Cynthia A. Challener is a contributing editor to Pharmaceutical Technology.

Cynthia A. Challener

Rapid changeover of biologic production processes carries numerous challenges. Challenges to rapid changeover come from many sources, including the equipment, room configuration, documentation, people, and environmental monitoring, according to Sebastien Ribault, head of end-to-end solutions at MilliporeSigma.

The traditional method of completely stripping down all equipment and installing dedicated materials and components for each product has proven to be a cumbersome and costly process for multiproduct facilities, adds Piergiuseppe Nestola, senior platform technology consultant at Sartorius. “It is not unusual for changeover to require weeks to complete when traditional methods are followed. With the changing industry tide favoring multiproduct manufacturing facilities, methods to enhance efficiency without sacrificing quality or safety are needed,” he says.

Several activities must be performed in a facility to avoid any risk of cross-contamination between Product A and Product B, in particular via a thorough cleaning-in-place of all equipment surfaces in contact with intermediates and the end product, Thibaud Stoll, global head of commercial biologics operations at Lonza, specifies.

For certain biologics, most notably viral vectors, vaccines based on live viruses, and spore-formers, precautions must be taken to prevent spread through the air and more extensive cleaning protocols are generally required, typically with airborne peroxide methodology, says Katarina Stenklo, enterprise solutions commercial activation leader with Cytiva. Any live biological agents, whether they be the host organisms or adventitious agents, must be effectively removed/inactivated from HVAC, facility, and equipment surfaces (both exterior and product paths) prior to introduction of a subsequent product, adds Syed T. Husain, senior vice president and CDMO business unit head at Emergent BioSolutions.

Stainless-steel equipment specifically presents a common challenge, as it requires cleaning and validation of product contact surfaces before the equipment can be used for a subsequent project, according to Evan Shave, director of biomanufacturing—global network operations for Thermo Fisher Scientific. Cleaning and sterilization of stainless-steel equipment is well understood, but often “overdone” in terms of cleaning and rinse times, mostly due to conservatism or a lack of time to properly optimize the process, adds John Machulski, vice president of engineering for Catalent Biologics.

Changeover of processes performed in a ballroom setting can be even more difficult than for processes run in individual suites due to the added risk of cross-contamination with other processes on top of concerns regarding product carryover, notes Steve Gravallese, enterprise solutions program director at Cytiva.

Stoll adds that some product-dedicated equipment must also be installed, in particular chromatography columns with packed resin for drug substance purification. “All these activities may potentially be quite long and on the critical path if not optimized and sequenced properly, and if the facility layout has not been designed accordingly,” Stoll states.

For drug product manufacturing, it is critical to have a lean process design due to its highly kinetic nature, according to Machulski. “Although barrier isolation technology provides the highest level of aseptic processing, long bio-decontamination cycle times remain one of the biggest challenges for achieving a rapid changeover,” he says. Stoll also notes that given the completely different types of equipment, changeover times are difficult to compare. “A change in vial format may require some significant setup activities for a filling line; the number of such changes can be optimized via the proper yearly planning and sequencing of campaigns,” he observes.

Strategies for optimization of process changeovers differ because the equipment and room configurations for each process are different, but all are driven by the same constraints and rational, according to Ribault. “A combination of primary (process design), secondary (facility design and operation), and procedural controls and studies should be used,” states Husain.

Stoll identifies three key approaches to optimizing changeover activities: making them as short as possible, performing them during “hidden time” or in parallel, and reducing the number of changeovers by running longer campaigns. “Operational excellence/lean methodologies can be quite powerful for optimizing changeover processes, as can the use of redundant equipment or dedicating packing rooms for chromatography columns. In the latter case, there is additional capital expense, but it is usually a good investment,” he says. Running longer campaigns, though, carries a trade-off with the optimization of product inventory.

The ultimate goal, according to Gravallese, is optimizing the facility around unit operations so they can be segregated where open processing cannot be avoided and staggered changeovers are possible. “It really comes down to identifying the best methodologies and designs to stagger processes in facilities without impacting operations in the balance of the site,” he states.

Properly optimizing cleaning and sterilization cycles where stainless-steel equipment is used, validating procedures, having a well-trained staff, and having a robust yet simplified supply chain are keys to facilitating rapid changeovers, according to Machulski. “Additionally, ready-to-use primary and secondary components can be helpful, along with automation and robotic technology for drug product fill/finish manufacturing,” he says.

