Why are most antibiotics contraindicated in rabbits and hamsters?

Antibiotics are often contraindicated in rabbits and hamsters primarily because they can disrupt the gram-positive gut flora that is essential for their digestive health. Rabbits and hamsters are hindgut fermenters, meaning they rely heavily on a specific balance of microorganisms in their gastrointestinal tract to aid in digestion. The normal flora is predominantly composed of gram-positive bacteria, which help break down fibrous plant material.

When antibiotics that target a broad range of bacteria or specifically those that are effective against gram-positive bacteria are administered, they can lead to a significant imbalance in the gut microbiome. This disruption can result in serious gastrointestinal issues, such as diarrhea, dysbiosis, and potentially life-threatening conditions like enterotoxemia. Maintaining the integrity of the gut flora is crucial for these animals' health, making the careful selection of medications vital in veterinary practice.