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Dr. L. H. Hiranandani College of Pharmacy, Ulhasnagar
Design of experiments (DOE) is an efficient procedure for organizing research so that the resulting data can be analyzed to provide objective and meaningful findings. This systematic and organized strategy is used to determine the relationships between elements that influence a process and its eventual outcome. During these experiments, process variables or factors are deliberately adjusted to observe their impact on one or more response variables. As a structured approach, DOE is essential for evaluating how various components affect method outputs. Within the framework of mathematical modeling, DOE is widely utilized for implementing Quality by Design (QbD) in both industrial and academic research environments. Because it is considered the primary choice for rational pharmaceutical development, this review provides a detailed illustration of DOE methodologies.
Quality by Design
"Quality by Design" (QbD) is defined as a systematic developmental methodology that starts with established objectives. This framework prioritizes a deep comprehension of products and manufacturing workflows, alongside rigorous process control, anchored in scientific principles and quality risk management. [1]
Pharmaceutical organizations increasingly acknowledge the critical nature of product quality, safety, and efficacy. The implementation of QbD scientific methods has led to significant improvements in product quality. These methods offer clear, essential insights spanning from initial product design to final production, while QbD-based tools mitigate risks by enhancing both quality and operational productivity. Ultimately, the goal of pharmaceutical development is to create superior products and manufacturing processes that reliably yield intended performance outcomes.[2]
While the pharmaceutical sector has consistently prioritized quality, it has lagged behind other industries regarding manufacturing productivity and efficiency. Adopting a modern approach to drug development can enhance efficiency, offer greater regulatory flexibility and relief, and deliver substantial business advantages across the entire life cycle of a product. According to the ICH Q8 guidelines, the core principle of Quality by Design (QbD) is that quality should be inherent to the design process rather than merely tested into the final product.[3]
Element Of Quality By Design [4]
1. Quality Target Product Profile (QTPP)
2. Critical Quality Attributes (CQA’s)
3. Quality Risk Management
4. Design Space Development
5. Control Strategy
6. Product Lifecycle Management & Continual Improvement
This Article focuses on development of design space by implementation of design of experiments
Design Of Experiment (DOE):
Design of Experiments (DoE) is a systematic, organized methodology used to determine how various input factors (independent variables, xi) relate to one or more output responses (dependent variables, y) by establishing mathematical models, typically expressed as y = f(xi). This approach involves the deliberate and systematic variation of controlled input factors to observe their influence on outputs. Consequently, DoE facilitates the identification of the most critical factors, determines the optimal settings for achieving desired responses, and clarifies the interactions between different input variables. [5]
Choosing the most appropriate experimental design requires evaluating several criteria, including the specific research objectives, the total number of factors and interactions under investigation, and the statistical effectiveness and validity of the chosen design. To better understand their practical applications, these designs are generally categorized into two primary types[6]:
a) Screening Designs:
These are typically employed during the initial phase of a DoE study to pinpoint the most significant input factors while filtering out those that are negligible. Common examples include:
? Plackett-Burman
? Fractional Factorial
? Two-level Full Factorial
b) Optimization Designs:
