Which antibiotic pair represents penicillins that share the same core structure but differ in side chains among the options?

• A. Amoxicillin and Ampicillin
• B. Penicillin G and Penicillin V
• C. Oxacillin and Nafcillin
• D. Dicloxacillin and Flucloxacillin

Answer: (A)

Penicillins share a common beta-lactam core structure, and the diversity among them comes from the side chains attached to that core. Amoxicillin and ampicillin are both aminopenicillins that originate from the same core scaffold, with their side chains differing only in that attachment. This means their core chemistry is essentially the same, while the side-chain variation tweaks properties like spectrum and pharmacokinetics without changing the fundamental nucleus. Other pairs also differ in side chains, but the standout example of retaining the same core while showing a straightforward side-chain modification is the ampicillin–amoxicillin pair, illustrating how side-chain changes can occur on an identical core.