Introduction of Drug: Methacholine is a synthetic choline ester that acts as a selective agonist for muscarinic receptors. It is commonly us...
Introduction of Drug:
Methacholine is a synthetic choline ester that acts as a selective agonist for muscarinic receptors. It is commonly used in pulmonary function testing to assess airway responsiveness in individuals suspected of having asthma.
Normal Physiology:
In normal physiology, the airways have a certain level of responsiveness to various stimuli. However, in individuals with asthma, the airways are hyperresponsive, meaning they tend to constrict more readily in response to certain triggers, leading to symptoms such as wheezing, coughing, and shortness of breath.
Mechanism of Action:
Methacholine selectively activates muscarinic receptors, particularly the M3 subtype, present in the smooth muscle of the airways. This activation stimulates intracellular signaling pathways through G proteins, resulting in smooth muscle contraction and bronchoconstriction.
Indications:
The primary indication for methacholine is in pulmonary function testing, specifically the methacholine challenge or bronchial provocation test. It is used to assess airway hyperresponsiveness, a characteristic feature of asthma. The test helps in confirming the diagnosis of asthma and determining the severity of the condition.
Side Effects:
Methacholine challenge tests can induce bronchoconstriction, resulting in symptoms such as coughing, wheezing, shortness of breath, and chest tightness. These side effects are temporary and typically resolve after the test is completed. In rare cases, severe bronchoconstriction requiring medical intervention may occur.
Pharmacokinetic Profile:
Methacholine is administered via inhalation as a solution or aerosol. After inhalation, it is rapidly absorbed through the respiratory tract and enters systemic circulation. The onset of action is relatively quick, and the duration of the bronchoconstrictive effect depends on the individual's airway responsiveness and the concentration of methacholine administered.
ADRs (Adverse Drug Reactions):
The main adverse reactions associated with methacholine use are related to its bronchoconstrictive effects during the challenge test. These may include coughing, wheezing, shortness of breath, chest discomfort, and in rare cases, severe bronchoconstriction requiring medical intervention. Adverse reactions specific to systemic exposure are uncommon since the drug is mainly administered via inhalation.
No comments