Taste Masking In Orally Disintegrating Tablets: Advanced Formulation Strategies, Evaluation Approaches, Artificial Intelligence And Regulatory Perspectives For Patient-Centric Drug Delivery

Orally disintegrating tablets (ODTs) are solid dosage forms which are designed to rapidly disintegrate in the oral cavity or dissolve upon contact with saliva, thereby enabling administration without the need for water. The ease of administration and rapid disintegration of ODTs make them advantageous for geriatric and pediatric patients and individuals experiencing difficulty in swallowing. ODTs can improve patient compliance and provide an alternative to conventional tablets and capsules for patients with swallowing difficulties ¹

Rapid disintegration of an ODT in the oral cavity presents a formulation challenge when the incorporated active pharmaceutical ingredient (API) has an unpleasant or bitter taste. Because the drug becomes available in the oral cavity during disintegration, bitterness can affect palatability and patient adherence. Therefore, taste masking plays a vital role in the development of the ODTs. Reported strategies include the use of sweetening and flavoring agents, polymeric coatings or encapsulation, drug-polymer complexation, and ion-exchange resins. The formulation of the bitter drugs is complicated by the low compression force, and structural porosity commonly associated with ODTs, which creates additional mechanical and formulation constraints²

Evaluation of ODT palatability remains an important aspect of formulation development. Conventional human taste assessment can be affected by variability among individuals and ethical limitations, particularly when pediatric formulations are evaluated, creating a need for alternative instrumental approaches. Taste sensors and electronic tongues have been investigated for the qualitative and quantitative assessment of bitterness and overall palatability, although these systems have their own limitations. Hence effective development of taste-masked ODT formulations requires consideration of both rapid disintegration in oral cavity and palatability, together with appropriate methods for evaluating taste performance.³

2. The Science of Bitterness: Receptors, Mechanisms, and Pharmaceutical Implications

2.1 Molecular Biology of Bitter Taste Transduction

Taste transduction involves α-gustducin and Gβγ subunits. It is initiated by TAS2Rs, a family of G protein-coupled receptors (GPCRs) activated by bitter ligands. The Gβγ complex is released and activates phospholipase C-β2 (PLC-β2), leading to the generation of inositol 1,4,5-trisphosphate (IP3) and release of intracellular Ca²âº. Increased intracellular Ca²âº activates TRPM4/5 channels, leading to membrane depolarization and activation of downstream ion channels that facilitate ATP release. P2X2/P2X3 receptors on afferent cranial nerves are then activated by ATP, producing signals that are transmitted to the gustatory brain and contribute to the perception of bitter taste. ⁴

Figure 1. Molecular mechanism of bitter taste transduction. [4,5]

 

Figure 2. Disease-stratified considerations for taste-masked ODT development across major therapeutic areas. [9–40]

Figure 3. Drug- and disease-specific formulation challenges influencing taste-masked ODT development. [10,11,17,21,23,27,34,40]

Figure 4. Key formulation challenges relevant to taste masking in ODTs. [40–57]

Figure 5. Taste-masking technologies used in ODT formulations. [34,52,58–69]

Figure 6. Complementary evaluation methods for taste masking in orally disintegrating tablets. [70–78]

6.1 In Vitro Dissolution-Based Taste Assessment

Despite its practical value, dissolution-based taste assessment has important limitations. Simulated salivary media cannot fully reproduce the physiological complexity of human saliva, including its composition, buffering capacity, and dynamic interactions occurring within the oral cavity. Furthermore, conventional dissolution methods cannot accurately replicate factors such as saliva flow, tongue movement, and swallowing, all of which influence drug dissolution and taste perception. Consequently, dissolution results should be regarded as an approximation of in vivo performance rather than a direct measure of human palatability. ⁷⁰

Another limitation is the lack of standardized experimental conditions across published studies. Differences in dissolution medium composition, agitation conditions, sampling time, apparatus, and approaches used to define bitterness thresholds make direct comparison of taste-masking performance difficult. Therefore, dissolution testing is best used as a preliminary screening method and should be complemented by instrumental techniques, such as electronic tongue analysis, and, where appropriate, human sensory evaluation. ⁷¹

6.2 Electronic Tongue Technology: Power, Limitations, and Future Perspectives

The reliability of e-tongue analysis depends on establishing a meaningful correlation between sensor responses and human taste perception. ⁶³ Although the technology offers objective and reproducible measurements, recent studies have emphasized that many pharmaceutical applications require more rigorous qualification and validation against sensory outcomes. ⁷² Consequently, e-tongue results should be interpreted primarily as comparative analytical measurements rather than direct indicators of patient-perceived palatability. ^72,73

