INTRODUCTION:

As drug recalls, manufacturing failures, scale-up concerns, and regulatory constraints increase, the pharmaceutical sector continues to face significant challenges in ensuring the safety, quality, and efficacy of its products⁸. Product quality has always depended on end-product testing, which provides little insight into the underlying mechanisms¹. Regulatory agencies have promoted Quality by Design (QbD), a science- and risk-based methodology that prioritises process comprehension, variability reduction, and the application of robust control techniques, to address these gaps^2,3.

Quality by Design (QbD) aims to integrate quality throughout the entire development lifecycle, rather than relying exclusively on end-product testing^3,6. It is backed by programs including the FDA's cGMP modernisation (2002), Process Analytical Technology (PAT) guidance (2004), and ICH guidelines Q8, Q9, and Q10^32,33,38. QbD provides a systematic framework for integrating pharmaceutical development, risk management, and quality systems, resulting in consistent product performance^4,5.

This paper examines the principles, applications, and problems of QbD, providing a thorough review of its role in advancing pharmaceutical product development ^7,9. Figure 1 depicts the several stages of the pharmaceutical process lifecycle: define, design, characterise, validate, and monitor/control^11,26. Importantly, the final link between “monitor and control” and “define” reflects process changes that can be implemented based on improvement possibilities observed during process monitoring or to increase process resilience and performance^12,16. These adjustments re-enter the loop, ensuring a continual improvement strategy throughout the product's existence ²⁷.

Key Features of QbD:

· Provides a strategic tool for effective and productive drug development.

· Represents a flexible, theoretical, and systematic attitude.

· Based on the notion of designing quality into the process rather than testing it at the end.

· Applicable to both medicinal compounds and finished products (small molecules and biologics).

· It can also be used to build analytical methods.

· Can be implemented completely or gradually.

· Suitable at any stage of a product's life cycle.

· Regulators around the world support and promote the QbD approach ⁶.

Benefits of Quality by Design:

· Removes batch failures.

· Reduces deviations and costly investigations.

· Minimizes regulatory compliance issues.

· Improves manufacturing efficiency by lowering costs, rejections, and waste.

· Reduces the need for end-product testing, allowing faster release decisions.

· Integrates risk management into development and manufacturing ¹³.

· Creates a robust scientific knowledge base for all items.

· Enhances development and decision-making ¹⁴.

· Provides technical workers with greater process understanding.

· Encourages organizational learning as a future investment.

· Enhances communication with regulators and industry on scientific concerns.

· Provides consistent information and promotes ongoing improvement ³.

Opportunities in QbD:

· Create efficient, agile, and flexible systems that are adaptable to change.

· Increase manufacturing efficiency while lowering costs, rejections, and waste.

· Create a comprehensive scientific knowledge base relevant to all items.

· Improve communication with regulatory bodies and industry on scientific issues.

· Provide consistent and reliable information throughout the product life cycle.

· Apply risk management principles to product and process design.

· Encourage ongoing improvement by enhancing process understanding.

· Encourage innovation in product development and manufacturing ².

Key Elements of QbD:

Quality by Design (QbD), as defined in ICH Q8 (Pharmaceutical Development), is a systematic method of drug development. It prioritizes product and process understanding, risk management, and product quality rather than relying solely on end-product testing. The key pillars of QbD provide the foundation for ensuring consistent quality, safety, and efficacy throughout the product life cycle ³.

Quality Target Product Profile (QTPP):

According to ICH Q8(R2), QTPP is a prospective summary of a drug product's quality characteristics that must be met to assure intended quality, safety, and effectiveness. It is a strategic tool for drug development, with applications ranging from planning to regulatory communication, clinical and commercial decision-making, and risk management ^3,23.

QTPP identifies the quality features required for the product to provide the therapeutic benefit specified on the label consistently. It aids formulation scientists in developing effective strategies while keeping the development process focused and efficient ^6,7.

Typical QTPP elements for an immediate-release solid oral dosage form are:

· Tablet characteristics

· Identity

· Assay and content uniformity

· Purity/impurity

· Stability

· Dissolution

QTPP should only provide patient-relevant performance metrics. For example, tablet hardness and density may be relevant for process monitoring but are not covered by QTPP. If particle size affects dissolution, the QTPP should address dissolution rather than particle size itself ²⁵.

