Use of the terms “Fake and/or False” in our vocabulary has become very pervasive since 2016. I thought it would be useful and helpful if we re-visit definitions of batch and continuous production processes and try to see if either of them fit in the context of these terms. My observations are based on my education, experiences in chemistry and chemical engineering and the prevailing practices established more than 100 years ago. They are also based on actual process design and development, scale up of developed processes and management of manufacturing processes and operations in fine/specialty chemicals, coatings and resins that were produced using organic chemicals.

In recent months, certain pharmaceutical processes have been labeled as continuous process but no process information has been shared. However, based on public information about the products their viability of being operated as a continuous process is extremely doubtful. Additional details are shared later.

Established batch and continuous process definitions and examples are reviewed after a brief overview of what chemical engineers are taught.

Fundamentals taught in chemical engineering
Chemical engineers are taught that every process should be safe, sustainable, and economic and should produce quality product the first time and all the time thereafter. If a product has to be reworked or its stoichiometry has to be adjusted during the process to produce a quality product, its cost goes up and profitability is lowered.

It is well known and practiced in every manufacturing industry that the market size demand influences the type of process used. Irrespective of the process used product quality is a must for the market success of every product. These expectations are most stringent for pharmaceuticals because they influence human life.

Chemical reactive processes are called unit processes¹ that produce a product that could be the final saleable product or could be an intermediate for another reactive or formulated product. Unit operations² involve a physical change or chemical transformation that are used in the chemical and allied industry to facilitate unit processes to produce the desired products. A combination of these makes a process and depending on demand it could be a batch or continuous process.

McGraw-Hill has published series3 of books that cover unit processes, unit operations and the economic considerations that allow chemical engineers and chemists to develop, design and commercialize processes that are economic and profitable to any individual or company. Excellent books have also been written about process control methods and strategies.⁴

Batch production
Wikipedia’s⁵ definition for batch production: Batch production is a technique used in manufacturing, in which the object in question is created stage by stage over a series of workstations (steps), and different batches of product/s are made. Batch production is most common in bakeries and in the manufacture of sports shoes, specialty/fine chemicals, resins, pharmaceutical ingredients (APIs), purifying water, inks, paints and adhesives. There are other formulated products and most prominent are finished pharmaceutical drug dosages.

Batch production processes generally require much lower investment and have an advantage because several products can be produced in the same equipment. However, if the same equipment is to be used for different products, productivity will be significantly lower⁶ compared to a process where the equipment is dedicated to produce a single product. If different products are to be produced in the same equipment, cleanliness becomes critical, especially for the APIs and their formulations. Idle (down) time can be high. Down time in the pharma industry is extremely high.⁷

For the pharmaceutical industry batch processes are the main stay in the manufacture of active ingredients (API) and their formulations. This is due to two inherent reasons. Micrograms to milligrams of API are needed in every dose. One kilogram of an active produces one million tablets of one milligram each. Thus, not a large quantity of the API is needed to satisfy the need. Table 1 is an illustration of the needed API and potential production methods for different dosages and number of patients.

Process economics, chemistry and execution method will determine type of process used. Typical available hours for production at any plant are about 8,400 (24x7x50) hours per year. How many of these available hours are used for the production of a single product define the production process. If less than 8,400 hours are used to produce a product such process according to the established norms⁵ will be a batch process. This holds true for API production and their formulations.

Table 2 is an illustration of how many hours per year are needed to produce at 200,000 tablets per hour at different doses. Production equipment of higher tableting rates are commercial and available. It’s likely most of the products would be formulated using batch processes even when they could be operated continuously.

Continuous production
The definition of continuous⁹ production has been long established. Continuous usually means operating 24 hours per day, seven days per week with infrequent maintenance shutdowns, such as semi-annual or annual. Time could be allocated for unexpected shutdowns. Excellent examples of continuous process are Earth’s rotation and our heartbeat. Can we imagine “stop and go” movement of earth and human heart?

