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US FDA have not mentioned specification or limits or methods cleaning and for residue after cleaning of equipments and its parts, as there are lot of variations in equipment designs and drug products to determine if the cleaning process is validated or not. Establishing the limit for residue after cleaning of equipments should be logical, it should be practical and achievable based on knowledge of chemistry of residue and it should be verifiable.
Some pharmaceutical industry representatives do mention limits for residue after cleaning of equipments as 10 PPM for analytical detection level and for biological activity level as 1/1000 of the normal therapeutic dose of the drug in the residue, and organoleptic limit as no visible residues after cleaning. The residue of the detergent used must be absent or to a very low level only detectable in minute quantity in ultra low detection methods
The sensitivity of the method used for detection and estimation of residue after cleaning should be capable to achieve the detection determinations and estimation of residues to the set limits level.
The drug residues may be from intermediates and byproducts may skip the regular method of detection hence complete screening of intermediates of drug products must be done, while setting up the limits.
TLC screening of the residue sample do provide good method for finding out the residue after cleaning, it is of great importance in case of steroidal drug products where very micro level of steroidal drugs contamination should be avoided.