Ribault also asserts that it is important to look across the entire value chain and consider how to ensure the interface between process development and manufacturing works well; another consideration is to put together a team that will make the project a success in record time. “You do these things by having templates in place for process development and manufacturing that reduce the transition time. So, while rapid changeover is certainly an integral aspect of operations, it is important to keep in mind that it is one piece within the entire value chain,” he says.

In addition, a quality risk management approach may be applied to assess and continuously improve established changeover processes, according to Nestola. “All processes, including changeovers, can be improved with investment of money and resources, parallel activities, equipment design improvements, and standardization,” he asserts.

Cynthia Challener is a contributing editor to 

Articles

Equipment and facility cleaning is crucial, with more extensive protocols needed for some biologics.

Considering Changeovers in Multiproduct Biologics Manufacturing Facilities

With additional safety protocols required in the manufacturing environment, gatherings of large people generally prohibited, and onsite inspections limited due to restricted travel, ensuring quality throughout the supply chain from raw material to API is more challenging. API producers have responded rapidly, implementing safety protocols, leveraging digital tools and technologies for virtual audits and inspections, and generally taking a reasoned, risk-based approach for making use of available resources.

FDA has conducted mission-critical inspections, assessed records remotely using the authority under Section 704(a)(4) of the Food Drug & Cosmetic Act, and has developed a risk assessment system to help the agency use dynamic information to qualitatively assess COVID-19 cases in a local area based on state and national data and make informed risk-based decisions on when and where to resume prioritized domestic surveillance inspections.

Importance of using a risk-based approach

In a time of crisis, risk-based decision making and strong leadership take on new meaning, according to David Waddington, NSF International’s executive director of pharmaceutical services for Europe, Middle East, and Africa. “It’s simply not possible for companies to operate their pharmaceutical quality systems (PQSs) and meet all their commitments with such a drastic reduction in available resources. Forward-thinking organizations have taken a proactive approach to deciding what activities can be stopped or delayed. Stopping an activity may seem to be extreme, but taking this decision proactively, before the quality system slips out of control, is a sensible approach,” he says.

For example, Waddington notes that change controls that have not yet been implemented could be halted without reducing validation effort, regulatory affairs work, quality control (QC) testing, and documentation updates. “Being extremely stringent with limiting change controls can free up [quality assurance] QA and QC resources,” he adds. Similarly, improvement plans such as introducing new systems could be halted, again freeing up resources. While delaying compliance activities feels wrong, Waddington says that in extreme situations it can be done using the quality system.

Activities that should be continued are those linked to batch release and testing. “It is important to ensure that there are sufficient QA/QC staff to support production activity and, if necessary, to reduce planned output. Deviations and out-of-specification/trend activities should also be performed in a timely manner to ensure product flow and also to identify any problems as early as possible,” observes Waddington. If action has been taken to stop some activities at the site and delay others, then, he comments, some staff may be re-deployed to bolster frontline staff.

“Taking a hard look at all activities that consume resources and applying a risk-assessment approach can help to free up some resources to bolster direct product fulfillment activities and thereby keep critical medicinal products flowing to patients,” Waddington concludes.

Because of the nature of pharmaceutical manufacturing and the need to ensure both operator safety and product quality, extensive systems and procedures are already in place at facilities producing pharmaceutical intermediates and APIs, including regular use of personal protective equipment (PPE) and good hygiene practices. Manufacturers, as a result, have been able to adapt quickly to new safety requirements and ensure continued supply of critical medicines according to current good manufacturing practices (CGMPs) and other regulatory requirements. This compliance is happening despite the challenges created by temporary plant shutdowns, the need for social distancing, and reduced on-site staff at a time of increasing production demands, complex supply chain challenges, and existing product shortages, according to Waddington. “It’s not uncommon for facilities to be operating with at least 30% less staff and key support functions, including QA, working remotely. Both companies and regulators are having to make some tough choices,” he says.

Fortunately, because API manufacturing is different from many other types of manufacturing, the need to exercise social distancing in these situations does not affect the nature of most processes, according to Jeff Ross, director of environmental health and safety for Cambrex Charles City.

