### Question
How is the "isomer" defined?


### Answer
The term **isomer** is defined in *21 CFR § 1300.01* as follows -

> the optical isomer, except as used in § 1308.11(d) and § 1308.12(b)(4) of this chapter. 

#### Citation:
  - *21 CFR § 1300.01*
  - Heading: **PART 1300—DEFINITIONS > PART 1300—DEFINITIONS**

