Asmalin Mechanism of Action

Pharmacology: Pharmacodynamics: Salbutamol is a selective short-acting beta₂-adrenergic agonist with a preferential effect on beta₂-adrenergic 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: Syrup: 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 30 minutes after oral administration of salbutamol, peaks in 2 to 3 hours, and persists 4 to 6 hours.
Pulmoneb: Onset of bronchodilation is within 5 minutes after nebulization with Salbutamol, peaks in 1 to 2 hours, and persists for 3 to 4 hours. Bronchodilation generally persists up to 6 hours or longer. After inhalation of nebulized Salbutamol, less than 20% of the drug is absorbed in the lungs. The remaining amount is retained in the nebulizer and recovered in expired air. Much of the Salbutamol dose delivered by oral inhalation is deposited on the buccal mucosa and subsequently swallowed and absorbed from the gastrointestinal tract.
Salbutamol is metabolized in the liver, being converted to Salbutamol 4'-O-sulfate. This is then excreted in the urine and feces. In patients with asthma, about 70% of the inhaled dose is excreted in urine as unchanged drug and metabolites within 24 hours, and 80 to 100% within 72 hours. About 30% of the inhaled dose is excreted unchanged in the urine in 24 hours. About 10% of the inhaled dose may be excreted in the feces.
Animal studies show that Salbutamol can cross the blood-brain barrier and the placenta. It may be secreted in breast milk but the concentrations are not known.