Diphenoxylate is a structural analog of ________ which is chemically a ________.

• A. Meperidine; phenylpiperidine
• B. Pethidine; pyridine
• C. Methadone; phenylheptylamine
• D. Pentazocine; benzomorphan

Answer: (A)

Diphenoxylate is built on the same chemical scaffold as certain opioid analgesics, sharing the phenylpiperidine framework. Meperidine (also called pethidine) is a classic opioid whose core structure is a phenylpiperidine. Because diphenoxylate mirrors that same core, it’s best described as a structural analog of meperidine, which is chemically a phenylpiperidine. That’s why the pairing meperidine with phenylpiperidine is the correct choice.

The other options mix in different chemical families—methadone has a phenylheptylamine backbone, pentazocine is a benzomorphan, and while pethidine is another name for meperidine, it would be incorrect to describe it as pyridine, since the correct ring is piperidine, not pyridine.