Chloramphenicol starts working in your pet after the first several hours. Antibiotics can take time to bring infections under control before you can observe an improvement in symptoms. Make sure to communicate with your vet if you do not notice any improvement over the course of the first week. No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer. Featured Image: iStock.com/Zbynek Pospisil