Asmacaire Solution For Inhalation Mechanism of Action

Pharmacology: Salbutamol is a direct-acting sympathomimetic with predominantly beta-adrenergic activity and a selective action on beta₂ receptors (a beta₂ agonist). This results in its bronchodilating action being more prominent than its cardiovascular effect.
Administration by inhalation results in the rapid onset (within 5 to 15 minutes) of bronchodilation which lasts for about 3 to 6 hours.
Pharmacokinetics: Salbutamol is readily absorbed from the gastrointestinal tract. It is subject to first-pass metabolism in the liver and possibly in the gut wall: the main metabolite is an inactive sulfate conjugate.
Salbutamol is rapidly excreted in the urine as metabolites and unchanged drug; there is some excretion in the faeces. It does not appear to be metabolized in the lung, therefore its ultimate metabolism and excretion following inhalation depends upon the delivery method used, which determines the proportion of inhaled salbutamol relative to the proportion inadvertently swallowed. It has been suggested that the majority of an inhaled dose is swallowed and absorbed from the gut.
The plasma half-life of salbutamol has been estimated to range from 4 to 6 hours.
Following inhalation, salbutamol sulfate acts topically in bronchial smooth muscle and initially the drug is undetectable in the blood. After 2 to 3 hours low concentrations are seen, due presumably tothe portion of the dose which is swallowed and absorbed in the gut.
The elimination half-life of inhaled or oral salbutamol sulfate is between 2.7 and 5 hours.
Salbutamol sulfate is not metabolized in the lung but is converted to the 4'-0 - sulphate ester in the liver. Salbutamol sulfate is excreted in the urine as free drug and as the metabolite. After oral administration 58-78% of the dose is excreted in the urine in 24 hours, approximately 60% as metabolites, a small fraction is excreted in the feces.