On the pharma landscape, most likely there are ten or less APIs that are being produced by continuous processes. There are additional APIs that could be produced continuously10 but effort is needed to develop and commercialize such processes. An alternate business model and consolidation can convert batch processes to continuous processes, but there is a downside to the continuous processes. It will result in consolidation of operations especially among the contract API producers and formulators.

McNeil, a Johnson and Johnson subsidiary, could have built a continuous process due to the formulation volume of Tylenol but they did not and it was a missed opportunity.

Fake/false continuous processes
Somehow across the pharma landscape, processes that are in reality batch processes are being called continuous by chemical engineers working in both the public and private sectors. We all need to understand and recognize that if multiple products can be processed during the same calendar year using the same equipment by re-arranging the reactive chemistry or the formulations, their processes should not be called “continuous manufacturing.” Any process that has a wide spot in the manufacturing line—material is held for any time period—the process is a batch process.

FDA¹¹ does not have an established definition and I am told one is forthcoming. I wonder how different it would be from the currently established and practiced methods.

API example
Analyzing Table 1, we have an example of a drug that has 100,000 patients. They have to take 200 mg dose every day of the year. Total API needed is about 7,300 Kg. per year. This product would and should be produced using a batch process with the available equipment. If each batch reaction produced about 250 kilos per batch, about 30 batches per year would be needed. If each batch took 30 hours per batch all of the API would be produced in about eight weeks. If they campaigned the whole production for the first two months of every year, this would not make their process a continuous process. If this campaign run was called a “continuous process” then it would be an incorrect characterization and I would label this process a “fake/false continuous process.”

Formulation example
If the example of the API above was to be formulated and tableted, the product can be produced at single plant in less than 200 hours at 200,000 tablets per hour. However, if the tableting were done at 10,000 tablets per hour, it would take them six months to produce the total demand. It still does not make the process continuous, as the equipment would be sitting idle for six months every year. It would be a wasted investment earning no return. Again, if the process was called a continuous process, it would be an incorrect characterization and I would label this process a “fake/false continuous process.”

Vertex⁸ has claimed to have a continuous process for their cystic fibrosis (CF) drug. With less than 80,000 patients worldwide, they do not have a large enough global patient (~80,000) base for all of their CF drugs and cannot operate their equipment for 8,400 hours per year per drug.

To me, an incorrect characterization of established definitions seems to have become a new trend especially across the pharma landscape. Is it because the U.S. FDA is mentioning continuous manufacturing in their communications and the industry wants to look good by calling a naturally batch process a continuous process? Thus, if we accept an incorrect definition then we should be also ready to accept 2+2=6.

QA in batch and continuous processes
Meeting quality standards in batch as well as continuous processes have different rigors. Command of the processes is a must whether it is a batch or a continuous process. If command and understanding of the processing steps are lacking, invariably there could be a batch-to-batch and/or a lot-to-lot quality variation. Efforts to rework or bring the material to quality can and often results in waste, i.e. higher product costs.

In batch processes due to their stop and go nature quality can be sometimes managed and the process adjusted to achieve the established quality benchmarks. Thus an absolute command of the batch process is less stressful but still is necessary. Batch processes are based on in-process quality checks and adjustments. This practice extends cycle time and adds to inventory—raw material, in-process, work in process and finished goods—challenges. If the batch process cannot be adjusted to correct process deviation, significant waste can result. In the simplest terms, batch processes have economic value for products that do not require continuous production but their quality testing can be an aggravation.

Compared to batch processes, continuous processes have much higher process control demand. Since the process is running with minimal/no stop time, it is extremely critical that process operating parameters do not deviate outside the established process operating control limits. If the process deviates outside the established control limits, significant quantities of waste and financial loss can result. Continuous processes demand that the quality be established through robust process design when the process is developed, designed and commercialized.

The debate on what is a continuous or a fake/false continuous process will go on until the economic realities of investment that have been well established are understood. One thing is sure, unless one has not justified, developed, designed or commercialized a process, it is difficult to discern the value of the developed process. No investment would be made for namesake unless it can be justified and meets the established norms of the science, economics and engineering.

As I said earlier, a batch process cannot be continuous and vise versa. If we accept it otherwise then we have a case of “false/fake” science, engineering, economics and human intelligence.