Febuxostat is used for hyperuricemia in gout. Unlike allopurinol, febuxostat selectively inhibits xanthine oxidase without inhibiting other purine-metabolizing enzymes. What is the MAIN pharmacokinetic advantage of febuxostat in patients with mild-to-moderate renal impairment?

• A Febuxostat undergoes complete renal elimination, reducing accumulation in liver disease
• B Febuxostat is a prodrug converted to active form only in renal tubular cells
• C Febuxostat is metabolized primarily by hepatic conjugation (UGT and CYP) with both renal and biliary/fecal excretion, requiring less dose adjustment in renal impairment compared to allopurinol's renally-excreted active metabolite oxypurinol ✓
• D Febuxostat is renally cleared unchanged, making it safer in hepatic failure

Explanation

Allopurinol is converted to its active metabolite oxypurinol, which is renally eliminated with a long half-life; in renal impairment, oxypurinol accumulates, increasing the risk of severe hypersensitivity reactions (allopurinol hypersensitivity syndrome). Febuxostat is primarily metabolized by hepatic oxidation (CYP1A2, CYP2C8, CYP2C9) and glucuronidation (UGT), with both renal (~49%) and biliary/fecal (~45%) excretion. This dual elimination means dose adjustment is not required for mild-to-moderate CKD (eGFR >30 mL/min), making it safer in renal impairment. Febuxostat is not a prodrug and is not cleared unchanged renally.

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

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