Tetracycline Interactions

Calcium binds tightly to tetracycline in the gut, forming an insoluble chelate that cannot be absorbed. Dairy products and calcium supplements can reduce tetracycline absorption by 50 to 90 percent, often dropping serum levels below the threshold needed to treat infection.

Zinc forms a chelate with tetracycline in the gastrointestinal tract, reducing absorption of the antibiotic by approximately 30 percent. The interaction also reduces zinc absorption.