How can antacids reduce the absorption of tetracycline?

Antacids can reduce the absorption of tetracycline because they often contain minerals such as calcium, magnesium, or aluminum.1

These minerals interact with tetracycline to form insoluble products, a process related to the formation of a chelate—a stable complex where a metal ion is bound to a molecule. Because these resulting complexes are insoluble, they cannot be effectively absorbed from the gastrointestinal tract into the bloodstream. Consequently, to ensure the medication remains effective, tetracycline should not be taken simultaneously with substances containing these minerals.12