H1-receptor antagonists: safety issues.
Histamine is an important neurotransmitter. Old (first-generation) H1-receptor antagonists such as chlorpheniramine, diphenhydramine, or triprolidine produce histamine blockade at H1-receptors in the central nervous system (CNS) and frequently cause somnolence or other CNS adverse effects. New (second generation) H1-antagonists such as cetirizine, fexofenadine, and loratadine represent an advance in therapeutics; in manufacturers' recommended doses, they enter the CNS in smaller amounts, produce relatively little somnolence or other CNS adverse effects, and do not exacerbate the adverse CNS effects of alcohol or other CNS-active chemicals. Two H1-antagonists, astemizole and terfenadine, have been found to prolong the QTc interval and, rarely, to cause cardiac dysrhythmias after overdose or under other specific conditions. This has led to withdrawal of regulatory approval for them. An H1-antagonist absolutely free from adverse effects under all circumstances is not yet available for use.
Estelle
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F
Department of Pediatrics and Child Health, University of Manitoba, Canada.
Simons
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R
D016589:Astemizole / Q000009:adverse effects*; D002319:Cardiovascular System / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects; D006634:Histamine H1 Antagonists / Q000009:adverse effects*; D006801:Humans; D016593:Terfenadine / Q000009:adverse effects*
D006634:Histamine H1 Antagonists; D016593:Terfenadine; D016589:Astemizole