Alfalfa either ate something that she was allergic to, was envenomed by a flying insect or snake, or took a medication that she was allergic to. Diphenhydramine (Benadryl) at a dose of 1-2 mg/lb(maximum of 50 mg at any one time) repeated in 8-12 hours if necessary is appropriate. If you happen to have prednisone at home, the dose is 0.5 mg/lb repeated in 12 hours if necessary. A corticosteroid such as prednisone should be more effective in reducing the urticarial reaction (swelling/hives). As long as Alfalfa's breathing isn't labored and she appears stable - good pink color to her gums and tongue, respiratory rate ~30/minute at rest - you needn't do any more that administer the Benadryl and/or prednisone. We expect these dogs to normalize within 36 hours.
So she weighs 50 lbs, I need to give her 2 tablets (each tablet is 25mg) every 8-12 hours? What should I expect to see through the next 36 hours? She will survive if i don't take her to the emergency vet tonight?