The following are examples of antibiotics except:

• A. Petroleum jelly
• B. Amoxicillin
• C. Doxycycline
• D. Azithromycin

Answer: (C)

This item focuses on distinguishing antibiotics from non-antibiotic substances. An antibiotic is a drug that either kills bacteria or inhibits their growth. Amoxicillin, doxycycline, and azithromycin are all proven antibiotics with different ways of stopping bacteria: amoxicillin disrupts bacterial cell wall synthesis, doxycycline inhibits protein synthesis by targeting the 30S ribosome, and azithromycin also inhibits protein synthesis but at the 50S ribosome. Petroleum jelly, in contrast, is a barrier ointment used to protect and moisturize skin; it has no antibacterial action. Because of that, petroleum jelly is the one that is not an antibiotic.