Tetracyclines chelate divalent cations (Ca2+, Mg2+, Al3+). Beyond reducing absorption when co-ingested with dairy/antacids, which clinical toxicity results from tetracycline's chelation of calcium in developing tissues?

• A Hypocalcemia and tetany from chronic calcium chelation
• B Permanent yellow-brown discoloration and enamel hypoplasia in teeth, and retardation of bone growth in children under 8 years and fetuses ✓
• C Renal tubular damage leading to Fanconi syndrome in adults
• D Corneal calcium deposits (band keratopathy) in infants

Explanation

Tetracyclines form stable orthophosphate chelates with calcium that are deposited in calcifying tissues including developing teeth and bones. In teeth, this causes dose-dependent yellow-brown discoloration (fluorescence under UV light) and enamel hypoplasia; in bone, the chelate can impair growth by interfering with normal mineralization. These effects are irreversible and occur predominantly when the drug is given to pregnant women, nursing mothers, or children under 8 years, hence tetracyclines are contraindicated in these groups. Fanconi syndrome can occur with outdated (degraded) tetracycline, not from calcium chelation.

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

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Written and medically reviewed by the StethoPrep medical team.