A patient is prescribed antibiotics and should avoid taking with iron within two hours before or after a dose. Which antibiotic requires this warning?

• A. Amoxicillin
• B. Ciprofloxacin
• C. Doxycycline
• D. Azithromycin

Answer: (C)

The key idea is that certain antibiotics form chelates with minerals like iron in the gut, which prevents them from being absorbed effectively. Doxycycline, a tetracycline, is especially prone to this interaction. When iron is taken within two hours of a doxycycline dose, iron binds the drug in the gastrointestinal tract and creates insoluble complexes. This dramatically reduces doxycycline’s absorption, lowers systemic exposure, and can compromise its antibacterial effect. Therefore, the guidance is to avoid taking iron within two hours before or after a doxycycline dose.

The other antibiotics listed don’t have this interaction as a primary concern in the same way. Amoxicillin’s absorption isn’t significantly affected by iron; azithromycin is not notably inhibited by iron in typical dosing; ciprofloxacin can have interactions with divalent cations as well, but the classic and most emphasized warning for mineral separation is associated with doxycycline.