The correct answer is Doxycycline.

- Certain antibiotics, particularly those in the tetracycline class such as doxycycline, have their absorption significantly decreased when taken concurrently with dairy products.
- This is because dairy products contain calcium ions which can form chelation complexes with doxycycline, resulting in reduced bioavailability of the drug.
- This interaction impairs the drug's effective plasma concentration and thus decreases its therapeutic efficacy.

- In contrast, other antibiotics like azithromycin and amoxicillin are not significantly affected by dairy products.
- Ciprofloxacin, another antibiotic known to form chelates with divalent cations, is affected by dairy, but its interaction is less pronounced compared to doxycycline and often emphasized with supplements containing calcium, magnesium, or iron rather than dairy alone.

Key points:
- Doxycycline's absorption is decreased due to chelation with calcium in dairy.
- Always avoid taking doxycycline with milk, cheese, or other dairy products.
- Other antibiotics listed do not exhibit clinically significant absorption issues with dairy.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th Edition, Antibiotics Chapter/Page 1058-1060