Asmus MJ. Sherman J. Hendeles L.  Bronchoconstrictor additives in bronchodilator solutions.  Journal of Allergy & Clinical Immunology. 104(2 Pt 2):S53-60, 1999.
Summary
Nebulized bronchodilator solutions are available in the United States as both nonsterile and sterile-filled products. Sulfites, benzalkonium chloride (BAC), or chlorobutanol are added to nonsterile products to prevent bacterial growth, but there have been reports of contaminated solutions containing preservatives. Ethylenediamine tetraacetic acid (EDTA) is added to some products to prevent discoloration of the solution. With the exception of chlorobutanol, all of these additives are capable of inducing bronchospasm in a concentration-dependent manner. However, it is rarely apparent to the patient or health care provider that the additive diminishes the bronchodilator effects. Older products (eg, isoproterenol and isoetharine) contain enough sulfites to produce bronchospasm in most patients with asthma, even in those without a prior history of sulfite sensitivity. Bronchoconstriction from inhaled BAC is cumulative, prolonged, and correlates directly with basal airway responsiveness. The multidose dropper bottle of albuterol contains 50 microgram BAC/dose, which is below the threshold for bronchoconstriction whereas the screw cap unit-dose vial contains 300 microgram/dose, which is above the threshold for many patients. If the screw cap product is used in the emergency department, a patient could receive as much as 1800 microgram of BAC in the first hour. Three sterile-filled unit dose albuterol products contain no additives, whereas a fourth, (manufactured by Dey Laboratories) contains 300 microgram of EDTA, which is also below the threshold dose for bronchoconstriction. Only additive-free sterile solutions should be used for hourly or continuous nebulization of albuterol. The multidose dropper bottle or the Dey product can be used when the interval between doses is longer, whereas the screw cap product should not be used for acute therapy. Ipratropium is available only as a sterile, additive-free unit-dose vial, as is levalbuterol.
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