Jp. Corey, ADVANCES IN THE PHARMACOTHERAPY OF ALLERGIC RHINITIS - 2ND-GENERATIONH1-RECEPTOR ANTAGONISTS, Otolaryngology and head and neck surgery, 109(3), 1993, pp. 584-592
Allergic rhinitis, whether seasonal or perennial, potentially affects
up to 30% of the population. Pharmacotherapy for allergic rhinitis tha
t is directed at symptomatic relief traditionally includes antihistami
nes as one of the first lines of therapy. All antihistamines are H-1-r
eceptor antagonists, or H-1 blockers; they are reversible, competitive
inhibitors of the actions of histamine, a critical mediator in the pa
thophysiology of the allergic response. Nearly all antihistamines (wit
h the exception of the second-generation antihistamine cetirizine) are
metabolized by the hepatic cytochrome P-450 system. Potentially fatal
adverse effects of antihistamines may include heart arrhythmias from
overdosage. Hepatic or cardiac dysfunction also predisposes to heart a
rrhythmias in patients who take antihistamines. Concomitant administra
tion of macrolide antibiotics or antifungal agents with antihistamines
may also predispose patients to potentially fatal heart arrhythmias.
First-generation H-1 blockers (e.g., the ethanolamines, ethylenediamin
es, alkylamines, piperazines, and phenothiazines) offer rapid relief o
f symptoms (usually within 15 or 30 minutes) but have the potential fo
r significant sedation and for adverse reactions and drug interactions
, as previously described. In contrast, however, the second-generation
H-1-antagonists (e.g., clemastine, terfenadine, astemizole, acrivasti
ne, loratadine, and cetirizine) offer equal or superior relief but hav
e markedly decreased sedation potential. This article compares first-
and second-generation H-1 blockers to provide clinicians with a better
understanding of each agent's actions, potential side effects, and ef
ficacy as antihistamine therapy.