The one-time azithromycin treatment for uncomplicated genital chlamydial infection (1 g single dose) exploits which unique PK property of azithromycin?
- A Extensive tissue accumulation (high Vd ~31 L/kg) and prolonged tissue half-life (~68 hours) ensuring sustained intracellular concentrations ✓
- B Very high plasma protein binding prolonging serum half-life
- C Complete renal excretion maintaining urinary drug levels
- D Selective concentration in hepatic bile for enterohepatic recirculation
Correct answer: A. Extensive tissue accumulation (high Vd ~31 L/kg) and prolonged tissue half-life (~68 hours) ensuring sustained intracellular concentrations
Explanation
Azithromycin has an exceptionally high volume of distribution (~31 L/kg) due to avid concentration in phagocytes, macrophages, and intracellular compartments — tissue concentrations exceed plasma levels 10-100 fold. The tissue half-life of approximately 68 hours means that a single 1 g oral dose maintains therapeutic intracellular concentrations for 7-10 days, sufficient to eradicate intracellular Chlamydia trachomatis. Plasma half-life (~40-68 h) is much longer than most macrolides.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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