metaproterenol

Action and Spectrum

Actions and Spectrum 

Metaproterenol acts on the beta-2 adrenergic receptors which are on the smooth muscles of the airways.
When these receptors are stimulated metaproterenol favours relaxation and dilatation of the bronchial smooth muscles.
Since metaproterenol is selective for Beta-2 adrenergic receptors primarily in the bronchi smooth muscles, this drug acts highly selectively on these receptors.
Because of its broncho dilatory effects it is applied in conditions with bronchospasm obstructive airway diseases like asthma, chronic bronchitis.

Drug Interaction

Adverse Reaction

Adverse Reaction  

Frequency defined  

<1% 

Syncope

Spasms

Chest pain

Hypertension

Weakness

1-10% 

Heartburn (4%)

Diaphoresis increased (4%)

Insomnia (2%)

Exacerbation of asthma (2%)

Palpation (4%)

Nausea (1-4%)

Weakness (1%)

Dizziness (1-4%)

Headache (4%)

Pharyngitis (4%)

>10% 

Nervousness (5-20%)

Tachycardia (6-17%)

Tremor (2-17%)

Black Box Warning

Black Box Warning 

Metaproterenol does not have any black box warning.

Contraindication / Caution

Contraindication/Caution: 

Contraindication: 

known hypersensitivity or allergy to metaproterenol

Caution: 

Underlying cardiovascular disorders

Diabetic patients

Hyperthyroidism

Pregnancy / Lactation

Pregnancy/Lactation 

Pregnancy warnings:  

Pregnancy category: C

Lactation: Excretion into human milk is unknown

Pregnancy Categories:   

Category A:  well-controlled and Satisfactory studies show no risk to the fetus in the first or later trimester.

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women.

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.

Category N: There is no data available for the drug under this category.

Pharmacology

Pharmacology

Metaproterenol act on the beta-2 adrenergic receptors which are predominant in smooth muscles of the airways.

Metaproterenol attaches to beta-2 adrenergic receptors and overlays with adenylyl cyclase, which then converts adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP).

Pharmacodynamics

Centrally acting agents like metaproterenol help in bronchial smooth muscles relaxation because of composure of beta-2 adrenergic receptor.

Among the effects of metaproterenol stimulation of the blood vessel’s beta-2 adrenergic receptors have vasodilating effect that occurs particularly in muscles.

In counteracting the effects of chemical mediators, metaproterenol prevents the release of histamine and leukotrienes that cause instability in the mast cells.

Pharmacokinetics

Absorption

By oral administration metaproterenol is rapidly absorbed by the digestive tract. It can reach the lungs through the process of inhalation, where it is also can quickly begin showing its bronchodilator effects.

Distribution

Metaproterenol’s has moderate volume of distribution.

This medication is known to cross the placenta, the blood-brain barrier and is also secreted in breast milk.

Metabolism

Metaproterenol is mainly excreted by conjugation with glucuronic acid formed in the liver. The major metabolic pathway is consequent to O-methylation of metaproterenol by catechol-O-methyltransferase.

Elimination and excretion

Metaproterenol is mostly metabolized and excreted by the kidneys; however, a minor amount is metabolized by the liver and lungs.

Metaproterenol has a short elimination half-life to be about 3 to 4 hours.

Adminstartion

Administration

An MDI is an alternative for delivering the aerosol form of metaproterenol.

One way is using a nebulizer that converts the medicine into a mist which the patient can breathe in.

Metaproterenol can also be taken as oral tablet and syrup.

Patient Information Leaflet

Patient information leaflet 

Generic Name: metaproterenol

Why do we use metaproterenol? 

Respiratory disorders such as bronchospasm and airway obstruction are diseases for which metaproterenol is used to manage.

In this case, metaproterenol is used as a reliever drug to respond to the urgent demand for treating acute bronchospasm in asthmatic patients.

Due to it increasing lung capacity and decreasing bronchospasm, metaproterenol may be advised to patients suffering from COPD with chronic bronchitis or emphysema.