These designs utilize three to five levels for each input factor, enabling the modeling of second-order (quadratic) response surfaces. Because they necessitate a larger number of individual experiments, they are generally reserved for studies involving a limited set of input factors. Key optimization designs include:
? Box-Behnken
? Central Composite Design
? 3-level Factorial
? Mixture designs
Application of Design of Experiment in Pharmaceutical Product Development
Factorial Design
Factorial design is a statistical research methodology designed to identify the interactive effects of every possible combination of variables within an experimental set. A full factorial experiment, also known as a fully crossed design, involves two or more factors where each factor is assigned discrete values or "levels". The experimental units in this design encompass all potential combinations of these levels across every included factor. [7]
By using this approach, researchers can evaluate how both individual components and their mutual interactions influence the response variable. In the majority of factorial experiments, factors are limited to two levels. A common example is a 2x2 factorial design, which involves two factors that each have two levels, resulting in four distinct treatment combinations. [8]
Table 1: Application Of Factorial Design in Pharmaceuticals
|
Type Of Formulation |
Independent Variables (Xs) |
Dependent Variables (Ys) |
Reference |
|
Methotrexate Loaded Chitosan Nanocarriers |
Levels Of Chitosan, Tripolyphosphate, Methotrexate |
Nanocarrier Formation, Particle Size, And Statistical Analysis |
[9].Teja, S. P. S., & Damodharan, N. et a.l(2018) |
|
Fluvastatin Loaded Solid Lipid Nanoparticles |
Lipid And Surfactant Concentrations |
Entrapment Efficiency and In-Vitro Drug Release |
[10]. Asif, A. H et. al. (2022) |
|
Hydrodynamically Balanced System Of Ketorolac Tromethamine
|
Amount Of Hydroxypropyl Methylcellulose K4M And Sodium Bicarbonate |
(Hardness), (FLT), Total |
[11].Dr. G. S. Asane et. al..(2023) |
|
Multi-Layer Tablet Containing Ticagrelor And Aspirin, |
Type Of Disintegrant Used In Ticagrelor Layer and The Type Used In Aspirin Layer |
Tablet Hardness, Disintegration Time, And In Vitro Drug Release |
[12].Mahmoud Mostafa, et. al. (2025) |
|
In Situ Gel Of Sumatriptan
|
Combination Of Xyloglucan |
Gel Strength Percentage Drug Release (After 8 H) |
[13].Kassab, et. al..(2023). |
|
Loratadine-Loaded Nanosponge
|
Concentration Of Lor:Ec Ratio And Stirring Rate |
Particle Size (Ps), In Vitro Release, Zeta Potential (Zp) And Entrapment Efficiency (Ee). |
[14].Sivadasan, D., et. al. (2024). |
|
Ibuprofen Fast-Dissolving Tablets |
Effects Of Ocimum Gratisimum Mucilage, Sodium Starch Glycolate, And Croscarmellose Sodium |
In Vitro Method, In Water Absorption, And Percent Drug Release At 5 Minutes. |
[15].Naik DCS, et. al. 2022. |
|
Emulsion |
Span 60 : Sodium Lauryl Sulfate Ratio, Organic : Aqueous Phase Volume Ratio, And Polymer Concentration |
Emulsion Phase Stability, Viscosity, And Conductivity |
[16.]Badawi MA, et. al. 2014 |
|
Lipid Based Nanoemulsifying Cilostazol |
Amount Of Oil (Capmul MCM), Amount Of Surfactant (Tween 80), And Amount Of Cosolvent (Transcutol HP) |
Globule Size, Span, Equilibrium Solubility Of Cilostazol, Zeta Potential, And Dissolution Efficiency, T30 Of Lipid Based Nanoemulsifying Cilostazol |
[17].Pund S et.al2014 |
|
Pellets For Oral Lysozyme Delivery |
Kneading Temperature, Impeller Speed, Liquid Addition, Extrusion Speed, Spheronizer Speed, And Spheronization Time |
Activity, Hardness, And Roundness Of Pellets For Oral Lysozyme Delivery |
[18].Sovàny T et.al. 2016 |
|
Nanostructured Lipid Carries |
Surfactant Concentration, Solid/Liquid Lipid Ration, And Ultrasonication Time |
Particle Size And Particle Size Distribution Of Nanostructured Lipid Carriers Containing Salicylic Acid For Dermal Use |
[19].Kovács et. al.., 2017)
|
|
Multifunctional Sunscreens |
Concentrations Of Ethylhexyl Triazone, Bemotrizinol, And Ferulic Acid In Multifunctional Sunscreens |
Antioxidant Activity, And Uva And Uvb Radiation |
[20].Peres et. al.., 2017)
|
|
Of Efavirenz Loaded Solid Lipid Nanoparticles |
Poloxamer 188, And Acetone To Methanol Ratio |
Particle Size, And Entrapment Efficiency |
[21]Raina, Kaur et. al. Jindal, 2017) . |
