Orciprenaline, also known as orciprenaline (metaproterenol), is a short-acting beta₂-adrenergic agonist used primarily as a bronchodilator in the management of asthma and chronic obstructive pulmonary disease (COPD). It was developed in the mid-20th century as part of early bronchodilator therapy to relieve reversible airway obstruction.
Orciprenaline works by selectively stimulating beta₂ receptors in bronchial smooth muscle, leading to relaxation of airway muscles and improved airflow. It has a relatively rapid onset of action and was historically used for acute relief of bronchospasm, though it has largely been replaced by newer beta₂ agonists with better safety and selectivity profiles.
BRAND NAMES
Alupent – one of the most widely known brand names used as a bronchodilator
Metaprel – another common brand name for orciprenaline in some regions.
MECHANISM OF ACTION
Orciprenaline is a selective beta₂-adrenergic agonist that acts on beta₂ receptors in bronchial smooth muscle. Activation of these receptors stimulates adenylate cyclase, increasing cyclic AMP (cAMP) levels, which leads to relaxation of bronchial smooth muscle and bronchodilation. This reduces airway resistance, improves airflow, and relieves bronchospasm in conditions such as asthma and COPD.
PHARMACOKINETICS
Absorption:
Orciprenaline is well absorbed when administered via inhalation or oral routes, though inhalation is preferred for rapid bronchodilation and reduced systemic effects. It has moderate bioavailability due to first-pass metabolism when taken orally. Onset of action is relatively quick, especially with inhaled forms.
Distribution:
The drug is distributed widely in body tissues after systemic absorption. It has low to moderate plasma protein binding, allowing free drug to act on beta₂ receptors in bronchial smooth muscle.
Metabolism:
Orciprenaline is partially metabolized in the liver by catecholamine-metabolizing enzymes, including conjugation pathways such as sulfation. A portion of the drug remains unchanged, especially after inhalation.
Elimination:
It is primarily excreted in urine as inactive metabolites, with a small fraction eliminated unchanged. The duration of action is short, contributing to its classification as a short-acting beta₂ agonist.
PHARMACODYNAMICS
Orciprenaline is a selective beta₂-adrenergic receptor agonist. It stimulates beta₂ receptors in bronchial smooth muscle, activating adenylate cyclase and increasing cyclic AMP levels. This leads to relaxation of airway smooth muscle, resulting in bronchodilation, improved airflow, and relief from bronchospasm in conditions such as asthma and COPD.
ADMINISTRATION
Orciprenaline is administered via inhalation (preferred), oral tablets, or injectable forms in some settings. It is used for rapid relief of bronchospasm but is less commonly used today due to newer, more selective bronchodilators.
DOSAGE AND STRENGTH
Orciprenaline is available in inhaler and tablet formulations, with dosing varying by indication and severity. Inhaled doses are typically repeated several times daily as needed, while oral dosing is divided throughout the day for bronchodilation support.
DRUG INTERACTIONS
Orciprenaline may interact with non-selective beta-blockers, which can reduce its bronchodilatory effect. Concomitant use with other sympathomimetic drugs may increase the risk of cardiovascular side effects such as tachycardia and arrhythmias.
FOOD INTERACTIONS
No significant food interactions are known. Oral absorption may be slightly affected by gastrointestinal conditions but is generally not clinically significant.
CONTRAINDICATIONS
Orciprenaline is contraindicated in patients with hypersensitivity to the drug. Caution is required in patients with significant cardiac arrhythmias, tachycardia, or severe cardiovascular disease.
SIDE EFFECTS
Tremor
Palpitations
Headache
Nervousness
Tachycardia
OVER DOSAGE
Overdose of orciprenaline, a beta₂-adrenergic bronchodilator, results from excessive stimulation of the sympathetic nervous system. Symptoms may include marked tachycardia, palpitations, tremors, anxiety, headache, flushing, and dizziness. In more severe cases, it can cause hypotension or hypertension, hypokalemia (low potassium levels), and cardiac arrhythmias, which may become life-threatening if untreated.
TOXICITY
Overdose of orciprenaline may lead to excessive beta-adrenergic stimulation, causing severe tachycardia, hypertension or hypotension, tremors, hypokalemia, and cardiac arrhythmias. Management is supportive, with monitoring of cardiovascular status and correction of electrolyte disturbances.