In addition to validation challenges, e-tongues have several practical limitations. Sensor performance may be affected by membrane ageing, sensor drift, and calibration variability, which can influence long-term reproducibility. ⁷⁴ Furthermore, electronic tongues cannot fully reproduce the multidimensional nature of human oral perception, including attributes beyond basic taste, such as mouthfeel, texture, aftertaste, and overall preference. ⁷² Therefore, although e-tongues provide rapid and objective assessment of formulation differences, they cannot fully replace human sensory evaluation. ^72,74

Current evidence supports the use of e-tongues as valuable screening tools during formulation optimization, where they can reduce reliance on human taste panels in the early stages of development. ⁴⁶ However, whenever ethically and practically feasible, instrumental findings should be complemented by appropriately designed human sensory studies to confirm the relevance of taste-masking performance to human perception. ⁷³

6.3 Human Sensory Panel Evaluation: Gold Standard or Unreliable Benchmark?

Despite its importance, human sensory evaluation is subject to considerable inter-individual variability. ⁷⁵ Genetic polymorphisms affecting bitter taste receptors, particularly variants of TAS2R38, contribute to differences in bitterness sensitivity among individuals. ⁷⁵ Consequently, panel composition can influence study outcomes, highlighting the importance of appropriate participant selection and standardized sensory protocols. ⁷¹

Taste perception is also influenced by physiological factors, including saliva composition, salivary flow rate, and buffering conditions, which can alter drug dissolution and the perception of bitterness in the oral cavity. ^70,76 These sources of biological variability should be considered when interpreting sensory data and comparing results across different studies. ⁷⁰

Evaluation of pediatric formulations presents additional ethical and practical challenges because children should not be unnecessarily exposed to unpleasant or investigational formulations. ⁷¹ Consequently, pediatric taste assessment requires carefully designed study protocols, age-appropriate evaluation methods, and appropriate ethical oversight. ⁷¹ Instrumental methods such as the electronic tongue are therefore frequently used during early formulation screening, with human sensory studies reserved for confirmatory evaluation whenever appropriate. ⁷³

6.4 Emerging Bioassay Approaches: TAS2R Cell-Based Assays

Unlike dissolution testing or electronic tongue analysis, TAS2R cell-based assays provide receptor-specific information by identifying the bitter taste receptors activated by a particular active pharmaceutical ingredient (API). ⁷² They also enable mechanistic evaluation of taste-masking agents and bitter receptor antagonists by quantifying their ability to reduce TAS2R activation under controlled experimental conditions, thereby supporting the rational design of targeted taste-masking strategies. ⁷⁷

Despite these advantages, routine application of TAS2R bioassays remains limited by the need for recombinant cell culture facilities, specialized analytical instrumentation, and technical expertise. ⁷⁸ In addition, these assays evaluate receptor activation in simplified experimental systems and therefore cannot replicate the complex physiological processes involved in human taste perception, including the influence of saliva composition, oral processing, and inter-individual sensory variability. ^72,78 Therefore, TAS2R bioassays should be considered an additional mechanistic tool that complements human sensory evaluation in pharmaceutical taste-masking research rather than replacing it. ^72,78

7. Artificial Intelligence and Machine Learning in Taste Masking: Transforming ODT Development

7.1 AI-Driven Bitterness Prediction: From Molecular Structure to Formulation Decision

BitterDB, a curated database containing over 2,200 bitter compounds together with experimentally validated bitterness information and TAS2R annotations, has become an important resource for developing and validating computational bitterness prediction models. ⁷⁹ Machine learning models trained using curated datasets have demonstrated good predictive performance in distinguishing bitter from non-bitter compounds based solely on molecular structural features, enabling early identification of APIs that are likely to require taste-masking during formulation development. ⁸⁰

For ODT development, AI-based bitterness prediction can support formulation scientists by identifying compounds with a high probability of bitterness before laboratory evaluation. ⁸¹ This enables more informed selection of taste-masking strategies, reduces empirical formulation screening, and helps prioritize experimental resources during early formulation development. ⁸² Although computational predictions cannot replace experimental taste evaluation, they represent valuable decision-support tools that can improve the efficiency of pharmaceutical taste-masking research. ⁸²

7.2 Machine Learning for Electronic Tongue Data Interpretation

To overcome these limitations, machine learning approaches have increasingly been applied to e-tongue data analysis. Algorithms such as support vector machines (SVMs), artificial neural networks (ANNs), and other supervised learning methods can identify complex response patterns, improve sample classification, and enhance prediction of bitterness from multidimensional sensor data. ⁸¹ These approaches provide a more objective and robust interpretation of e-tongue measurements than conventional linear statistical methods, particularly during formulation screening and optimization. ^81,82

Recent advances in taste sensor technology, combined with improved chemometric analysis, have enhanced the quantitative assessment of bitterness and strengthened the role of e-tongues in pharmaceutical formulation development. ⁸² Although these systems cannot fully replace human sensory evaluation, they provide rapid, reproducible, and objective data that support formulation optimization while reducing reliance on sensory panels during early-stage development. ⁸³