|
Gelling Microemulsion Of Lorazepam |
Oil To Surfactant/Cosurfactant Ratio And Concentration Of Gellan Gum |
In Vitro Drug Release And Viscosity At Physiological Ph Of A Microemulsion Of Lorazepam Via Intranasal Route |
[22].Shah et. al.., 2017)
|
|
Miltefosine-Loaed Polymeric Micelles |
Hydration Temperature, Stirring Speed, And Stirring Time |
Polydispersity Index Of Miltefosine-Loaded Polymeric Micelles |
[23].Valenzuela-Oses et. al.., 2017)
|
Fractional Factorial Design
Due to limitations involving time and availability of resources, Complete Factorial designs have not always been possible to be conducted. In such cases, Fractional Factorial (FF) designs have been used [24]
A Fractional Factorial Design is characterized by the use of a specifically chosen subset of experimental conditions derived from a Full Factorial Design. Essentially, only a portion of the possible Full Factorial conditions are utilized. This methodology proves more cost-effective as it minimizes the total number of required experiments. However, this reduction in trials can lead to aliasing, where certain factor effects cannot be easily distinguished from one another. Consequently, the choice of fractionation level is dictated by the desired resolution: low-resolution designs typically focus on identifying primary effects while ignoring interactions, whereas higher-resolution designs are capable of detailing both main effects and their subsequent interactions. [25,26]
Table2:Application Of Fractional Factorial Design In Pharmaceuticals
|
Type of Formulation |
Independent Variable |
Dependent Variable |
Reference |
|
Pitavastatin SNEDDS |
The Types Of Oil, Surfactant, Co-Surfactant, And Their Concentrations |
Transmittance, Emulsification Time, And Drug Load, Were Selected As Responses Followed By Particle Size Along With Zeta Potential |
[27].Kuncahyo, I. et. al. (2019). |
|
Gold Nanoparticles |
Reducing Agent Type (Chitosan Or Trisodium Citrate), Concentration Of Reducing Agent (10 To 40 Mg), Ph (3.5 To 8.5), Temperature (60 To 100 °C), Agitation Time (5 To 15 Min), And Agitation Speed (400 To 1200 Rpm), |
Particle Size And Polydispersity Index |
[28].Jani, H et. al. (2025). |
|
Ranolazine Extended-Release Tablets |
(Fluid Uptake And Kneading Time) |
Dissolution |
[29].Jonna, S et. al.. (2023). |
|
Piroxicam Self-Nanoemulsifying Drug Delivery System (Snedds)
|
Type And Concentration Of Oil (Triacetin And Oleic Acid), Surfactant (Kolliphor El And Tween 60), And Co-Surfactants (Transcutol And Peg 400) |
Emulsification Time, %Transmittance, Droplet Size, And Drug Loading. |
[30].Adi Nugroho et. al..(2023) |
|
Fluid Bed Granulation |
Inlet Air Temperature, Air Flow Rate And Binder Spray Rate During The Sprying Phase |
Moisture Of Granules And Flow Through An Orifice Of The Granules Obtained By Fluid Bed Granulation |
[31].Lourenço et. al.., (2012)
|
|
Nanosuspension |
Indomethacin Concentration, Stabilizer Type, Stabilizer Concentration, Processing Temperature, And Homogenization Pressure |
Particle Size Distribution, Zeta Potential, And Physical Form (Xrd) Of Nanosuspensions |
[32].Verma et. al.., (2009)
|
|
Acetaminophen Immediate Release Tablets |
Time Of Dissolution, Volume Of Dissolution Media, Ph Of Dissolution Media, And Rotation Speed |
Amount Of Acetaminophen Dissolved During |
[33].Romero, Lourenço, et. al. (2017)
|
|
Gold Nanoparticles |
Reducing Agent Concentration, Stabilizer Type, And Temperature, Agitation Time (5 To 15 Min), And Agitation Speed |
Particle Size And Polydispersity Index |
[34].Jani, et. al..(2025) |
Central Composite Design
By incorporating both linear and quadratic variables, the Central Composite Design (CCD) mathematical framework creates a response surface model that accurately aligns with practical experimental results. Calculating variable coefficients within this model assists investigators in clarifying the specific connections between influencing factors and their resulting responses. This detailed integration of linear and quadratic components improves response prediction and optimization within the designated experimental boundaries, offering a comprehensive view of the various elements affecting the outcome. [35]
