Asmalin MDI Mechanism of Action

Pharmacology: Pharmacodynamics: Salbutamol is a selective short-acting beta₂-agonist with a preferential effect on beta₂-receptors found in the respiratory tract. It stimulates adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3',5'-adenosine monophosphate (cAMP). cAMP mediates cellular responses such as bronchial smooth muscle relaxation resulting in bronchodilation.
Pharmacokinetics: Salbutamol is readily absorbed from the gastrointestinal tract after oral administration. When given by inhalation, 10% to 20% of the dose reaches the lower airways. The remainder is retained in the delivery system or is deposited in the oropharynx from where it is swallowed. Plasma protein binding is around 10%.
Salbutamol undergoes first-pass metabolism in the liver, being converted to salbutamol 4'-O-sulfate. The plasma half-life of salbutamol has been estimated to range from 4 to 6 hours. Salbutamol is rapidly excreted, mainly in the urine, as metabolites and unchanged drug; a smaller proportion is excreted in the feces. Majority of a salbutamol dose given orally or by inhalation is excreted within 72 hours.
Bronchodilation begins within 5 to 15 minutes after oral inhalation of salbutamol and peaks in 0.5 to 3 hours. The mean duration of effect persists for at least 4 hours. In some patients, bronchodilation may persist up to 6 hours.