Why are tetracyclines avoided in young animals and during pregnancy?

• A. They cause severe GI upset in all ages
• B. They chelate calcium and deposit in developing teeth and bones, causing discoloration and growth impairment
• C. They interact with vaccines
• D. They cause liver injury

Answer: (B)

Tetracyclines are avoided in young animals and during pregnancy because they bind calcium and other divalent ions, forming chelates that are incorporated into developing teeth and bones. As teeth and bone are actively mineralizing, the drug accumulates in dentin and enamel, leading to permanent discoloration of teeth and enamel hypoplasia, and it can interfere with normal bone growth. These effects are lasting because the tissues are still forming, so exposure during development produces lasting changes. Additionally, tetracyclines can cross the placenta and are excreted into milk, exposing the fetus or nursing offspring to the drug. For these reasons, safer alternatives are preferred in pregnant animals and young, growing animals.