Determining Minimum Batch Size

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Pharmaceutical Technology, Pharmaceutical Technology-09-01-2016, Volume 2016 Supplement, Issue 3
Pages: s16–s19

Flexible batch sizes for semi-continuous unit operations, such as tableting and encapsulation, can improve efficiency while maintaining quality.

Establishing a commercial batch size is a crucial decision in pharmaceutical operations. It is influenced by the type of manufacturing technology being used, regulatory filing commitments, supply chain demand, and operational planning factors. To understand batch size, the differences between “batch,” “continuous,” “semi-batch,” and “semi-continuous” manufacturing must first be defined (1). In batch manufacturing, all materials are charged before the start of processing and discharged at the end of processing. Examples include bin blending and lyophilization. Continuous manufacturing involves materials simultaneously charged and discharged from the process; examples are found in petroleum refining, food processing, and, more recently, in pharmaceutical manufacturing. Other manufacturing variations include semi-batch (i.e., fed-batch) manufacturing, as found in wet granulation, tablet coating, and fermentation, in which materials are added during processing and discharged at the end of processing. In semi-continuous manufacturing, materials are simultaneously charged and discharged, but for a discrete time period. Examples include roller compaction, tablet compression, and encapsulation. For semi-continuous manufacturing processes, the process output is independent of batch size as long as the material input is set up to produce consistent output as per the controlled process. Therefore, a fixed batch size is not required for semi-continuous manufacturing processes.

Regulatory guidances provide clarity on batch requirements. FDA’s Guidance for Industry: Immediate Release Solid Dosage Forms Scale Up and Post Approval Changes (2) outlines the  maximum allowable batch size as 10 times the size of the pilot/bio batch. FDA’s cGMP guidance 21 Code of Federal Regulations 210.3 (3) provides clarity on batch and lot definitions. A European Medicines Agency (EMA) draft guideline on manufacture of finished dosage forms (4) notes that the batch size for a product to be marketed should normally be compatible with qualified equipment. It should be sufficient enough to allow process capability to be established. For example, a commercial batch size for solid oral dosage forms should be at least 100,000 units unless justification is provided. The equipment capacity and maximum quantity allowed determines the maximum batch size.

Advantages of small batch sizes

Operational efficiency increases with use of smaller batch sizes for such semi-continuous operations as compaction, tablet compression, and encapsulation. Taking the product out faster achieves higher asset and line capacity utilization. Having a minimum possible batch size can also increase supply chain velocity. Examples of unit operations that are not affected by having non-standard batch size include: particle size reduction, fluid-bed drying, roller compaction, extrusion, tablet compression, and encapsulation (5).

FDA’s 2015 guidance on emerging technology (6) promotes adoption of continuous manufacturing technology, and the recent approval of tablet production on a Janssen continuous manufacturing line highlights regulators’ acceptance of continuous manufacturing, as long as product quality is maintained. Traditional tablet compression and encapsulation operations are semi-continuous manufacturing operations, which implies that the same duration for the tablet compression or encapsulation run should yield similar quality product. The following sections discuss approaches for determining and provide justification for an appropriate minimum batch size for semi-continuous dosing unit operations, such as tableting and encapsulation.

Determining consistent quality

Control strategies for tablet compression and encapsulation manufacturing include in-process quality control specifications for such quality attributes as tablet weight, hardness, thickness, friability, and disintegration time. These attributes should be measured frequently (i.e., at intervals of 15 or 30 min.) throughout the run. The quality attributes are guaranteed through the compression run by force control established during product set-up. Any tablet compressed beyond the upper and lower limits of the set main compression forces will be rejected. For both tablets and capsules, 100% or frequent weight sorting/check are also used to assure product quality over the entire run.

Powders, however, exhibit complex behavior during processing. The internal dynamics of powder systems under dosing are specific to a product. The start and end fraction samples are considered “worst case” and are indicative of segregation issues that may occur during a routine manufacturing process. Solid-dose tablet compression/encapsulation processes do not typically include purging as a control strategy to reduce segregation risk. Therefore, along with the stratified process validation (PV) Stage 1 content uniformity data, the content uniformity results from PV Stage 2 batches provide a clear indication of homogeneity. Typically, stratified samples are collected from across the dosing run from 20 locations to verify consistency and reproducibility throughout the batch, and replicate samples are tested for uniformity per location. The unit dose is also tested to confirm product-specific physical and chemical quality attributes (see Table I). In addition to content uniformity, active ingredient homogeneity is evaluated in powder blends (i.e., blend uniformity) in all products at each batch size and bin size at Stage 2. The drug-content uniformity is determined by blend uniformity, stratified dosage uniformity, and assay. In-vitro performance of the dosage form is assured by dissolution testing. Based on the assurance of multi-component uniformity and in-vitro performance, it can be concluded that a semi-continuous tablet compression/encapsulation process is capable of producing consistent unit doses with any dosing batch size.  

Dosage formPhysical testsChemical tests

Appearance, individual tablet weight, weight of 10 tablets, hardness, thickness, friability, disintegration 

Stratified dosage uniformity (minimum of 20 samples), assay, dissolution profile, product-specific certificate of analysis and submission requirements. 

Appearance, individual capsule weight, weight of 10 capsules 




Factors to consider

In a systematic approach to determine the minimum tablet compression batch size, the following factors can be considered: tablet weight, API percentage, manufacturing process, and set-up waste from similar products and/or processes. 

Tablet weight. The total run time for the dosing batch is based on the target tablet/capsule weight. For any assigned minimum batch size to be compressed, the products with minimum tablet weight will take more time to compress than products with maximum tablet weight. As per the Stage 2 stratified sampling, a total of 20 locations are sampled during the dosing run. Therefore, use of a minimum batch size can be evaluated with products of low and high unit weights. 

