Isoetarine

Isoetarine (INN) or isoetharine (USAN), trade names Bronkosol and Bronkometer, is a selective beta2-adrenergic receptor agonist. It can be called the "granddaughter of adrenalin" in the line of beta-two antagonists that gave quick relief for brochospasm and asthma. Adrenalin or epinephrine was the first of these, and next came Isuprel. Isoetharine was the third drug in this line, thus the third generation or granddaughter of the original.

In the western US it was the drug of choice in the late 1970s and early 1980s for nebulization ("breathing treatment") to relieve airway spasm. It generally gave sharp relief of shortness of breath, starting within two to five minutes after the patient began breathing the nebulized mist. This rapid onset is not as clearly present in later drugs.

All of the early beta-two agonist catecholamines used for bronchospasm had strong side effects, with increase in heart rate as the most common and most problematic. This came because its "beta-two effect" was not quite as selective as might be hoped. Beta-one receptors appeared to also be stimulated in some patients, causing cardiac and other CNS side effects. With Bronkosol this effect tended to be transient and usually went away within a matter of minutes after the end of the treatment. Increase in blood pressure also occurred in a small but significant percentage of cases, but also was almost invariably transient.

By the late 1980s isoetharine was largely replaced in the marketplace by Alupent/metaproterenol, which seemed to have slightly less cardiac side effect and lasted a couple of hours longer. Alupent in turn was replaced by albuterol. Some practitioners still believe that these later aerosolized bronchodilators never gave quite as quick of relief from asthmatic shortness of breath as did Bronkosol. Thus they see a continued specialty role in treatment of severe shortness of breath that does not improve in the first five minutes of albuterol treatment.

Chemistry

Isoetharine, 3,4-dihydroxy-α-[1-(iso-propylamino)propyl]benzylic alcohol, differs from isoproterenol in the presence of an additional ethyl group in the ethylamino side chain—and is synthesized by bromination of 3,4-dibenzyloxybutyrophenone and the subsequent reaction of the resulting bromo derivative with isopropylamine. The product undergoes reduction by hydrogen using a palladium catalyst, during which the carbonyl group is simultaneously reduced and the benzyl-protecting groups are cleaved forming isoetharine.

• G. Ehrhart, L. Stein, DE 638650  (1936).

References

• George Burton, Respiratory Care, 1984, JB Lippincott, pp. 456–482.
• Craig Scanlan, Egan's Fundamentals of Respiratory Care, 1999, CV Mosby, pp. 571–576.