APIC recently released a great guide for both API and drug manufacturers on dealing with foreign particles. The guideline differentiates between the different types of particles that can be present in a batch.
Technically unavoidable particles: particles which do not harm the health or safety of the final consumer. They should not affect the efficacy and quality of the related Drug Product due to the (chemical) harmlessness of the material and / or their mechanical attributes and low amount. Technically unavoidable particles are intrinsic to the manufacturing process, the production equipment and processing aids.
Atypical particles are particles that should not be present in final API and their presence should always trigger an investigation. These particles consist of foreign matter which is not intended/designed to be in direct contact with the product/manufacturing process. These atypical particles commonly originate from materials which accidentally or unintentionally came into contact with the product or a process stream.
The guide offers practical ways to minimize the presence of particles in APIs, proposals for limits on particle size, prevention measures, and much more.
Download the guidelines here.