Robustness of unit dose weight uniformity. Tablet weight is typically monitored using force control mechanism throughout the tablet compression process, where rejection limits (S+ and S- rejection forces and M+ and M- adjustment forces) are defined. Any tablet outside the acceptable limits is rejected. Forces are specific to a tablet press model, although the concept is applied for all. Tablets or filled capsules can be subjected to weight check as well. Normally, higher tolerance limits for weight checking are maintained, which are tighter than the values in the master document.

API percentage. Low API % w/w in the formulation is considered a high risk factor due to potential segregation after final blend and a high risk for content uniformity. Therefore, a product with low unit weight and low API content can be selected to further evaluate the minimum tableting batch size. This factor can also be used to determine variability within a batch for a particular product. Data of comparable campaigns can provide a reasonable indication of the anticipated batch-to-batch variability. The magnitude of the batch-to-batch variability can be dependent on several different factors; one factor in particular is the API content or product label claim. To gain an understanding of batch-to-batch variability, historical dosage uniformity and dissolution data from a large number of campaigns (e.g., more than 200 Stage 2 campaigns encompassing over 700 individual batches and approximately 100 distinct molecules) can be compiled. The batch-to-batch variability can be extracted from each campaign by separating the intra-batch variability from the overall total campaign variability. The data can be then segregated and analyzed to assess the relative influence of several factors (e.g., manufacturing process, strength, batch size). Product active content or strength has a high probability to be a factor that correlates to batch-to-batch variability. Typically, batch-to-batch variability for both content uniformity (CU) and dissolution significantly increases for low-strength products (<1 mg). Thus, one relevant factor for batch-to-batch variability is active content or strength (7).

Manufacturing process. Another factor that affects the minimum required dosing batch size is the manufacturing process. For example, the potential for segregation is minimal with hot-melt extrusion processes, in which the API is formed into agglomerates by melting of liquid binders. A direct mix manufacturing process has a higher potential for API segregation than a compacted process wherein the API is locked into granules. Therefore, a product with low API content and low unit weight from a direct-mix manufacturing process and high API content and high unit weight from a granulation manufacturing process may be considered as extreme cases for the assessment. 

Start-up waste from similar product/process. Start-up waste is generated due to initial adjustments to achieve the in-process quality attributes (i.e., tablet weight, hardness, thickness, friability, and disintegration) prior to starting the compression process. Process performance qualification samples are collected after start up, where all the in-process specifications are achieved at an established consistent tablet-press speed. In-process quality attributes are maintained by the force-control mechanism throughout the compression process. Because the tablets manufactured as start-up waste are disposed of, the start-up waste generated should be considered for the minimum batch quantity requirement.

Based on these four factors, the product portfolio can be assessed and summarized as shown in Table II.

API % (w/w)Manufacturing processTablet weightMaximum start-up waste

CU results as is (min–max)

LowDirect compression Low<5



MedDirect compression Med<1






*D. Alsmeyer, et al., AAPS Pharm. Sci. Tech. 17 (2) 516-522 (2016).



The assessment is based on an underlying assumption that the equipment qualification and calibration tolerances of key parameters were considered, and that a compliant quality management system is in place to detect any adverse trends or deviations. Additional factors can be added to the assessment. A minimum dosing batch size can be assigned based on the factors (tablet weight, API percentage, manufacturing process, start-up waste) as well as equipment capacity/capability (e.g., hopper feeder, powder bowl capacities) and regulatory market requirements, with the underlying assumption that the product has an established control strategy. Application of a minimum batch size based on the described strategy is of low risk for the product with a defined manufacturing process from Stage 1: process design, confirmed at Stage 2: process performance qualification, continually monitored as part of Stage 3: continued process verification, and with a control strategy established, including in-process controls. Jana Spes, vice-president of Technical Operations, Apotex, summarizes that variable batch sizes for semi-continuous processes such as tablet compression and encapsulation, without compromising product quality, allows for operational flexibility and efficiency. With regulatory acceptance of continuous manufacturing technologies and the associated minimal impact of batch sizes, it is time to reconsider the approach to batch-size determination for traditional semi-continuous manufacturing processes as well.


  1. S. Chatterjee, “FDA Perspective on Continuous Manufacturing,” IFPAC Annual Meeting (Baltimore, MD, January 2012).
  2. FDA, Guidance for Industry: Immediate Release Solid Dosage Forms Scale Up and Post Approval Changes (Silver Spring, MD, November 1995).
  3. FDA, cGMPs (21 CFR 210.3(b)(2)) (Silver Spring, MD, April 2015).
  4. EMA, Draft guideline on manufacture of the finished dosage form (London, September 2015).
  5. FDA, Draft Guidance for Industry: Advancement of Emerging Technology Applications to Modernize the Pharmaceutical Manufacturing Base (Silver Spring, MD, December 2015).
  6. A. Pazhayattil, et al. AAPS Pharm. Sci. Tech. 17 (4) 829-833 (August 2016).
  7. P. Pluta, “Benchmarking” J. Validation Tech.

, accessed July 21, 2016.

About the Authors
Naheed Sayeed-Desta is manager, Process Validation,; Ajay Pazhayattil is associate director, Process Validation; and Srihari Chowdari is manager, Technical Operations, all at Apotex.

Article DetailsPharmaceutical Technology
Vol. 40
APIs, Excipients, and Manufacturing Supplement
September 2016
Pages: s16–s19

When referring to this article, please cite it as N. Sayeed-Desta, A. Pazhayattil, and S. Chowdari, "Determining Minimum Batch Size," APIs, Excipients, and Manufacturing supplement to Pharmaceutical Technology 40, 2016.