Compression machine dies and punches are most critical for cleaning validation purposes for several reasons:
Let’s review what happens in a typical multi-station rotary press. Everything is contained in an upper polycarbonate chamber (to prevent dust from escaping as well as to prevent dusts from the environment potentially contaminating processed tablets). The heart of the tablet press are the die cavities (which contain the loose powder for proper tablet weight) and the lower and upper punches. The lower punch provides the floor of the die cavity so that the die can be filled with the proper amount of powder. There is a powder hopper (which serves as a reservoir for powder) and a feeder which feeds product into the die cavity (thereby controlling amount of powder in the die). The excess powder is scraped off and recycled into the hopper. The upper punch then compresses the powder into a tablet, and then the lower punch rises to eject the tablet. A take-off mechanism directs the tablet to the collection chute that takes tablets to the collection bin.
Dies and punches
Typically the dies and punches are dedicated to one drug product. This simplifies the handling of these parts for cleaning validation purpose. That is, after cleaning, the dies and punches only see the same product. In this case for the dies and punches, the main cleaning validation requirement for chemical residues generally is that those tools be visually clean. Testing for microorganisms may not be required if the tooling is given a final rinse with alcohol.
For cleaning, the dies and punches are removed from the press, with cleaning done elsewhere. The cleaning process may be fully manual or in an ultrasonic tank. In either case, the cleaning process typically involves a preflush with water to remove loose product, a wash with a mildly alkaline detergent solution, and multiple water rinses (WFI or PW), followed by an alcohol rinse. The alcohol rinse helps ensure that trace water is not left on the surfaces (thus minimizing corrosion before next use), as well as reducing microorganisms on the cleaned tooling. The cleaned tools are stored in a controlled manner to minimize external contamination before next use.
Other product contact surfaces
Other items that will contact product (either the powder or tablets) include the feed frame (generally not removed), the scraper blade (may be removed depending on design), the take-off mechanism (may be removed depending on design), the discharge chute (typically removed) and the collection bin (definitely removed). For items removed, the cleaning process may be similar to cleaning process for dies/punches, or it may just involve a combination of brushing, vacuuming and/or wiping. Since these items do not involve product as it is being compressed, the cleaning process may be less stringent, but they still should be part of a validated cleaning process since they are product contact parts.
Non-product contact surfaces
Non-product contact surfaces within the primary chamber should be cleaned on a defined schedule. For clarification, product dusts may contact these surfaces, but generally those “dusts” are the same product being processed into tablets (and are not a cross-contamination risk). So the key for cross-contamination is the changeover from one product to a different product. Either at changeover or within a campaign of the same product, cleaning processes are similar to product surfaces not removed (discussed above), involving some combination of brushing, vacuuming and/or wiping. Within a campaign the defined frequency will be established by the facility, and may be after a shift change or at a daily shutdown. During this type of cleaning for the non-product contact parts, the same type cleaning may be done for product-contact items. For such cleaning within a campaign, the concern is not so much cross-contamination but rather production efficiency and/or product quality. For example, do dusts build up such that picking occurs, impacting the physical appearance of the tablets.
Setting residue limits for product contact surfaces
This requires careful assessment. A key issue is to what extent the direct transfer of residues from equipment surfaces is such that the residue appears more or less uniformly in the processed batch. The worst-case scenario (resulting in lowest residue limit) is to include the surface area of those direct product contact surfaces in an overall (that is, cumulative) carryover residue limit for the processed batch. An alternative hypothesis is that transfer of residue mainly occurs to an initial portion of tablets processed. If the latter is the case, then cross-contamination risks are significantly reduced since an initial number of tablets is typically discarded before tablets meeting QC specifications are consistently produced. This will depend on the facility and equipment and the tablet formulation, and may be several revolutions of the turret. In calculating such transfer for the initially processed tablets, it must be recognized that the surface area of the die/punches to product weight ratio will be much higher than similar ratio calculation for earlier process steps (such as granulation).
Other factors to consider to deal with this alternative hypothesis include whether migration of the lubricant (such as magnesium stearate) to the outside of the tablet due to high pressures affects any transfer from the surface to the outside of the tablet. Furthermore, residues transferred to the to the outside of the tablet during compression may be removed as the tablet is further processed on the discharge chute or on a conveyor belt. I have not seen any definitive studies investigating this, but these consideration certainly suggest a lower the risk of cross-contamination. If you want to address the issue of preferential transfer by either establishing that it does not occur to any significant extent and/or to justify how much of an initially processed batch should be discarded, the January 2025 Cleaning Memo has several options for types of approach to evaluate cleaning limits at a product changeover. For cleaning within a campaign, a formal validation study may not be required, but the cleaning should be documented and, at a minimum.
While this Memo focuses on limits for the tableting equipment, cumulative transfer from all product contact surfaces must be considered to account for all sources of residues.
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