Doxycycline is preferred over older tetracyclines (oxytetracycline) in patients with renal impairment because:

• A Doxycycline does not chelate divalent cations in the GI tract
• B Doxycycline is primarily excreted via bile/faeces, avoiding accumulation in renal failure ✓
• C Doxycycline undergoes renal tubular secretion, maintaining therapeutic urinary levels
• D Doxycycline is metabolised by CYP3A4 to inactive products regardless of renal function

Explanation

Unlike other tetracyclines that are primarily renally excreted and accumulate in renal failure (worsening azotaemia due to anti-anabolic effects), doxycycline is excreted mainly via the bile into faeces (as inactive conjugates). Its plasma half-life remains approximately 18-22 hours even in advanced renal failure, making it safe without dose adjustment. All tetracyclines chelate divalent cations — this is a class property, not unique to doxycycline.

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

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Written and medically reviewed by the StethoPrep medical team.