In inflammatory bowel disease (IBD), an allergic reaction in the walls of the intestines causes inflammation that interferes with the normal function of the gastro-intestinal system. Treatment centers around removing the cause of the allergic reaction and suppressing the immune system. In addition, some veterinarians like to add a broad spectrum antibiotic to the treatment plan. This protects against a bacterial infection when the cat is receiving steroids to suppress the immune system. Since bacterial overgrowth is not commonly associated with inflammatory bowel disease, other veterinarians disagree with this approach because indiscriminate use of antibiotics may lead to bacterial resistance.
When I treat a patient for inflammatory bowel disease, I let the blood work and the patient’s temperature tell me if they need antibiotics. If the patient has a high white blood cell count primarily from neutrophils and/or is febrile, I know the intestinal mucosa has suffered severe damage allowing bacteria to enter the blood stream. I treat these cats with a broad spectrum antibiotic but warn the owners that some antibiotics can cause gastrointestinal upset. After two weeks of therapy, I stop the antibiotics and then consider probiotics to restore the normal gut flora.
Lastly, I would like to clear-up confusion about metronidazole use in IBD. This drug is an antiprotozoal which means it kills protozoal organisms such as giardia. It also is a great antibiotic for anaerobic bacteria. But it is used in inflammatory bowel disease for its ability to inhibit cell-mediated immunity which decreases the inflammation in the mucosa.