What is the difference between an intermediate and an API?

First, let's take a look at the definition of intermediate and API in Q7A of ICH.

Intermediate

A material produced in the process that must undergo further molecular modification or refinement to become an active drug substance. The intermediate may or may not be separated. (Note: This guidance relates only to intermediates manufactured after the company defines them as the starting point for API manufacturing.)

Active Pharmaceutical Ingredient (API)(or Drug Substance) 

API is intended to be used by any substance or mixture of substances in the manufacture of pharmaceutical products and, when used in pharmaceutical products, as an active ingredient in pharmaceutical products. The substance has pharmacological activity or other direct effect in the diagnosis, treatment, symptom relief, management or prevention of disease, or can affect the function and structure of the body.

As can be seen from the definition, intermediates are the key products of the previous process of making an API and have a different structure from the API. In addition, the pharmacopoeia has testing methods for bulk drugs, but not for intermediates.

For example

Amoxicillin capsules is called preparation, amoxicillin is called API, 6-APA is called intermediate.

Ceftriaxone sodium powder is called preparation, sterile ceftriaxone sodium is called API, 7-ACA is called intermediate.