Orciprenaline

Absorption

3% (oral bioavailability of 40%)

Toxicity

Symptoms of overdose include angina, hypertension or hypotension, arrhythmias, nervousness, headache, tremor, dry mouth, palpitation, nausea, dizziness, fatigue, malaise and insomnia. LD50=42 mg/kg (orally in rat).

Originator

Alupent, Boehringer Ingelheim ,W. Germany ,1961

The Uses of Orciprenaline

Bronchodilator.

Indications

For the treatment of bronchospasm, chronic bronchitis, asthma, and emphysema.

Background

A beta-adrenergic agonist used in the treatment of asthma and bronchospasms. [PubChem]

Definition

ChEBI: Metaproterenol is a member of phenylethanolamines.

Manufacturing Process

In an initial operation, 3,5-diacetoxyacetophenone was reacted first with bromine and then with isopropylamine to give 1-(3,5-dihydroxyphenyl)-2- isopropylaminoethanone.
59 g of 1-(3,5-dihydroxy-phenyl)-2-isopropylaminoethanone (free base) were dissolved in 590 cc of methanol, and the solution was hydrogenated in the presence of about 80 g Raney nickel at room temperature and under a pressure of 5 atm. Hydrogen absorption was terminated after a few minutes. The catalyst was separated by vacuum filtration, and the filtrate, an ethanolic solution of 1-(3,5-dihydroxyphenyl)-1-hydroxy-2-isopropylaminoethane, was admixed with the calculated amount of an alcoholic 20% sulfuric acid solution. A crystalline precipitate formed which was filtered off and washed with alcohol. For purification, the product was dissolved in water and the solution was filtered through iron-free charcoal.
Thereafter, the filtrate was evaporated to dryness in vacuo and the residue was taken up in alcohol. The crystalline precipitate which separated out after some standing was separated by vacuum filtration and washed with alcohol. After recrystallization from 90% alcohol, 61 g (83.2% of theory) of 1-(3,5- dihydroxyphenyl)-1-hydroxy-2-isopropylamino-ethane sulfate, MP 202° to 203°C, was obtained.

Therapeutic Function

Bronchodilator

Pharmacokinetics

Orciprenaline (also known as metaproterenol), a synthetic amine, is structurally and pharmacologically similar to isoproterenol. Orciprenaline is used exclusively as a bronchodilator. The pharmacological effects of beta adrenergic agonist drugs, such as orciprenaline, are at least in part attributable to stimulation through beta adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic- 3',5'- adenosine monophosphate (c-AMP). Increased cAMP levels lead to relaxation of bronchial smooth muscles and inhibition of the release of inalammatory mediators from mast cells that are involved in promoting immediate hypersensitivity .

Clinical Use

Metaproterenol was the first β- sympathomimetic drug with metabolic stability to achieve wide clinical use.

Metabolism

Hepatic and gastric. The major metabolite, orciprenaline-3-0-sulfate, is produced in the gastrointestinal tract. Orciprenaline is not metabolized by catechol-0-methyltransferase nor have glucuronide conjugates been isolated to date.