“Outside of the need for social distancing, Cambrex was an early adopter in implementing screening protocols for anyone entering the site. Today, employees are required to undertake a daily temperature check in addition to answering a series of health questions. Any visitors to the site must also go through the same process and need to complete a formal questionnaire,” Ross says. Cambrex also performs job hazard analyses for all operational areas and makes recommendations on a variety of different elements in the typical workday, such as room capacities, the necessary frequency of sanitization, and the maximum size of any essential gathering.

Employee safety is always a priority for Thermo Fisher Scientific, and since the start of the COVID-19 pandemic the company has focused on protecting their health and safety while continuing to serve the needs of its customers, according to Vice President of Drug Substance Quality,Ben Gerlach. “Manufacturing safe APIs for medicines that can improve or save the lives of patients is both a large responsibility and a privilege. During the COVID-19 pandemic, we have continued to ensure the safety, efficacy, quality, and availability of the APIs we manufacture through a globally coordinated response, comprehensive site preparedness, employee training and communication, and robust business continuity planning,” he comments.

Thermo Fisher Scientific manufacturing sites have specifically established increased hygiene protocols and tightened visitor guidelines. Stringent preventative measures developed in line with guidance from the World Health Organization, US Centers for Disease Control and Prevention, and local government agencies include restricting employee travel, encouraging remote work, enforcing social distancing, and requiring employees to wear masks at all times, according to Gerlach. For those employees who are on-site, the company keeps contact logbooks, takes employees’ temperatures regularly, and employs a two-shift system for teams in the laboratories and on the manufacturing floor to accommodate social distancing.

“As a result of the support, flexibility, and discipline of our colleagues and supply chain partners, as well as the IT infrastructure available, all Thermo Fisher API manufacturing sites have remained operational since the start of the pandemic with continued GMP compliance,” Gerlach remarks.

Maintaining close communication with suppliers

Key to ongoing provision of API to pharma customers is effective management of the supply chain, including assurance that materials continue to meet the high-quality standards of the pharma industry. Prior to the COVID-19 pandemic, many API manufacturers made use of international industry conferences to meet with their vendors and customers, from raw material producers to contract research organizations, and contract development and manufacturing partners. Travel restrictions and the prohibition of large gatherings, both designed to limit spread of the SARS-CoV-2 virus, have forced API producers to find other means of keeping track of the supply chain.

FDA Takes Calculated Approach to Auditing During COVID-19

Despite being unable to attend major industry conferences in-person, representatives of Thermo Fisher Scientific have joined events virtually and maintained close communication with supply-chain partners to ensure there is no change in quality or availability of raw material, according to Gerlach. In addition, the company’s regional teams continue to closely monitor the COVID-19 situation, particularly in Asia, Europe, and North America, where most of its qualified suppliers are located. “We also continue to closely track our purchase orders and have put a major focus on regional governmental restrictions that could affect manufacturing and shipping and the timely availability of raw materials and critical equipment so there is no lapse in our ability to help customers bring important medicines to market as fast as possible,” Gerlach says.

Before the pandemic ever emerged, Cambrex had prepared for various emergencies and crisis situations by undertaking strategic logistics planning and implementing response processes, according to Ross. “Over the past several months, we have been working strategically to expand the supply chain globally by evaluating suppliers across the globe, including those in the [European Union] EU or US. Expanding our footprint and ensuring supply chain redundancy has enabled us to minimize the risk of supply chain interruptions and work with partners efficiently,” he explains.

Because of the circumstances connected with COVID-19, Ross also stresses that it is extremely important to frequently engage with supply chain partners to ensure that Cambrex understands the impact of the pandemic on their businesses and any potential downstream effects on Cambrex’s unit operations that might ensue. “Video conferencing and more frequent communications have been important for our continued visibility into the supply chain,” he asserts.

Effective communication, which Waddington says involves listening more and speaking only when there is something valuable to say, has enabled NSF International to successfully transition from a training, consultancy, and auditing service provider that operated primarily face-to-face with clients to one that can now provide true virtual and blended learning, remote audits, and consultancy. “We believe we have achieved a truly remarkable transition in such a short time frame, as have many of our pharma industry clients,” he states.

Leveraging digital tools and technologies

That rapid transition has been made possible by leveraging a wide range of digital tools and technologies in new ways and to a much greater extent than API manufacturers and their suppliers and customers were previously accustomed to. The most obvious change, according to Waddington, is the reliance on digital meeting platforms. “We have seen a significant increase in the need and willingness for more regular video calls and sharing of documents and information through secure file handling platforms. Participants can often feel self-conscious to begin with, but soon adapt and get to grips with presenting, using whiteboards, interacting breakout rooms etc.,” he observes.

