Tetracyclines chelate polyvalent cations. The major clinical implication of this property is:

• A They increase serum magnesium by chelating dietary phosphate
• B They require co-administration of calcium supplements to maintain antibacterial effect
• C They can chelate calcium in bone and deciduous teeth, causing permanent dental staining in children under 8 years ✓
• D Chelation of zinc in bacterial ribosomes is the primary antibacterial mechanism

Explanation

Tetracyclines have a high affinity for polyvalent cations (Ca2+, Mg2+, Fe3+, Al3+). When administered during tooth development (in utero through age 8), tetracyclines chelate calcium in the hydroxyapatite of enamel and dentin, forming a permanent yellow-brown discoloration (tetracycline staining) that cannot be reversed. They also chelate calcium in developing bone, causing temporary growth retardation. This is why tetracyclines (doxycycline, minocycline, etc.) are absolutely contraindicated in children under 8 years and in pregnant/lactating women. Co-administration of dairy products, antacids, or iron supplements also reduces tetracycline absorption by approximately 50-90% via the same chelation mechanism.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.