A patient receiving doxycycline for scrub typhus takes the capsule with milk and an antacid containing aluminum hydroxide. Therapeutic failure occurs because:
- A Divalent and trivalent cations chelate the drug and prevent its absorption ✓
- B Gastric acid destroys doxycycline
- C Milk induces hepatic metabolism of doxycycline
- D Antacids accelerate gastric emptying, reducing contact time
Correct answer: A. Divalent and trivalent cations chelate the drug and prevent its absorption
Explanation
Tetracyclines chelate divalent and trivalent cations such as calcium, magnesium, aluminum and iron, forming insoluble complexes that are poorly absorbed. Milk products, antacids and iron supplements must be separated from doses by several hours. Doxycycline is actually the best-absorbed tetracycline and is not destroyed by gastric acid, unlike older agents. Chelation is also the basis of tooth discoloration in children, since calcium in developing teeth binds the drug.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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