As part its digital transformation strategy, Thermo Fisher had already implemented digital tools to support many of its GMP processes, and many of these systems have proven to be highly beneficial to ensuring continued API quality, according to Gerlach. As an example, he points to the company’s SampleManager Laboratory Information Management System, which helps drive productivity, ensure compliance, streamline processes, and improve organizational efficiency.

Thermo Fisher also uses Documentum (OpenText) to store GxP documentation and manage the creation, amendment, approval, use, and retention of all documents. “This system provides traceability, ensuring data integrity and compliance to good documentation practices to meet our regulatory standards,” Gerlach notes. The company also uses tools to manage quality events and support training and virtual communication and systems for electronic process control and data analysis. Cutting-edge camera and augmented reality (AR)/mixed reality technology is also leveraged to provide safe, virtual access to Thermo Fisher facilities.

Cambrex has also invested heavily in recent years in information technology platforms and advanced technologies that have enabled the company to maintain its current quality systems while allowing remote working for staff and facilitation of virtual collaboration with internal and external stakeholders, according to Chuck Walker, director of regulatory compliance at Cambrex’s Charles City facility.

Examples include live broadcasting from Cambrex’s manufacturing sites and clients being able to remotely visit its facilities, have instant interaction with subject matter experts, and undertake live-virtual audits. “When lockdown conditions were implemented at our multiple sites, we saw immediate results from these investments in that our employees were able to operate as usual from remote locations; client visits became virtual; and we were still able to undertake internal and external audits,” Walker observes.

In fact, from an auditing perspective, NSF International has witnessed a major shift with companies allowing the use of camera technology within facilities to share images, according to Waddington. “This approach is a real game-changer as it transitions from a virtual ‘desktop’ audit to a true interactive remote audit, allowing the auditor to view operations live and assess effective implementation of the PQS including remotely observing facility design, hygiene, and even operator behaviors,” he explains.

Such digital tools have also been invaluable for regulatory agencies during a period when most onsite inspections have been halted due to the COVID-19 pandemic. Many agencies have historically conducted some form of remote risk-based review or “desktop” assessment, so in some respects their current approach is an extension of that process, according to Waddington. One additional challenge that regulatory authorities have had to face, though, is to ensure the processes they are following have legal standing in line with legislation in place in their respective countries. “A number of agencies, including the [United Kingdom’s Medicines and Healthcare products Agency] UK MHRA, have been successfully conducting very detailed remote inspections of facilities and have been able to follow up on for-cause audits and ensure remediation programs are progressing in line with company commitments,” he says.

The use of AR technology, Gerlach adds, enables Thermo Fisher to provide regulatory agencies unprecedented access to its facilities without them needing to be physically present. “Auditors can navigate through the facilities and perform factory acceptance tests. Remote assist provides the means to facilitate support both internally and externally from anywhere in the world,” he says. “Limiting onsite visits helps protect both employees and visitors without impeding operations or impacting quality,” Gerlach continues. “All of these solutions are made possible with training from the augmented execution team and tremendous collaboration from our sites, vendors, clients and regulatory agencies,” he concludes.

Cambrex deployed virtual live tour technologies throughout its facilities when lockdown and restricted access conditions became applicable. “These technologies have enabled both client audits and regulatory audits to continue,” Walker says. “Although we have not had any direct regulatory requests during this period at our Charles City [Iowa] facilities, many of our other sites in different locations have successfully undertaken virtual audits, and we are fully prepared for live virtual audits if needed here at Charles City,” he notes.

In fact, Walker believes that the API industry in the United States is innately equipped to manage the COVID-19 pandemic given the governing force behind employee protections with US Occupational Safety and Health Administration’s industrial standards. “Because safety is already so deeply engrained in our daily operations, along with engineering controls, we have been able to operate confidently knowing we are protecting our employees and product simultaneously,” he asserts.

API manufacturers have also invested in expanding capacity for specialized intermediates and APIs in recent years, which has also contributed to the ability of contract service providers to meet growing demand during the pandemic. Thermo Fisher, for instance, invested more than $800 million to increase capacity and meet rising demand for biologics, cell and gene therapies, and drug products. “These global and strategic investments have ensured that lack of capabilities, capacity, or supply is never a reason medicines are delayed in reaching patients,” Gerlach asserts. “We continue to protect our colleagues on the manufacturing floor and in our testing laboratories and warehouses by adhering to strict safety measures and requirements. At the same time, we remain flexible, creative, and vigilant to ensure API quality and supply as we continue to work to bring medicines to market as fast as possible for customers and the patients they serve,” he concludes.

