Kennel cough involves several viruses and only one bacteria, Bordetella bronchiseptica, which the lab probably will not culture because it is difficult to grow. So antibiotics will not "cure" it.
Treatment requires time (about 2 weeks) and a good immune system. We do use an antibiotic called Zithromax in many of these cases to kill the Bordetella. We also use oral steroids to reduce the inflammation in the trachea and bronchi and a drug called Torbutrol to decrease the cough reflex in the brain. Ask your vet about these suggestions.
If he is vomiting, do not feed him for 12 hours to let his stomach rest. If he is vomiting on an empty stomach, he may need an injection to settle his stomach.
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Dr. Louis Gotthelf
Animal Hospital of Montgomery
Pet Skin and Ear Clinic