Do antihistamines make allergies worse?

[Guest guest]

1 January 2008 | Nature | doi:10.1038/news.2008.436

Do antihistamines make allergies worse?

Medicated mice react more to bee stings than non-medicated mates.

Matt Kaplan

http://www.nature.com/news/2008/080111/full/news.2008.436.html

Taking antihistamines can be a great way to fight off an allergic

attack. But new research suggests it also might also make the next

attack come on stronger.

Allergies are immune reactions to foreign substances that normally pose

no threat to the body, from peanuts to pollen, that can set in after

repeated exposure. In theory, even if someone has a genetic

predisposition to react to peanuts, they should not react to the first

peanut they encounter: it's the second one that they need worry about.

Antihistamines, with their ability to disrupt the immune response that

leads to annoying reactions like runny noses and swelling tissues, have

long been considered the ideal way to control allergies. But their

long-term effects on the immune system are unknown.

To explore this, a team led by Pål Johansen at the University of Zurich,

Switzerland studied 50 mice that were initially injected with bee venom,

a substance that nearly all organisms develop an allergy to upon

exposure. Half of the mice were also given 100 micrograms of the

antihistamine Clemastine just before they were given venom and 100

micrograms on each of the two days afterwards.

Six weeks later Johansen and his team injected the mice with another

dosage of bee venom and monitored the allergic reactions. They report in

Clinical and Experimental Allergy ^1

<http://www.nature.com/news/2008/080111/full/news.2008.436.html#B1> that

mice given antihistamines reacted more violently to the second venom

injection.

Going up, going down

" We believe that the antihistamines were doing more than disrupting the

immediate immune reaction to the first venom dosage, " says Johansen. " We

think they were also keeping the immune system from getting used to that

dosage. " That means the mice on allergy medication had no chance to

build up a tolerance to the allergen.

In a second part of the study, Johansen's team desensitized the mice to

the bee venom using immunotherapy --- a process of introducing tiny

amounts of an allergenic substance to an allergic individual, slowly

helping the immune system to tolerate the substance (in this case they

used one-third of the bee venom dose used to provoke a reaction). Unlike

antihistamines, immunotherapy can permanently change the way the body

responds to a substance and cure allergies.

Mice that had originally been on antihistamines when sensitized with

venom responded more poorly to the immunotherapy than the other mice.

" This was really surprising because others^2

<http://www.nature.com/news/2008/080111/full/news.2008.436.html#B2> ^,

^3 <http://www.nature.com/news/2008/080111/full/news.2008.436.html#B3>

have claimed that antihistamines would aid the process of immunotherapy,

and that is simply not what we saw, " says Johansen.

Rodent test

Such work is important for understanding how the immune system interacts

with antihistamines, says Katz, an allergist at the University of

California School of Medicine, Los Angeles. But, he adds, " there is a

problem of mice and men " .

Human immunotherapy is typically done over the course of months or

years, not weeks, says Katz. And the mice in this study were given a lot

of Clemastine for their weight. If they happen to metabolize the

antihistamine more slowly than people, this could lead to drug

accumulation, which could affect immune system function and potentially

explain the study results, says Katz.

But there is no evidence that rodents and people metabolize Clemastine

at different rates, says Cezmi Akdis, director of the Swiss Institute of

Allergy and Asthma Research in Davos, Switzerland. Antihistamines were

originally tested on rodents before being used on humans, he adds, and

there have been decades of research on medication in these animals.

Only two studies suggest antihistamines help immunotherapy, and this is

the first to contradict them, says Akdis. " We definitely need more

research in this area, " he says.

*

References

1. Johansen, P. /et al./ Clin. Exp. Allergy DOI

10.1111/j.1365-2222.2007.02904.x (2008)

2. Ohashi, Y., Nakai, Y. & Murata, K. Ann. Allergy Asthma

Immunol. 96, 600-605 (2006) | PubMed

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg & cmd=Retrieve & db=PubMe\

d & list_uids=16680932 & dopt=Abstract> |

3. Müller, U., Hari, Y. & Berchtold, E. J. Allergy Clin.

Immunol. 107, 81-86 (2001) | Article

<http://dx.doi.org/10.1067/mai.2001.111852> | PubMed

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg & cmd=Retrieve & db=PubMe\

d & list_uids=11149995 & dopt=Abstract> |

Comments

*

The material in this post is distributed without

profit to those who have expressed a prior interest

in receiving the included information for research

and educational purposes.For more information go to:

http://www4.law.cornell.edu/uscode/17/107.html

http://oregon.uoregon.edu/~csundt/documents.htm

If you wish to use copyrighted material from this

email for purposes that go beyond 'fair use', you

must obtain permission from the copyright owner*.*