm in patients with reversible obstructive airway disease, including acute symptomatic relief and prevention of exercise-induced bronchospasm.
Pirbuterol is a short-acting beta2 agonist, abbreviated SABA.
Availability has declined and pirbuterol in the Maxair formulation has been discontinued or withdrawn in several markets; current availability depends on national regulatory status and local suppliers, so check regional prescribing information or national formularies for up-to-date supply status.
Pirbuterol belongs to the class of short-acting sympathomimetic bronchodilators acting as selective β2-adrenoreceptor agonists.