Further progress in sensor technology, standardized testing protocols, and machine learning algorithms is expected to improve the reproducibility, predictive accuracy, and broader application of e-tongues in pharmaceutical research and quality assessment. ⁸³

7.3 AI-Optimized Formulation Development: Design Space Exploration at Scale

Conventional Quality by Design (QbD) approaches using Design of Experiments (DoE) provide a systematic framework for studying critical formulation variables. However, as the number of variables increases, the experimental workload and development time rise substantially. ⁸⁴ Machine learning approaches, including Bayesian optimization and active learning, can address this challenge by learning from initial experimental data and identifying the most informative experiments for subsequent optimization, thereby improving development efficiency while reducing experimental burden. ⁸⁵

Recent studies have demonstrated that AI-assisted optimization can reduce the number of experimental iterations required to identify optimized formulations compared with conventional trial-and-error approaches. ⁸⁵ By efficiently exploring the formulation design space, these methods can accelerate pharmaceutical development while maintaining product quality and performance. ^84,85

Future pharmaceutical formulation development is expected to increasingly integrate AI-based bitterness prediction, machine learning-assisted analysis of experimental data, and Bayesian optimization into unified decision-support workflows. ⁸⁴ Such approaches have the potential to support more rational and data-driven development of taste-masked ODTs by improving formulation screening, reducing experimental effort, and accelerating optimization. ^84,86 Successful implementation will depend on continued validation across different formulation platforms and close collaboration between pharmaceutical scientists, data scientists, and industry. ⁸⁴

8. Regulatory Perspective on Taste Masking and Palatability

Regulatory requirements for taste masking and palatability are currently addressed through broader requirements rather than through a single global guideline dedicated exclusively to taste masking. They encompass patient acceptability, age-appropriate formulation design and development, and product quality. Palatability is particularly important in pediatric drug development because poor palatability can affect medication acceptance and adherence. Recent literature continues to identify palatability as an important component of patient-centred pediatric formulation development and emphasizes the continuing need for scientifically justified taste-masking strategies. ^87,52

The FDA/ICH pediatric guidelines consider palatability and acceptability as crucial factors when pediatric medicines are considered. ICH E11(R1) states that orally administered pediatric medicines should be acceptable to children and recognizes taste masking as a formulation strategy that may be required to improve palatability. The guidelines recommend the use of age-appropriate dosage forms while considering the characteristics of the target pediatric population. ⁸⁷

The EMA Reflection Paper on Formulations of Choice for the Paediatric Population considers age-appropriate dosage-form selection and formulation acceptability in pediatric patients to be important. When selecting dosage forms for pediatric age groups, the taste and palatability of the medicine are important parameters. ⁸⁸

ICH Q6A provides guidelines for setting specifications, test procedures, and acceptance criteria for drug substances and drug products from a pharmaceutical quality perspective, but it does not provide a universal taste or palatability specification standard applicable to all pharmaceutical products. Therefore, palatability is evaluated based on the specific product and development environment rather than a single predetermined ICH acceptance criterion, as relevant to the targeted patient population and dosage form. ⁸⁹ Recent reviews describe pharmaceutical taste evaluation using multiple complementary approaches rather than a single recognized test, including sensory panels, dissolution-based methods, electronic tongues, and receptor/biosensor approaches. ^52,90

WHO guidelines discuss the appropriate use of taste-masking technologies in formulation development where necessary and describe parameters that affect pediatric acceptability of medications. More recent WHO material has also addressed taste masking and sweetening approaches for oral medicines. ^91,92

Collectively, the current regulatory and scientific literature indicates that palatability and taste masking are recognized as important components of patient-centred, particularly pediatric, formulation development, but there is no single globally harmonized taste-masking test, universal bitterness threshold, or numerical palatability acceptance criterion applicable across all pharmaceutical products. Recent reviews identify the lack of a standardized taste-assessment approach as an important barrier in pharmaceutical development. Therefore, developers should provide scientifically supported evidence demonstrating that the chosen formulation is suitable for its target patient population. Depending on the product, dosage form, development stage, and target population, this evidence may include appropriately designed sensory studies together with complementary instrumental and in vitro approaches. ^52,90

9. Emerging Technologies and Future Research Directions

9.1 Three-Dimensional Printing for Architecturally Precise Taste-Masked ODTs

A major milestone in pharmaceutical 3D printing was the 2015 U.S. FDA approval of Spritam® (levetiracetam), developed by Aprecia Pharmaceuticals, as the first commercially approved 3D-printed medicine. Manufactured using ZipDose® binder jetting technology, Spritam® demonstrated that highly porous tablets capable of rapid disintegration can be produced even at high drug doses, thereby establishing the regulatory feasibility of pharmaceutical 3D printing and stimulating further research into patient-centred oral dosage forms. ⁹³