The primary objective of the CCD methodology is to efficiently examine how categorical and continuous variables impact a response while minimizing the total experimental trials required. This efficiency is attained by combining axial, center, and factorial points. Data generated through CCD yields high-precision predictions, and the technique has demonstrated significant success across numerous projects focused on the development and enhancement of pharmaceutical formulations. [36]
Table3:Application Of Central Composite Design In Pharmaceuticals
|
Type of Formulation |
Independent Variables (Xs) |
Dependent Variables (Ys) |
Reference |
|
Bosutinib Monohydrate Loaded Lipid Nanoparticles |
Particle Size (Ps) In Nm And % Drug Entrapment Efficiency |
Precirol Concentration (Ml) And Poloxamer 188 (Mg) |
37. Panigrahi D et. al..(2025) |
|
Novel Micelles Of Harmine
|
Hm Amount And Hydration Volume |
Encapsulation Efficiency (Ee), Drug-Loading Amount (Ld), Particle Size, And Polydispersity Index (Pdi) |
[38]. Bei, Y. et. al. (2013) |
|
Varenicline Tartrate Dispersible Tablet |
Percentage Of Crospovidone And Croscarmellose Sodium |
Disintegration Time And Wetting Time |
[39].Bhavani B et. al. (2024)
|
|
Sustained Release Tablets Of Gliclazide |
Conc. Of Karaya Gum Conc. Of Guar Gum |
Drug Release In 8hr, Drug Release In 14hr, Drug Release In 20hr, |
[40]. Danga Neelima et. al. (2025) |
|
Solid Dispersion Of Fluvastatin Sodium |
Polymer (W/W) And Surfactant Concentration (% W/V) |
T50% (Minutes) , Q90(%) And Percentage Drug Content |
[41]. Neelam Sharma Et.Al.(2022) |
|
Oro Dispersible Films |
Percentage Of HPMC, Percentage Of Glycerol, And Drying Temperature |
Thickness, Weight, Tensile Strength, Elongation At Break, Young’s Modulus, And Disintegration Time Of Oro Dispersible Films |
([42].Visser et. al.., (2015)
|
|
Enoxaparin Sodium Loaded Polymeric Microspheres |
Combination Ratio Of Eudragit®Fs-30d / Eudragit® Rs-Po, Pva Concentration In External Phase, And Nacl Concentration On External Phase |
Size Of Microspheres, Encapsulation Efficiency Of Enoxaparin Sodium, Percentages Released Over 24h In Gastric, Duodenal And Colonic Media |
[43].Hales et. al..,( 2017)
|
Box–Behnken designs (BBDs)
Box-Behnken designs (BBDs) represent a highly efficient class of second-order response surface methodologies specifically engineered to gather extensive data on experimental error and variable influences while minimizing the required sequence of runs. When compared to the frequently utilized Central Composite Design (CCD), BBDs demonstrate superior rotatability and symmetry, often providing exhaustive insights through fewer experimental iterations. These designs are structured to operate across three distinct levels—coded as -1, 0, and +1—making them particularly suitable for complex investigations that involve between 3 and 21 independent factors. A notable feature of BBD is its ability to integrate both numerical and categorical factors during the optimization process; however, investigators should be aware that the inclusion of categorical variables generally leads to a proportional increase in the total number of experimental runs needed to maintain statistical validity. Furthermore, because BBDs do not contain combinations where all factors are at their highest or lowest levels simultaneously, they are often preferred for experiments where extreme physical conditions might lead to failed trials or unsafe processing environments. [44]
Table4: Application Of Box–Behnken designs In Pharmaceuticals
|
Type Of Formulation |
Independent Variables (Xs) |
Dependent Variables (Ys) |
Reference |
|
Hexatriacontane-Loaded Transethosomal Gel |
Lipoid (Mg), Ethanol (%), And Sodium Cholate (Mg) |
Particle Size (Nm), Polydispersity Index (Pdi), And Entrapment Efficiency |
[45]. Aodah A et.al (2023) |
|
Nanoemulgel For Azithromycin |
Tto Concentration, Surfactant Concentration, |
Globule Size, Polydispersity Index (Pdi), And Viscosity. |
[46]Iman S. et.al .(2026), |
|
Paliperidon Solid Dispersion |
Spray Rate, Atomization Pressure, And Inlet Temperature |
Compressibility Index, Particle Size, Solubility And Dissolution |
[47] R.K. Surawase et.al (2024) |
|