Labelling considerations related to QTPP include:

· Clinical pharmacology

· Indications and usage

· Contraindications

· Warnings and precautions

· Adverse reactions

· Drug abuse and dependence

· Overdose information

· Dosage and administration

· How supplied

· Animal pharmacology/toxicology

· Clinical studies

Fig.No.1: Quality by Design System³.

Critical Quality Attributes (CQAs):

After defining the Quality Target Product Profile (QTPP), the next stage in Quality by Design (QbD) is to identify the applicable Critical Quality Attributes (CQAs). A CQA is a physical, chemical, biological, or microbiological property or characteristic that must be maintained within a specific limit, range, or distribution to ensure the intended product quality ³. CQAs are typically connected with raw materials (drug substance and excipients), intermediates (in-process materials), and finished drug products ⁶. They are classified as a subset of the QTPP, namely those qualities that may be affected by formulation or process factors ⁷. For example, whereas QTPP comprises dosage form and strength (which remain constant during development), qualities such as assay, content uniformity, dissolution, and permeation flux are classed as CQAs since they fluctuate depending on process conditions ⁹.

CQAs are identified through risk assessment, as described in ICH Q9 ³². Prior product knowledge—such as laboratory discoveries, nonclinical and clinical experience, data from related compounds, and published literature—is critical in determining which features are important for safety and efficacy ². This systematic approach provides a scientific basis for relating a specific property to product quality ⁴.

Typical CQAs vary according to dosage form. For solid oral dosage forms, they include purity, strength, drug release, and stability ⁹. Parenteral products must ensure sterility and absence of particulate matter, inhalation products require appropriate aerodynamic properties, and transdermal systems depend on adequate adhesion performance⁵. Properties such as particle size distribution and bulk density may also be critical for pharmaceutical ingredients and intermediates, as they directly influence the final product quality ²⁴.

Fig.No.2: Decision Tree to Decide CQAs. ²

Risk Assessment in Quality Risk Management (QRM)

Quality Risk Management (QRM) is a systematic process for the assessment, control, communication, and review of risks that could impact the quality of a pharmaceutical product throughout its lifecycle. The initial list of parameters that may affect Critical Quality Attributes (CQAs) can be extensive, but Quality Risk Assessment (QRA) helps prioritise and reduce it through scientific evaluation^2,16.

Failure Mode and Effects Analysis (FMEA):

Failure Mode and Effects Analysis (FMEA) is a commonly used risk assessment tool in the pharmaceutical industry. It is a proactive and structured method used to identify possible failures in a process, material, design, or equipment and to evaluate their effects¹⁶. Each potential failure (failure mode) is assessed for probability (P) of occurrence, severity (S) of impact, and detectability (D) before it reaches the patient ¹⁸.

The Risk Priority Number (RPN) is calculated as:

RPN = P × S × D

with each factor rated from 1–5.

Low risk: RPN < 40

Medium risk: RPN 40–99

High risk: RPN ≥ 100

Higher RPN values indicate critical areas that require corrective or preventive actions.

Failure Mode, Effects, and Criticality Analysis (FMECA):

Failure Mode, Effects, and Criticality Analysis (FMECA) is an advanced form of FMEA that includes the evaluation of the criticality of each failure. It considers the degree of severity, probability of occurrence, and detectability of each failure mode ¹⁶. Criticality analysis translates these evaluations into a level of risk; if the risk is unacceptable, corrective actions are required ⁴. FMECA is useful for identifying failures in manufacturing processes, optimising maintenance, and strengthening control and quality-assurance procedures.

Fault Tree Analysis (FTA):

Fault Tree Analysis (FTA) is a top-down, deductive approach that starts with an identified product or process failure and systematically identifies possible root causes ¹⁶. The results are represented in a tree diagram showing logical relationships between faults. This tool is valuable for investigating deviations or complaints to ensure that corrective actions address root causes and do not introduce new problems ¹⁷.