As horrible as the COVID-19 pandemic has been and continues to be, it, like all crises, has presented opportunities for improvement as well. “If there is a silver lining to the current situation, it will lie with those employees who stepped forward for their colleagues and found creative ways to get things done. Or it may lie in the cross-training of employees for new or expanded roles,” Waddington states. For instance, he points out that key decisions around product quality may be delegated closer to the unit operation, which should result in efficiency gains.

Cynthia A. Challener, PhD, is a contributing editor to 

Pharmaceutical Technology
Vol. 44, No. 9
September 2020
Pages: 22­-27

When referring to this article, please cite it as C. Challener, “Tracking API Quality During a Pandemic,” 

Risk-based decision-making is impacting all aspects of manufacturing quality from raw material supply to facility inspections. 

Tracking API Quality During a Pandemic

Although inspections are critical, according to US Food and Drug Administration Commissioner Stephen M. Hahn, they are one part of a robust and multi-pronged approach to overseeing the safety and quality of FDA-regulated products. “Safety and quality must be part of the daily routine at a firm for their products to be high quality and reliably suitable for the US consumer,” he explained in previous press statements from the FDA press office.

Under normal circumstances, the agency uses risk-based models to identify firms for inspection. FDA prioritizes for inspection facilities deemed as higher-risk based on specific, defined criteria. For drug and device inspections, these criteria can include inherent product risk. To supplement inspections, FDA also uses a number of other tools, including denying entry of unsafe products into the United States; physical examinations and/or product sampling at US borders; reviewing a firm’s previous compliance history; using information sharing from foreign governments as part of mutual recognition and confidentiality agreements; and requesting records “in advance of or in lieu of” on-site drug inspections.

Furthermore, FDA will conduct inspections when a potential risk to public health is detected, and the agency has remained in contact with domestic and foreign regulatory counterparts to identify emerging risks in the medical products and food supply systems, according to an FDA spokesperson. “When we suspended routine operations, mission critical inspections were conducted for products deemed as mission critical drugs because of reasons including medical necessity, drugs for which there is a shortage, and pre-approval inspections for novel drugs or drugs related to the potential treatment of COVID-19,” says the spokesperson.

Both for-cause and pre-approval inspections can be deemed mission critical. They are identified on a case-by-case basis by the agency and conducted with appropriate safety measures in place.

Where routine domestic and foreign surveillance inspections have been postponed during the COVID-19 pandemic, FDA has used and implemented additional alternative approaches and records reviews, including, among other things, when appropriate evaluating records in lieu of conducting certain onsite inspections on an interim basis when travel is not permissible, according to an FDA spokesperson. The agency’s labs also continue to analyze high-priority samples.

“The resumption of prioritized domestic surveillance inspections has been an important area of focus for us,” the FDA spokesperson observes. As of July 10, 2020, FDA was working toward the goal of restarting routine on-site domestic inspections during the week of July 20. Resuming prioritized domestic inspections is, however, dependent on the data about the virus’ trajectory in a given state and locality and the rules and guidelines that are put in place by state and local governments, according to whom. “In order to move to the next phase, we must see downward trends in new cases of COVID-19 and hospitalizations in a given area,” noted Hahn in an FDA statement.

Preparation for restarting on-site prioritized domestic inspections involves using the tools available while considering other factors including the operational status of the facility, the ability for the appropriate investigator to travel, evolving local, state, and federal requirements, and updates to Centers for Disease Control (CDC) guidance. “We are using a newly developed risk assessment system to help it, and individual states make informed risk-based decisions on when and where to resume prioritized domestic surveillance inspections,” says the FDA spokesperson.

In addition, for the foreseeable future, prioritized domestic inspections will be pre-announced to FDA-regulated businesses to help assure the safety of the investigator and the firm’s employees. This approach will provide for the “safest possible environment to accomplish our regulatory activities while also ensuring the appropriate staff are on-site to assist FDA staff with inspection activities,” Hahn says.

FDA relies on risk assessments, border inspections, and compliance histories in place of routine audits during the COVID-19 pandemic.