Albendazole-Loaded Zein Nanoparticles |
Concentrations Of Polyvinyl Alcohol, Acetic Acid, And The Weight Of Zein |
Particle Size, Polydispersity Index, And Zeta Potential. |
[48]Amina T. et. al., 2024, |
|
Release Modulating Matrix Systems Of Losartan Potassium |
Aminated Fenugreek Gum, Aminated Tamarind Gum And Aminated Xanthan Gum |
Burst Release In 15 Min, Cumulative Percentage Release Of Drug After 60 Min And Hardness |
[49]Shankar et.al. (2021) |
|
Extended Release Cefpodoxime Proxetil Chitosan-Alginate Beads |
Sodium Alginate Percentage, Chitosan Percentage, And Calcium Chloride Percentage |
Maximum Drug Encapsulation, Particle Size And Drug Release Of Cefpodoxime Proxetil Chitosan-Alginate Beads |
[50]Muftaba, Ali, Kohli, et.al. (2014). |
|
Aceclofenac Loaded-Nano Structured Lipid Carriers (Nlcs) |
Lipid, Lipid Oil, And Surfactand Phase |
Particle Size, Entrapment, Permeation Flux, And Percentage Release Of Aceclofenac Loaded-Nano Structured Lipid Carriers |
[51]Garg et. al.., (2017) Garg NK, |
|
Silymarin Nanoemulsion |
Amount Of Surfactant/Cosurfactant Mixture, Processing pressure and No. of Homogenization Cycles |
Globule Size, Size Distribution (Pdi), Percentage Transmittance, And Drug Release Of Silymarin Nanoemulsion |
[52]Nagi et. al.., (2017) |
Plackett–Burman Design
Plackett-Burman designs function as specialized resolution III, two-level fractional factorial frameworks. They enable the investigation of up to N-1 factors using N experimental runs, provided N is a multiple of 4. Typically implemented as an initial phase in Design of Experiments (DoE), these screening designs help identify critical input factors while eliminating those that are statistically insignificant. Because they focus on main effects, they are highly efficient for situations where a large number of variables need to be screened with minimal experimental trials.
While Pareto charts serve as effective instruments for this selection process by highlighting the most influential factors, they do not illustrate how changes in factor levels influence output responses. Instead, such insights into response behavior and the direction of the effect are better captured through the use of interaction and main effects plots. This design is particularly valuable in pharmaceutical development for studying the effect of formulation variables on drug release profiles, such as in hot melt sustained release extrudates. [53]
Table 5:Application Of Plackett–Burman Design In Pharmaceuticals
|
Type Of Formulation |
Independent Variables (Xs) |
Dependent Variables (Ys) |
Reference |
|
Dabigatran Etexilate Mesylate Immediate-Release Tablets
|
Pregelatinised Starch, Crospovidone, Microcrystalline Cellulose Ph 101, Talc, Magnesium Stearate, Hydroxy Propyl Methyl Cellulose, Hydroxy Propyl Cellulose And Lactose Monohydrate |
Release Of Drugs |
[54] Gaeade et. al.. (2021)
|
|
Betamethasone Suspension For Injection Formulation
|
Macrogol Type Concentration Of Polysorbate 80 (Mg/Ml) Concentration Of Carmellose Sodium (Mg/Ml) Filter Type Homogenization Time (Min) 6 Homogenization Speed (Rpm |
Particle Size Distribution , Viscosity , Sedimentation Time, Density , The Assay Of Benzyl Alcohol, The Assay Of Methyl Parahydroxybenzoate, The Assay Of Propyl Parahydroxybenzoate, The Assay Of Betamethasone Sodium Phosphate, And The Assay Of Betamethason Dipropionate |
[55] Yerlikaya, F et.al.(2023) |
|
Ivermectin Loaded Ethosomes |
Phospholipid Conc. ,Ethanol Conc. , Cholesterol Conc. , Organic Phase Composition Ethanol+Pg Ethanol+Ipa , Stirring Speed (Rpm) |
% Entrapment Efficiency % CDR |
[56] Ria N. (2024) |
Mixture Designs
Mixture experiments represent a specialized class of Design of Experiments (DoE) specifically applied in industrial and chemical fields where the relative proportions of ingredients, rather than their absolute quantities, influence a response variable. This is common in pharmaceutical and chemical formulation studies where components must sum to a constant total. In numerous practical scenarios, the experimental outcome is binary or dichotomous, such as a pass/fail result, which leads researchers to seek highly efficient and informative experimental designs to ensure statistical validity.
