A 40-year-old man taking ciprofloxacin for urinary infection asks whether he may take his calcium carbonate supplement with each dose. You should advise him to separate the doses because coadministration will:

• A Accelerate renal clearance of ciprofloxacin by alkalinizing urine
• B Induce hepatic metabolism of ciprofloxacin via CYP1A2
• C Increase the risk of tendon rupture through calcium overload
• D Chelate the drug in the gut and markedly reduce its absorption ✓

Explanation

Fluoroquinolones chelate divalent and trivalent cations including calcium, magnesium, aluminum, iron, and zinc within the intestinal lumen, forming insoluble complexes that drastically reduce oral bioavailability. Doses should be separated by several hours. Urinary alkalinization does not meaningfully increase quinolone clearance, and tendon injury is unrelated to concurrent calcium intake. Ciprofloxacin inhibits CYP1A2 rather than inducing it.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.