Azithromycin's pharmacokinetic property that allows a 3-day or 5-day course to be therapeutically equivalent to 10-day amoxicillin is its:
- A Extraordinary tissue concentration (volume of distribution ~31 L/kg) with slow release from tissues giving prolonged tissue levels ✓
- B Extended post-antibiotic effect due to tight ribosomal binding without tissue distribution
- C CYP3A4 induction increasing its own metabolic activation to a more potent bactericidal form
- D Renal tubular secretion concentrating it at urinary sites of infection
Correct answer: A. Extraordinary tissue concentration (volume of distribution ~31 L/kg) with slow release from tissues giving prolonged tissue levels
Explanation
Azithromycin has an unusually large volume of distribution (~31 L/kg) because it concentrates extensively in tissue and intracellularly, particularly in phagocytes (macrophages, neutrophils). It is actively transported into tissues via organic cation transporters, reaching tissue-to-plasma ratios of 10–100:1. This depot effect means that even after the serum level falls below MIC, tissue concentrations remain bacteriostatic for up to 5–7 days post-dosing. This pharmacokinetic property allows abbreviated dosing regimens.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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