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Abstract:
The beta 2-adrenergic agonists are reviewed in terms of their dose-response characteristics, and two newer agents, fenoterol hydrobromide and bitolterol mesylate aerosols, are reviewed in relation to older agents. The fenoterol aerosol contains a more potent beta 2-adrenergic agonist dose per puff than the other aerosols but, when given in equipotent doses, offers no advantage over available agents. Bitolterol mesylate is a prodrug that is hydrolyzed to the active beta 2-adrenergic agonist colterol by lung esterases. Bitolterol demonstrates an improved bronchoselectivity in animals, but there are insufficient comparative data in humans. Tachycardia is the dose-limiting toxicity for all beta 2-adrenergic agonists. Currently available data do not suggest an important improvement in duration of action for the newer agents over terbutaline or albuterol. Aerosol administration improves bronchoselectivity of all the agents. Optimal use of beta 2-adrenergic agonist aerosols requires understanding of the variable dose-response characteristics. The type of delivery system and patient technique are important variables in determining the dose delivered. Tube-spacer devices attached to aerosol canisters can significantly improve delivery of the beta 2-adrenergic agonists to the lungs in patients unable to synchronize actuation and inspiration. They provide minimal to no improvement in patients who can perform the appropriate technique. Aerosol administration is the route of choice for beta 2-adrenergic agonists for prophylaxis of exercise-induced bronchospasm; albuterol and terbutaline provide a prolonged duration of action with excellent beta 2-adrenergic selectivity. Patients should be carefully instructed in the optimal use of metered-dose inhalers, and some patients may benefit from use of tube-spacers.