A 25-year-old woman is prescribed doxycycline for pelvic inflammatory disease. Which mechanism explains why tetracyclines should be avoided in pregnancy?
- A Tetracyclines inhibit placental lactogen, causing fetal growth restriction
- B Tetracyclines chelate calcium and deposit in developing bone and teeth, causing permanent yellow discolouration and inhibiting bone growth ✓
- C Tetracyclines cause fetal kernicterus by displacing bilirubin from albumin
- D Tetracyclines block fetal renal tubular secretion of uric acid, causing hyperuricaemia
Correct answer: B. Tetracyclines chelate calcium and deposit in developing bone and teeth, causing permanent yellow discolouration and inhibiting bone growth
Explanation
Tetracyclines chelate calcium ions and deposit in mineralising bone and enamel, causing permanent yellow-brown tooth staining (fluorescent under UV) and reduced bone growth in fetuses and children under 8 years. They cross the placenta freely and enter breast milk. Kernicterus by albumin displacement is a risk of sulphonamides (not tetracyclines). This calcium chelation is also the basis of their interaction with dairy products and antacids.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.