Effect of milk on effectiveness of oral tetracycline?

Question

Tetracycline is known to be inhibited by calcium ions, and milk contains quite some calcium ions. What I want to ask is, to what extent does drinking milk affect the effectiveness of orally taken tetracycline?

Answer 1

Dairy products or supplements containing calcium should not be taken within 2 hours of tetracycline because the calcium and the tetracycline molecules will chelate or bond together to form a molecule that is too large to be absorbed from the GI tract, therefore less of it will get into the bloodstream. It's absorption can be reduced by 50-90% in this way, which is significant. If the drug can't be absorbed into the bloodstream, then it can't get to where it needs to go to do its job. This same chelation interaction can also occur between tetracycline and iron, magnesium and aluminum, so we recommend separating tetracycline from dairy products and also from supplements or antacids that contain these elements.