At therapeutic doses, the first- and second-generation antihistamines are equilibrium-competitive inhibitors of H1-receptor-mediated responses. Certain second-generation drugs are noncompetitive inhibitors at high concentrations. Both first- and second-generation compounds have negligible abilities to block the H2-, H3-, or H4-receptors. The therapeutic effectiveness of these
TABLE 38.2 Representative H1Receptor Antagonists
Trade Duration of Sedative Anti-Motion Anticholinergic
Drug Name Action (hr) Activity Sickness Activity Activity
Ethanolamines Carbinoxamine Clemastine Diphenhydramine Dimenhydrinate Ethylenediamines Pyrilamine Tripelennamine
Chlorpheniramine Brompheniramine Piperazines Cyclizine Hydroxyzine Meclizine
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