My Nearly 11 Year Old Poodle Was Diagnosed With Kennel

my nearly 11 year old poodle was diagnosed with kennel cough today. He was given azithromycin oral suspension. First dose was at 2:30 p.m. Fine all afternoon, ate dinner about 5:00, started to show discomfort about 7:40 and vomited his dinner at 8:00. Then drank water and vomited that. He is now resting comfortably. I will call his vet in the morning, but do you feel the time between taking dose and vomiting (about 5 hours) gave the first does a chance to work? Should medicine be discontinued ($37) or just be sure to feed first and then give the dose?