Although clinical application of 3D-printed taste-masked ODTs remains limited, continued advances in printable pharmaceutical polymers, multi-material printing, computational formulation design, and personalized manufacturing are expected to facilitate the development of individualized ODTs with improved palatability, dose flexibility, and drug-release performance, supporting the broader implementation of precision medicine. ^94,95

9.2 Nanotechnology and the Next Generation of ODT Taste Masking

Although nanoparticle-based systems have demonstrated considerable promise for oral drug delivery, their application specifically as taste-masking technologies in ODTs remains an emerging area of research. ⁹⁰ Additional studies are required to establish formulation stability, large-scale manufacturability, regulatory acceptability, and clinical performance before widespread pharmaceutical implementation. ^90,52

9.3 Sensory Modulation Beyond Taste Masking: Bitter Taste Receptor Antagonism

Although receptor-targeted taste modulation represents an attractive future strategy, several scientific and regulatory challenges remain before clinical implementation. Bitter taste receptors are expressed not only in the oral cavity but also in extraoral tissues, including the gastrointestinal tract and respiratory system, where they participate in diverse physiological processes. ^96,97 Consequently, compounds intended to inhibit oral TAS2Rs may also influence extraoral receptor function, emphasizing the importance of comprehensive pharmacological and safety evaluation during pharmaceutical development. ^96,97

9.4 Personalized Taste Masking Based on Pharmacogenomics

Growing advances in pharmacogenomics and precision medicine have introduced the possibility of tailoring pharmaceutical formulations according to individual genetic differences, including variation in bitter taste receptor (TAS2R) genes. Human bitterness perception exhibits substantial inter-individual variability that is largely influenced by genetic polymorphisms in TAS2R receptors, particularly TAS2R38, which has been extensively associated with differences in sensitivity to bitter compounds. Other receptor variants, including TAS2R16 and TAS2R14, have also been implicated in variation in bitter taste perception, although their clinical significance remains under investigation ⁹⁸.

These genetic differences may influence patient acceptance of bitter medications and could eventually support the development of personalized taste-masking strategies. In the future, pharmacogenomic information may assist formulation scientists in selecting appropriate taste-masking technologies or optimizing formulation characteristics for individuals or specific patient populations exhibiting heightened bitterness sensitivity. However, the application of routine TAS2R genotyping for formulation design remains largely theoretical, and additional clinical and translational research is required before pharmacogenomics-guided taste masking can be incorporated into routine pharmaceutical practice ⁹⁹.

CONCLUSION

Taste masking in orally disintegrating tablets (ODTs) is not merely an organoleptic consideration but an important component of patient-centred formulation development. Although ODTs provide advantages for patients who experience difficulty swallowing, their rapid disintegration in the oral cavity can expose bitter active pharmaceutical ingredients (APIs) to taste receptors and consequently compromise palatability and medication acceptability. The clinical relevance of this challenge is particularly evident in pediatric, geriatric, dysphagic, and chronically treated populations, for whom repeated exposure to unpleasant-tasting medicines may negatively influence medication acceptance and adherence.

The evidence reviewed demonstrates that no single taste-masking strategy is universally applicable to ODTs. Ion-exchange resin complexation, polymeric coating and encapsulation, drug–polymer complexation, cyclodextrin-based systems, and the use of sweeteners and flavors each offer distinct advantages but may introduce formulation trade-offs involving drug loading, tablet size, disintegration, dissolution, mechanical strength, and stability. Consequently, taste-masking technology should be selected according to the physicochemical properties of the API, its bitterness threshold, the intended patient population, and the performance requirements of the final dosage form.

A major unresolved issue is the lack of standardized and universally accepted approaches for pharmaceutical taste assessment. In vitro methods, electronic tongues, human sensory evaluation, and emerging receptor-based assays provide complementary information, but differences in methodology and validation limit direct comparison between studies. Establishing a tiered and scientifically validated evaluation framework that integrates physicochemical, instrumental, and, where appropriate, sensory approaches would improve the reliability and reproducibility of taste-masking assessment.

Emerging artificial intelligence, machine learning, three-dimensional printing, nanotechnology, and receptor-based approaches offer opportunities to accelerate taste-masked ODT development and enable more rational formulation design. However, their broader application requires further validation, standardization, and integration with established pharmaceutical development and regulatory principles. Future research should therefore focus on developing formulation strategies that simultaneously optimize palatability, rapid disintegration, drug-release performance, manufacturability, stability, and patient acceptability, while regulatory efforts should move toward clearer and more harmonized expectations for pharmaceutical palatability assessment.

Overall, the future of taste-masked ODT development lies in an integrated, evidence-based and patient-centred approach that connects formulation science with clinically relevant palatability assessment, emerging computational technologies, and appropriate regulatory frameworks.

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