FDA Takes Calculated Approach to Auditing during COVID-19

Continuous manufacturing is being encouraged by regulatory authorities as a means for improving product consistency and quality while also potentially reducing cost. For continuous manufacturing of oral solid dosage drugs, excipients play important roles not only in the performance of the formulated product, but also during processing. Excipients must address the specific needs of the API, such as the desired drug release rate, solubility enhancement, crystallization inhibition, or improved API uniformity while also enabling processing of the final intended dosage form. In the latter case, physiochemical properties such as flowability, density, particle morphology, and glass-transition temperature are crucial considerations for designing an optimal continuous process.

For each given excipient, the impact on a continuous process may be small or substantial depending on the quantity of excipient present and its difference in properties from that of the API. Many excipients available today are well suited for continuous processing, but there remain significant opportunities for increasing knowledge about the impact of material property changes in process output and, ultimately, drug product quality.

“The excipient impact on continuous drug product manufacture is profound,” asserts Joseph Zeleznik, technical product manager for IMCD US Pharmaceuticals. “The proper choice and use level influence product and process robustness, throughput and yield, development and manufacturing costs, and drug product quality. It is important that any excipient used is not only effective in its application within the formulation but is well-suited to maximize continuous manufacturing process efficiency,” he adds.

For oral solid dosage (OSD) drugs, excipients can have an impact on the physical characteristics (i.e., flow, density, homogeneity, and compactability) of the mixture in the equipment during processing and ultimately at compression or encapsulation, notes Anthony Carpanzano, director of R&D at JRS Pharma in the United States. Blend homogeneity is critical for achieving content uniformity in the finished tablet, according to Mark Dreibelbis, associate research scientist with DuPont Nutrition & Biosciences. “Large mismatches in particle size and flowability between excipients and the API can lead to segregation, impacting dosage consistency and possibly leading to excursions from the therapeutic window,” he explains. Inter- and intra-lot excipient variability should be understood, as well as its potential impact on process and product quality Zeleznik observes.

“Excipients can be a double-edged sword for OSD continuous manufacturing processes,” states Krizia Karry, global technical marketing manager at BASF Pharma Solutions. “They can be used to improve flowability and tabletability, but they may also affect dissolution performance if they are shear dependent, for example. My recommendation is to steer away from excipients that are very shear dependent as these can lead to inconsistent residence time distributions, and those with broad particle size ranges and/or high specific surface area, as fines are more prone to gaining static charge and bridging,” she says.

A quality-by-design (QbD) development program supported by an appropriate process analytical technology (PAT) strategy is essential in understanding and controlling excipient impact on continuous manufacture and drug product quality and performance, according to Zeleznik. Lubrication strategies also need to be rethought not only with respect to the right choice of lubricant, but the right use level and when it should be added.

In batch manufacturing, Krizia explains, there is not too much emphasis placed on flow characteristics, shear, or electrostatics because the batch dispensing process is manual (you open a bag and dispense into an [intermediate bulk container] IBC, or you use a vacuum system) and subsequent unit operations are discrete. “In continuous processing, the impact of compactability (change in volume with force) when refilling materials, flowability (how easy the material moves through the line), and shear (which also dictates your feeder screw set-up because you want to feed accurately and without breaking the material) must be considered, among other factors,” she says.

Overall, Zeleznik comments that continuous manufacture is no different than batch manufacture regarding choosing the “right” excipient. “Excipient choice is predicated on several factors, including API physicochemical characteristics, targeted dose, route of administration, and most importantly, the manufacturing equipment and process used during continuous manufacture,” he says. “Another consideration in choosing an excipient is its multifunctionality and flexibility with respect to the formulation and process. Excipients to avoid are those having limited performance attributes or that are unsuitable for continuous operations. Because of the limited feeders, more has to be accomplished with less.”

It is important, therefore, to develop a formulation with the desired functionality. The flow, density, particle size, and electrostatic properties of excipients are more important in continuous processes versus traditional batch processes, according to Mara van Haandel, innovation manager at DFE Pharma. “During continuous manufacture, it is essential that product flows in a continuous manner in the processing units (and is consistently transported from one unit to the next), as clogging of material/material build up can impact the residence time distribution,” she says. Hence, the “right” excipient choices have to be made from the start of developing a formulation on a continuous process.

