What is the use and mechanism of action of Orciprenaline (Metaproterenol)?

From the Guidelines

Orciprenaline (Metaproterenol) is a selective beta-2 adrenergic receptor agonist used to treat asthma and other respiratory conditions by relaxing bronchial smooth muscle and improving airflow to the lungs. The mechanism of action of orciprenaline involves binding to beta-2 receptors in the bronchial smooth muscle, activating adenylyl cyclase, and increasing intracellular cyclic AMP levels, which leads to relaxation of the bronchial smooth muscle and widening of the airways 1. Some key points about orciprenaline include:

• It has a relatively short duration of action (4-6 hours) compared to newer beta-2 agonists
• The typical adult dosage is 10-20 mg taken orally three to four times daily, or 1-2 inhalations (0.65-1.3 mg) every 3-4 hours when used as an inhaler
• Side effects may include tremor, nervousness, increased heart rate, and palpitations due to its partial activity on beta-1 receptors in the heart
• This medication has largely been replaced by more selective beta-2 agonists like salbutamol (albuterol) and formoterol, which have fewer cardiac side effects and longer durations of action. It's worth noting that while epinephrine, a non-selective alpha and beta-adrenergic agonist, is sometimes used in acute asthma treatment, especially in cases of anaphylaxis or angio-oedema, orciprenaline's selective beta-2 agonist activity makes it a more targeted therapy for bronchospasm with potentially fewer side effects compared to non-selective agonists like epinephrine 1.

From the Research

Mechanism of Action of Orciprenaline (Metaproterenol)

• Orciprenaline, also known as metaproterenol, is a bronchodilator that works by stimulating β2-adrenoceptors (β2-ARs) on airway smooth muscle to mimic the sympathetic influence on the lung 2.
• The stimulation of β2-ARs leads to relaxation of airway smooth muscle, resulting in bronchodilation and relief of bronchoconstriction 3, 4.

Use of Orciprenaline (Metaproterenol)

• Orciprenaline is used in the treatment of asthma and other airway disorders, such as chronic obstructive pulmonary disease (COPD) 5, 2.
• It can be administered by inhalation, oral, or injectable routes, with the inhalation route being the most common 5.
• The use of orciprenaline in combination with other bronchodilators, such as long-acting muscarinic acetylcholine receptor antagonists (LAMAs), has been shown to have additive/synergistic effects 2.

Comparison with Other Bronchodilators

• Orciprenaline has been compared to other beta-adrenergic stimulants, such as salbutamol, isoproterenol, and procaterol, in terms of its bronchodilating effects 3, 4.
• Salbutamol was found to be superior to orciprenaline in terms of bronchodilation and duration of action 3.
• Orciprenaline was found to have a similar bronchodilating effect to isoprenaline and salbutamol, but with a lower increase in heart rate and systolic blood pressure compared to isoprenaline 4.