When running manufacturing equipment continuously, rather than in batch mode, operators should consider what cleaning practices need to be adjusted. FDA’s draft guidance for continuous manufacturing of small-molecule, solid oral drug products notes time between equipment cleanings can depend on a variety of factors, such as running time or amount of product (1).

When considering equipment running continuously, cleaning might be automated with clean-in-place (CIP) elements or involve full disassembly with manual cleaning, say Paul Lopolito, senior manager, and Beth Kroeger, senior manager, in Technical Services at STERIS. “Using cleaning agents or cleaning tools requires a cleaning validation to demonstrate removal of these elements to acceptable limits. The calculation of accepted limits may utilize traditional uniform carry-over models or non-uniform residue or stratified residue models,” say Lopolito and Kroeger. These models are used because residue can become concentrated as it moves through the connected equipment (2). Other considerations with continuous manufacturing are addressing microbial issues and process intermediate degradant residue. “These residues may present a cross-contamination risk to the next lot or batch of product. If these hazards exist, then it is warranted to perform the appropriate level of cleaning and cleaning validation to mitigate the risk,” they conclude.

Most lines for continuous manufacturing of solid-dosage drugs today are cleaned in a “clean-out-of-place” mode, but a complete CIP solution would improve cleaning turnaround times, notes José Luís Santos, director of Hovione’s Continuous Tableting Center of Excellence, who suggests that end-users would need to work closely with equipment vendors to develop such a system for a full process train. Hovione’s contract development and manufacturing facility in New Jersey has been running continuous solid-dosage drug manufacturing equipment for a few years and working to streamline the manual cleaning process.

“The magnitude of the task of changing over a continuous manufacturing rig from one product to the next is very large,” explains Santos. “From a unit operation standpoint, there are no major differences from batch equipment, and in most cases the equipment is exactly the same at the unit operation level. The differences between continuous and batch have to do with the transition sections in between [the integrated] unit operations. Depending on the actual setup of the continuous rig, these transitions can be comprised of large pipe sections, in some cases with pass-through connections between floors. Also, such transitions might comprise large number of PAT instruments to measure, for example, powder level or quality attributes of the material being processed. Thus, continuous rigs have additional parts to be cleaned. If the continuous manufacturing line is entirely ‘clean-out-of-place,’ the extra equipment also poses the added challenge of keeping track of many equipment components of all different sizes as they move through the cleaning operation and subsequent reassembly; the learning curve associated with these operations may be much longer than comparable operations of individual batch manufacturing units.”

Santos notes that, “While in batch, each unit operation is operated independently, in separate rooms, and typically staggered in time; in continuous, the full set of equipment is used during manufacturing, typically with higher asset utilization. Hence, from a planning standpoint, the cleaning of continuous rigs requires significantly more resources, effort, and cleaning capacity (e.g., additional wash rooms and footprint for parts staging and storage) to address the full set of equipment without impacting productivity of the area or overall equipment effectiveness (OEE).”

A cleaning best practice applied at Hovione was to allocate enough resources to address the manual cleaning process—including a large team of operators and enough space to do the cleaning—and then to optimize with shop-floor operational excellence tools, says Santos. “In our experience, the use of Lean [management tools] brought not just the acceleration of the operation, but also an increase of the comfort levels of the team members involved with the cleaning. An otherwise huge challenge could be decomposed into smaller, more manageable, blocks of work, with a clear visibility of how the work was progressing during each day of the operation,” he explains.

Another best practice is to maintain control of the organization of equipment components from disassembly through assembly. “For example, use specific bins to contain disassembled components from specific (predefined) sections of the line so that those components, which make up those specific line segments, stay together throughout the cleaning process. Organization is critical to reduce lost and mixed-up equipment components among thousands of such components,” Santos explains.

Considerations for cleaning biopharmaceutical process equipment

In biopharmaceutical manufacturing, process intensification can change the way the equipment is used and thus affects cleaning methods. Beth Kroeger and Paul Lopolito, senior managers for Technical Services at STERIS, shared some points to consider in an interview with Pharmaceutical Technology. Click to read: “Considerations for Cleaning Biopharmaceutical Process Equipment”.

PAT considerations

Process analytical technology (PAT) sensors in the equipment are a crucial part of continuous manufacturing systems, but, in some cases, such as near infrared (NIR) probes, they may be fragile and require special handling during assembly and disassembly, notes Santos. He adds that it is important to use the PAT vendor’s procedures for proper cleaning and maintenance. “Having additional instruments to address concurrently with cleaning of the manufacturing equipment is logistically quite demanding, requiring close communication and planning in order to keep operations running efficiently. Developing and controlling standard procedures with the right level of details and mistake-proofing become even more critical in the context of preventing damage to such sensitive components during handling and cleaning.”

“When cleaning equipment with internal sensors, consideration should be given to the material of construction to ensure compatibility with the chosen cleaning agent. Typical substrates may include glass, titanium, or polymeric material,” note Lopolito and Kroeger. If using a CIP cleaning method, they recommend working with the PAT vendor to check compatibility to determine if there will be any impact to the sensors through chemical exposure, high-pressure steam, foaming, build-up of residue on the probes, or through any interaction of materials.

Another concern with sensors in a CIP process is determining how well the cleaning and rinse solution flows in and around the sensor and whether there is a significant change in the flow dynamics through the piping. “Coverage testing can be confirmed using riboflavin, and flow dynamics can be assessed through computer modelling, Reynold’s number calculations, or inspection with a borescope,” they explain.

It may be possible to use the existing PAT (which measures process variables when the process is running) to also monitor a CIP cleaning process, says Lopolito. “An example would be an ultraviolet (UV) or Fourier Transform Infrared (FTIR) spectroscopy sensor (to monitor drug active) that can also be used to detect trace levels of cleaning agent in rinse water and stop the rinse process when a target limit is achieved within a specified time,” he explains.

FTIR is also being investigated as an approach to cleaning verification, using a handheld instrument to detect and quantify surface contamination (3).

One of the challenges for manual cleaning is the difficulty of standardizing across a wide range of equipment components with different degrees of product exposure or adhesion, notes Santos. “New technologies such as handheld FTIR can certainly bring a level of simplicity to this process, either in terms of an in-process control to determine the endpoint of cleaning of a component or to eliminate dependence on analytical samples altogether,” he concurs.