Which drug class is commonly affected by chelation with antacids, reducing absorption?

• A. Tetracyclines
• B. Beta blockers
• C. Statins
• D. Opioids

Answer: (A)

Chelation with multivalent cations in antacids reduces absorption of tetracyclines. Tetracyclines readily bind calcium, magnesium, and aluminum ions found in antacids (and dairy in some cases) to form insoluble complexes in the gut, which cannot be absorbed. This lowers the drug’s bioavailability and systemic exposure. Clinically, separate antacid use from tetracycline dosing by several hours and take the antibiotic with water on an empty stomach when possible. Other drug classes listed do not form significant chelates with common antacids, so their absorption isn’t markedly reduced by this interaction.