The discovery of H-, receptor antagonists has proved to be a significant breakthrough in the treatment of allergic diseases. Chemical modifications of these early agents have yielded the second-generation antihistamines, which are of equal antagonistic efficacy but have fewer side effects because of their lipophobic structures. Newer nonsedating antihistamines, which are metabolites or isomers of existing agents, are now under development. H 2 receptor antagonists have been found extremely useful in the treatment of peptic ulcer disease. However, they have been disappointing in the treatment of allergic and immunologic disorders in humans. Newer selective nonsedating H-, antagonists and dual-action antihistamines, because of their lower side-effect profiles, have provided therapeutic advantages over first-generation agents for long-term management of allergic rhinitis.
Prescription of H-, antagonists should follow a practical, stepwise approach. Because there are virtually dozens of antihistamine preparations available with or without decongestants, it is recommended that physicians become familiar with all aspects of a few agents from each structural class. Appropriate selection of one of these antihistaminic agents will satisfy the patient's clinical needs in most instances.
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