Described herein are injectable compositions containing non-sedating or second and third generation antihistamines such as cetirizine/levocetirizine and methods of use thereof. Specifically, methods of treating acute allergic reactions including anaphylaxis with the compositions are disclosed. In certain embodiments, the injectable compositions are bioequivalent to currently marketed oral dosage forms. In other embodiments, the non-sedating or second and third generation antihistamine injectable formulations are therapeutically equivalent to diphenhydramine injectable formulations and/or are more effective than placebo. In other embodiments, a non-sedating antihistamine injectable composition is delivered by an autoinjector.