Good thing you reacted so quickly and thanks for the heads up!
I would ask the vet what would be good to have on hand for him should it happen again. Maybe he can write a script for Epi pens for him.
Anaphylaxis in Dogs: Severe Acute Allergic Reactions
For animals that are allergic to insect bites, such as bees, ask your veterinarian about getting a prescription for an 'epi-pen' and be sure to take the 'epi-pen' with you on any trips or hikes. An 'epi-pen' is a special syringe and needle filled with a single dose of epinephrine. If your pet has an anaphylactic reaction, inject the epinephrine using the 'epi-pen' and seek emergency veterinary assistance immediately