Normally a reaction to penecillin would happen within the first 15 minutes of giving it to the ferret. Anaphylaxis is what the reaction is called and is fairly rare. Usually, the t ferret will start shaking within 10 or 15 minutes after the vaccine, and it may vomit or have diarrhea on the exam table, and the gums will quickly become very pale and the pet will collapse. It will quickly become unresponsive.