Has anyone else gotten Convenia for skin/abscess conditions?

A stray cat I'm caring for was given a shot of Convenia for one ear abcess and a slight neck wound 5 days ago. He was also neutered at that time. The shot did work for him fortunately, the healing of his skin is on track. Although the side effects: including extreme lethargy, decreased appetite and diarrhea or soft feces are increasing and becoming extremely concerning. I love the idea of no mess, one simple injection that lasts two weeks. This is one of best advance in Vet science for years…there just wasn't a warning to watch to make sure he seemed to be getting better and not worse.

Has anyone has similar experiences with side effects to this antibiotic ?