That can be a challenge for OSD formulations because powders of various particle sizes and densities must be meter-fed into the system at the correct ratios and then make their way through the production path, notes Becca Putans, an associate chemist from DuPont. “Materials that have a poor flowability or high cohesive properties pose a risk of accumulating in corners, causing blockages, downtime for cleaning, and non-uniform dosage forms,” she says.

Any excipient chosen also needs to demonstrate a non-segregation potential for the final blend. “Since the materials move continuously together through the unit operations, the mixture must stay at the correct ratio, otherwise the resulting dosage forms will not have a uniform distribution of the active ingredient,” Putans adds. Therefore, excipients with higher flowability, optimized density, morphology, and moisture content, low batch-to-batch variability, and compactability are preferred.

The physical behavior of an excipient when under shear stress is a major determining factor in its suitability for continuous processing, adds Carpanzano. “Excipients that perform well in continuous manufacturing can be easily fed into the process at a uniform rate, promote blending with the active ingredient and other excipients, maintain flow and do not break down or compact in the mixing phase, and can be compacted into tablets or filled into capsules after blending,” he concludes.

Many direct compression excipients have been designed for use in a continuous tableting operation, according to Putans. The particle size and morphology have been tailored to provide a high level of flowability while retaining compactability. “These materials are designed to flow through a continuous manufacturing process with little build-up, while maintaining content uniformity and good final dosage consistency,” she observes.

In some cases, a pre-blending strategy is adopted to improve flowability, such as with fumed silica when used as a glidant, according to Karry. “Fumed silica has a low density of 0.03 g/mL, which presents challenges when trying to individually dispense via loss-in-weight feeders. “To overcome this issue, formulators pre-blend the glidant with another excipient to ensure accurate feeding and good flow properties of the blend. Undoubtedly, pre-blending with silica is not ideal—especially in a continuous manufacturing setting—but it is a proven strategy for improving powder flowability,” she says.

“Improving flow properties with excipients is a proven strategy, but for troublesome low-density and/or poor water-soluble APIs, additional unit operations have also been adopted to continuous platforms,” adds Karry. Twin-screw granulation or hot-melt extrusion excipients intended for preprocessing of these APIs should have wide operating temperature ranges and resist degradation, discoloration, or drastic changes in viscosity, according to Dreibelbis.

Binder selection is also critical for continuous granulation processes for uptake of granulation liquid and quick drying to produce robust granules. Less hydrophilic grades of common binders exist to facilitate faster moisture removal from the resulting granules, which ultimately reduces cost and improves throughput, he adds.

Compared to batch processes, electrostatics (measured as static charge) is a critical piece of the puzzle for both APIs and excipients. “When a material bridge occurs due to electrostatics,” Karry explains, “material is likely not being fed through the conveying screw elements, and thus, there is no registry of weight change over time. This absent change triggers a control reaction (since feeders have Level 1 control) that involves increasing the screw speed to ‘try’ to dispense more material. Since the material is stuck on the hopper, no material is fed and the result is a subpotent (for the case of API) or superpotent (if the case is for filler) blend. The blend amount produced during this time will depend on the total mass flowrate of the process, the mean residence time, the alarm limits, and the controller dead-time.”

The problem, Karry adds, is that few options exist for accurately measuring this attribute and electrostatic properties depend on the humidity, temperature, and contact material. It is therefore important when evaluating performance to replicate the manufacturing conditions.

van Haandel notes it is unlikely that a powder will bridge due to electrostatic behavior in a hopper/feeder, but due to the combination of wall friction and hopper/feeder flow mostly caused by powder consolidation and/or incorrect powder flow in relationship to the opening diameter.

In a continuous process, ingredients need to be fed in at an appropriate rate and at the correct ratio. When there are many different ingredients, it can be challenging and costly to have feeders dedicated to each individual component. To reduce the number of feeders that must be aligned, co-processed excipients offer an effective solution, and also reduce the number of variables and opportunities for variability in a process, according to van Haandel.

“A single high-functionality co-processed excipient can accomplish the same task using only one feeder, thus enhancing finished product performance while keeping variability to a minimum,” Carpanzano agrees. A typical coprocessed excipient has a filler, a binder, and a disintegrant as part of its structure, as well as a low concentration of glidant to ensure excellent flow, according to Karry. “In addition to eliminating the need for multiple feeders, the use of such co-processed excipients simplifies the control architecture and control strategy for continuous processes,” she notes. There is also less chance of segregation of the components during mixing, according to Carpanzano.

