Some of the topics that address cleaning validation and are highlighted in the ICH Q7 document include
-Cleaning validation should be performed for process steps in which contamination
or material carryover poses the greatest risk to product quality.
-Cleaning validation should reflect actual patterns for equipment usage.
-A company should use validated methods that have the sensitivity to detect residues and contaminants.
-Equipment cleaning/sanitization studies should address microbiological and endotoxin contaminations, as appropriate.
-Cleaning validation should include monitoring of equipment at appropriate intervals to ensure that cleaning procedures are effective during routine production.
Sampling should include swabbing, rinsing, or alternate methods, as appropriate.
One of the main steps in equipment-cleaning validation is selecting the best residue detection method. There are two primary types of sampling techniques widely used in cleaning validation studies and during the routine monitoring of pharmaceutical equipment and surfaces: direct surface sampling (swabbing) and rinsing (diluent or placebo).
For bioburden recovery in cleaning validation studies, the focus is on recovery of mesophilic aerobic microbes. For this purpose, TSA medium incubated at 30–35°C is suitable. However, alternate media and incubation conditions may be required if the detection of a specified microbial species is a concern. Bacterial endotoxins are typically detected from swab and rinse samples using the Limulus amebocyte lysate (LAL) method. If swabs are used, extraction methods must be developed prior to processing the samples.
Equipment swabbing must be performed by qualified personnel, and sterile swabs made from materials that do not interfere with the test should be used. There are various types of swabs used to monitor flat or hard-to-reach surfaces such as the bottom of a tank, O-rings, traps, transfer lines, and U-bends.
Swab sampling should be carried out wearing sterile gloves to minimize adventitious contamination. For bioburden recovery, after swabbing is complete, the swab may be streaked onto an agar medium or broken into a neutralizing diluent, vortexed for about 30 seconds, and the liquid sample preparation tested by pour-plate or membrane filtration method.
The incubation conditions for the recovery media vary depending on company protocols. However, in general, swab preparations are plated with TSA and plates incubated at 30–35°C for 3–5 d. Results are reported as number of CFU per swab or area sampled. If swabs are to be transported to the testing laboratory, they need to be stored in a manner that preserves the samples collected as well as prevents adventitious contamination.
For bioburden recovery, after the rinse sample is collected, it is processed via the membrane filtration technique, the filter plated onto TSA, and the agar plate incubated at 30–35°C for 3–5 days. The use of water for equipment rinse may interfere with microbial recovery due to cell lysis. Although this topic is not addressed in cleaning validation articles and reference documents, a company should include test controls in the validation recovery studies to assess the possibility of low bioburden recovery due to loss of microbial viability.
Also, rinsing and swabbing (to a certain extent) are only partially effective in removing cells from a multilayer biofilm. Companies must consider this fact when analyzing equipment-cleaning data because microbial recovery methods may only provide a semiquantitative indication of the microbial contamination on equipment surfaces.