Hazard Analysis and Critical Control Points (HACCP):

Hazard Analysis and Critical Control Points (HACCP) focuses on identifying, assessing, and controlling potential hazards—physical, chemical, or biological—in processes or products ¹⁶. The method involves hazard analysis, determination of critical control points (CCPs), setting critical limits, monitoring CCPs, and maintaining documentation²⁰. It helps demonstrate process understanding and control of quality-related and safety-related risks.

Ishikawa (Fishbone) Diagram:

The Ishikawa diagram categorises potential risks into broad areas such as Materials, Methods, Machines, Measurements, Environment, and People ¹⁷. It helps visualise and analyse the factors influencing product quality. For example, in a blending operation, content uniformity may be affected by raw material properties, processing parameters, equipment design, and environmental conditions.

Fig.No. 3: Ishikawa (Fishbone) Diagram. ¹⁷

Design Space:

The ICH Q8(R2) defines the design space as a multidimensional mix of input factors (e.g., material qualities) and process parameters that have been proven to provide quality². Working inside the design space does not constitute a shift. Leaving the design space is considered a change and typically requires regulatory permission³². The applicant proposes the design space, which must be assessed and approved by regulatory authorities. Design space can vary depending on scale and equipment¹⁸. A laboratory-scale design may not apply to a commercial-scale operation. Verifying the design space at the commercial size is necessary unless it is confirmed to be independent of scale²¹.

Fig.No.4: Schematic representation of the Design Space.²

Control Strategy:

According to ICH Q10, a control strategy is a planned set of controls based on current product and process information to ensure process performance and product quality¹⁶. Controls may include parameters for drug substances and products, facility and equipment operating conditions, process controls, completed product requirements, and monitoring techniques and frequency³³. Control strategies typically involve input material controls, process controls and monitoring, design space for individual or multiple unit operations, and final product specifications to assure consistent quality⁴. Quality testing ensures that finished medicinal items fulfil standards. Manufacturers typically conduct rigorous in-process tests, including blend consistency and tablet hardness²⁴.

Figure. 4 shows a QbD-based control technique for the blending process. To ensure pharmaceutical quality, formulation and production variables must be understood and controlled so that the completed product meets standards. End-product testing certifies the product's quality³.

Fig.No.5: Example of control strategy for QbD process. ⁴

TOOLS OF QUALITY BY DESIGN:

1. Design of Experiments (DOE):

Design of experiments (DOE) is a systematic approach to identifying the factors influencing process outputs. DOE trials can yield four to eight times higher returns in a shorter period of time. Using DOE in QbD allows for more information to be obtained with fewer experiments ¹⁷. In a pharmaceutical process, DOE considers raw material attributes (e.g., particle size) and process parameters (e.g., speed and time), while outputs include essential quality attributes including mix uniformity, tablet hardness, thickness, and friability. Experimenting with all of the input and output variables and process parameters for each unit operation is not feasible. DOE results can uncover ideal settings, essential factors influencing CQAs, and interactions and synergies between components (see Figure 8, Design of Experiments).

2. Process Analytical Technology (PAT):

The United States FDA defines Process Analytical Technology (PAT) as "a system for designing, analysing, and controlling manufacturing through timely measurements of critical quality and performance attributes of raw and in-process materials and processes, to ensure final product quality ²³." The primary goal of PAT is to improve process understanding and control, in accordance with the Quality by Design (QbD) principle that "quality cannot be tested into products; it should be built-in or by design" ³³.

Key Concepts and Goals of PAT:

· To maintain consistent product quality through real-time process monitoring and control.

· To reduce process variability while increasing manufacturing efficiency.

· To enable real-time release testing (RTRT) rather than traditional end-product testing.

· To encourage continuous improvement and support continuous manufacturing methods.

· To reduce batch failures and rework through early detection of process abnormalities²³.

Applications of PAT in Pharmaceutical Manufacturing:

· Blend uniformity monitoring

· Granulation process control (moisture content, particle growth)

· Drying process monitoring (end-point determination)

· Tablet compression (hardness, weight uniformity)

· Content uniformity and assay prediction

· Polymorphism and dissolution monitoring

· Particle size distribution analysis

· Real-Time Release Testing (RTRT) to replace or reduce traditional QC testing²³.

