24 hours: Alavert is approved as a once daily antihistamine.
Answered 9/28/2016
6.4k views
Variable: It all depends. What were the allergic symptoms....Skin, breathing, GI tract, cardiac. Usually an allergic reaction can be between 2 hours to 7 days based on the reaction and many other factors.
Answered 6/10/2014
5.5k views
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