Doxycycline, a semi-synthetic tetracycline, has broader clinical utility than older tetracyclines. Which property specifically explains its utility in treating Chlamydia trachomatis and Rickettsia infections that are obligate intracellular organisms?

• A Doxycycline is lipophilic with high intracellular penetration and concentrates within macrophages and epithelial cells where obligate intracellular bacteria reside ✓
• B Doxycycline is actively transported into host cells by the bacterial TRAP transporter, concentrating inside infected cells
• C Doxycycline inhibits ATP synthesis in host mitochondria, depriving intracellular bacteria of energy
• D Doxycycline disrupts the bacterial outer membrane of Gram-negative obligate intracellular pathogens

Explanation

Doxycycline has greater lipophilicity than tetracycline, allowing it to penetrate cell membranes and accumulate within phagolysosomes of macrophages and other host cells. This intracellular concentration is essential for reaching obligate intracellular pathogens like Chlamydia, Rickettsia, and Coxiella, which cannot be targeted by hydrophilic drugs. Intracellular accumulation combined with its broad spectrum accounts for its use as first-line therapy in these infections.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.