What is the Definition of OOS in pharma?

What Is The Definition Of OOS in pharmaceutical

OOS is a short form of Out of Specification in the pharmaceutical industry. In pharma, certain limits are defined for every test of the drug substance/drug product. According to that limit, results should meet criteria but if results are not within the limit or acceptance criteria then it’s considered as an Out of Specification (OOS).

As per the FDA’s guideline Investigating Out-Of-Specification (OOS) test results for pharmaceutical production

The term OOS results include all the tests that fall outside the specifications or acceptance criteria established in drug application, Drug Master File (DMF), Official compendia, or by the manufacturer.

The term also applies to all in-process laboratories tests that are outside the established specifications.

This guideline is not applicable in certain cases where in-process study solely purposes for triggering real-time equipment or system adjustment to prevent process drift.

Definition of Out Of Specification (OOS):

When the results of a drug substance or drug product fall outside the predetermined specification or defined established criteria by the manufacturer or by the laboratory then it is called Out of Specification (OOS).

OOS Investigation Example:

Let’s understand OOS with an example,

Consider, for the assay test specification acceptance criteria is 95.0% – 105.0%, then the results are observed below 95% are considered as an oos. Same the results are observed above the 105% then it is considered as an oos.

That means the results below 95% and above 105% are out of our specified acceptance criteria. In this case, the OOS lower limit is 95.0% and upper limit is 105.0%

For example: If assay result is 94.9% (i.e. below 95%) is an OOS and 105.1% (i.e. above105.0%) also an OOS.


I hope, you understand what is the definition of OOS in pharmaceuticals. If any suggestions please ping, you’re always welcome.

Definition of OOS

YT channel: Refer Pharmabeej

Refer: https://pharmabeej.com/