Advantages of PAT:

· Improved process robustness and product consistency

· Enhanced efficiency through reduced cycle time and material wastage

· Lower manufacturing costs due to reduced testing and rejections

· Enables automation and real-time decision-making

· Facilitates regulatory flexibility and supports continuous manufacturing²³.

1. Risk Management Methodology:

Quality Risk Management (QRM) is defined as “a systematic process for the assessment, control, communication, and review of risks to drug (medicinal) product quality across its lifecycle.” It is a critical component of the Quality by Design (QbD) framework and meets the regulatory requirements defined in ICH Q9 (Quality Risk Management). ¹⁶

Objectives of Quality Risk Management:

· To guarantee that product quality, patient safety, and regulatory compliance are maintained.

· To detect, assess, and minimize risks that may affect critical quality attributes (CQAs).

· To establish a scientific and systematic foundation for making process and control decisions.

· Creating a sense of control throughout product development and manufacture ¹⁶.

Steps in Risk Management:

1. Risk Assessment – Identify potential risks (process, equipment, materials) and evaluate their impact on product quality.

2. Risk Control – Implement actions to eliminate or reduce risks to an acceptable level.

3. Risk Communication – Share risk information and decisions among all stakeholders.

4. Risk Review – Continuously monitor and update risks based on new data or process changes ¹⁶.

Fig.No.7: Steps in Risk Management Methodology.¹⁶

Common Tool Used:

· Flowcharts and Checklists

· FMEA (Failure Mode and Effect Analysis)

· FMECA (Failure Mode, Effect, and Criticality Analysis)^21,22

· FTA – Fault Tree Analysis

· HACCP: Hazard Analysis and Critical Control Points

· PHA: Preliminary Hazard Analysis

· Risk Ranking and Filtering^2,16.

Benefits of Implementing Risk Management:

· Improves process understanding and product resilience.

· enables science-based decision-making.

· reduces batch failures and product recalls.

· Encourages regulatory flexibility through verified scientific rationale⁴.

· Supports continual improvement throughout the product's lifecycle¹⁶.

Challenges of QbD Implementation:

· Lack of process comprehension - Inadequate scientific knowledge of processes impedes QbD application.

· Internal misalignment entails insufficient coordination across R&D, manufacturing, quality, and regulatory teams.

· Uncertain business value - Uncertainty over the cost, timing, and return on QbD investment.

· Limited technology - Insufficient tools for data management and CQA comprehension⁹.

· Dependence on third parties: Difficulty implementing QbD with suppliers and contract manufacturers.

· Regulatory discrepancy - Various agencies interpret QbD differently¹⁵.

· Lack of explicit instruction - Regulators provide insufficient practical direction.

· Unprepared regulators - Some agencies lack the expertise to evaluate QbD-based submissions¹⁹.

· Unfulfilled regulatory benefits: Promised advantages are not clearly realised.

· International misalignment entails inconsistent QbD standards between countries²⁷.

CONCLUSIONS:

Quality by Design (QbD) is a modern, scientific, and risk-based approach to pharmaceutical product development and manufacturing. It changes the emphasis from end-product testing to a comprehensive understanding and control of processes^28,29. The proper application of QbD guarantees that quality is incorporated into the product from the start, resulting in consistent performance, increased efficiency, and regulatory flexibility. QbD promotes continuous improvement and innovation by defining the Quality Target Product Profile (QTPP), identifying Critical Material Attributes (CMAs) and Critical Process Parameters (CPPs), and implementing an effective control system. Ultimately, it helps patients with high-quality medicines, producers with fewer batch failures and better productivity, and regulatory authorities with greater assurance of product reliability^30,31. QbD is therefore a cornerstone of the future of pharmaceutical quality assurance and process optimisation.

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Received on 21.02.2026 Revised on 19.03.2026

Accepted on 10.04.2026 Published on 21.04.2026

Available online from April 24, 2026

Res. J. Pharma. Dosage Forms and Tech.2026; 18(2):147-154.

DOI: 10.52711/0975-4377.2026.00023

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