Relying on design suggestions derived from linear normal-theory models with constant variance can often be a simplistic or "naive" approach in these contexts. This study examines the inherent risks associated with such strategies by comparing them against D-optimal mixture designs specifically tailored for binary responses. Furthermore, it assesses the D-efficiency of various design options across different parameter subspaces to determine their robustness.
Conventional designs intended for normal theory models often prove inadequate for binary responses because they frequently prioritize boundary points of the experimental space. Conversely, D-optimal mixture designs for binary outcomes typically distribute design points in areas where the predicted response probabilities are of a moderate magnitude, providing more useful data for model estimation. It is strongly recommended that investigators carefully consider the known characteristics of underlying process models and the binary nature of the data when choosing the most suitable mixture designs for their specific applications. [57]
Table 6: Application Of Mixture Design In Pharmaceuticals
|
Type of Formulation |
Independent Variables (Xs) |
Dependent Variables (Ys) |
Reference |
|
SEDDS for Protein Kinase Inhibitor-Pazopanib Hydrochloride |
Labrafac WL1349, Labrasol, and Transcutol-P |
Solubility, precipitation after 15 min, and particle size |
[58] Amit Gupta et al., 2023 |
|
Herbal Mixture |
P. crispum M., C. sativum L., and A. graveolens L. |
DPPH free radical scavenging activity, total antioxidant capacity (TAC), and total phenolic content (TPC) |
[59] Nouioura G. et al., 2023 |
|
Nutraceutical Hard Candy |
Artemisia herba-alba Asso extract, 1.5 mL Glycyrrhiza glabra L. extract, and 1.5 mL Zingiber officinale extract |
Color, taste, flavor, texture, aroma, and overall acceptability |
[60] Souiy et al., 2023 |
|
Fruit Extract Capsule |
Extract of M. charantia and A. esculentu |
Fasting plasma glucose (FPG) |
[61] Peter E. L. et al., 2022 |
|
Matrix Tablets |
Carbomer (Carbopol® 971P NF) and Hydroxypropyl methylcellulose (Methocel® K100M or Methocel® K4M) |
Amount of TP released, release rate, and mechanism varied with carbomer ratio in total matrix and HPMC viscosity |
[62] Petrovic A. et al., 2009 |
|
Desonide-Loaded Emulgel |
Oil, Smix, and water |
Particle size, polydispersity index (PDI), zeta potential, % transmittance, and cumulative % drug release (CDR%) |
[63] Kaithwar et al., 2026 |
|
Erythropoietin in Nanoparticles |
Chitosan and pectin concentrations |
Particle size, polydispersity index (PDI), zeta potential, and entrapment efficiency |
[64] Nuryanti et al., 2026 |
CONCLUSION
In conclusion, the implementation of Design of Experiment (DOE) within the Quality by Design (QbD) framework provides a systematic and organized approach to pharmaceutical product development. By establishing robust mathematical models, DOE clarifies the intricate relationships between critical input factors and desired product quality attributes. This review highlights that the strategic selection of experimental designs—ranging from screening designs like Plackett-Burman and Fractional Factorial to optimization designs such as Central Composite Design, Box-Behnken, and Mixture designs—is essential for maximizing research efficiency. Ultimately, the application of these methodologies facilitates a science- and risk-based approach, ensuring the development of robust, high-quality, and efficient pharmaceutical products throughout their lifecycle.
REFERENCES
Reena Shinde, Dr. Nilesh Khutle, Implementation of Various QbD Designs in Pharmaceutical Product Development: A Critical Review, Int. J. of Pharm. Sci., 2026, Vol 4, Issue 6, 3132-3144. https://doi.org/10.5281/zenodo.20661292
10.5281/zenodo.20661292