What's the antibiotic? It sounds like metronidazole, a notorious spit-foam-slobber antibiotic. If so, your best bet may be to talk to other rescuers and find out who the best pharmacist is in your area for flavoring kitty meds. Many don't bother, and most of the others don't have a clue how to do it effectively. The best pharmacist for kitty meds in our area practiced on his own kitty and those of rescuers until he got the recipe perfect.