In fact, Zeleznik asserts that multifunctional excipients are an essential part of a successful, robust formulation and process. “While not new, co-processed excipients offer the increased, multifunctional performance needed for continuous operations,” he says. DuPont, BASF, DFE Pharma, and JRS Pharma all offer advanced co-processed excipients with the flexibility and enhanced multifunctionality ideal for use in continuous production of OSD formulations. “Modifications to existing excipients, such as particle engineering, and advances in excipient performance through co-processing have accelerated the development of continuous processing, and specifically, continuous manufacture of directly compressed tablets,” Zeleznik concludes.

Consistent performance of excipients is essential for continuous manufacturing. So is a constant feed in and out of a continuous process to ensure traceability and control of all critical process parameters. “Because excipients have inherent variation, it is important to understand the implications of this variation on continuous processes and thereby final products,” states van Haandel.

Therefore, simplification of a formulation combined with the use of very consistent excipients is important. DFE Pharma is applying fundamental and mechanistic analyses to gain an understanding of the impact of potential excipient variation on continuous manufacturing processes and the performance of final products. Using this knowledge in formulation development is essential for successful implementation, according to van Haandel. “Formulations should be designed in such a way that they can cope with the variation proven in historical data and analyzed using multivariate statistics,” she states.

Specifically, DFE Pharma is applying multivariate analysis on all physical/chemical parameters to gain that needed better understanding of historical product variation and is offering stretch batches, or batches showing high multivariate variation to ensure they are representative of the historical product variation (five years of manufacturing-based data), to enable formulators to efficiently test the impact of this variation on their formulations.

DuPont is also analyzing critical excipient attributes, providing historical (four to five years) manufacturing data to establish inherent excipient variability, and performing comprehensive multivariate analysis on many grades to understand the variability within batches and at different manufacturing sites, according to Dreibelbis.

Karry adds that research centers and companies alike have developed excipient libraries that serve as input to mechanistic models that predict the impact of raw material property changes on feeding accuracy, hold-up mass, mean residence time, and downstream drug product concentration. These models are verified with tracer experiments that seek to measure the change in concentration as a function of time and total mass flowrate.

Unfortunately, according to Karry, the selection of these tracers is not a trivial task, because formulators need to consider the strengths of their spectroscopic signals (near-infrared or Raman, typically), and their bulk properties, as their addition into the blend should not affect the bulk flowing properties that one intends to study. “Such a perfect tracer does not currently exist,” she says.

Another important issue that needs to be addressed, according to Karry, is cleaning. “Taking apart, cleaning, and correctly reassembling every component of a continuous manufacturing line is basically a work of art,” she stresses. “Companies that have implemented continuous manufacturing processes agree that this task requires much more attention than with batch processes and that it has an impact on the supply chain because turnover times are greatly increased,” Karry says.

Modular equipment that can be easily cleaned in place has advantages, but piping, mixers, and contact parts still need to be disassembled for proper cleaning and reassembled prior to starting the next campaign. “An integrated line can have hundreds of parts, so the question we must ask ourselves is ‘Why disassemble?’,” Karry poses. With the right excipient, she envisions a ‘flushing’ type of cleaning process based on electrostatics. “The adequate balance of charges would pull everything in its path, and a non-contact hand-held spectroscopic device could be used for measuring the ‘cleanliness’ of the surface,” explains Karry.

Need for a novel excipient approval pathway

While formulation and process challenges for continuous manufacturing are being addressed through advances in excipient technologies such as particle engineering and co-processing, a regulatory gap continues with novel excipient acceptance, according to Zeleznik. “New or novel excipients are often avoided due to the perceived risk associated with using a new excipient even when a novel excipient’s performance could expedite drug product development and enhance continuous manufacturing processes,” he says.

There might be some changes coming, however. FDA is now considering a pilot program for novel excipient assessment (1). “Should this program be formalized and novel excipients have an acceptance pathway, it could do much to advance continuous manufacture growth going forward,” Zeleznik believes.

Novel Excipient Review Program Proposal; Request for Information and Comments


Vol. 44, No. 8
August 2020
Pages: 21­-24

When referring to this article, please cite it as C. Challener, “Key Ingredients Needed to Drive the Success of Continuous Manufacturing,” 

Understanding and overcoming excipient variation are crucial for successful continuous processes.

Author | Cynthia A. Challener