Antihistamines Increase Repeated Reactions to Bee Venom

Do Antihistamines Make Allergies Worse?
Medicated mice react more to bee stings than non-medicated mates
Matt Kaplan, Nature News, 1/11/2008

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 that mice given antihistamines reacted more violently to the second venom injection…