Small Molecules, Big Challenges: Adopting New Methods for Stability Testing

Introduction

Stability testing is one of the most important steps during the development of a pharmaceutical product. It requires a series of analyses to determine how long a product maintains the properties and characteristics it possessed at the time of its packaging. In other words, it assesses how long the quality of the product persists during storage, i.e., how stable it is. The effect of environmental factors on the efficacy, purity and structure of the product is evaluated over time to define its shelf life and proper storage conditions, which are included on the product labelling. The importance of such information is highlighted by the fact that stability testing data are required for a new drug or formulation to receive regulatory approval.

The stability of a pharmaceutical product has been defined as the capability of a particular formulation in a specific packaging system to remain within its physical, chemical, microbiological, toxicological, protective and informational specifications. It is dependent on a range of factors, including the stability of the active ingredient(s); interaction between active ingredients and excipients, exposure to light, heat and moisture, propensity for degradation by oxidation, reduction, hydrolysis or racemization, and storage conditions, such as pH, or the presence of radiation or catalysts.

Stability testing is thus a complex process as the effects of a variety of factors that may influence stability must be assessed. Physical changes to the pharmaceutical agent may be the result of impact, vibration, abrasion, temperature fluctuations such as freezing, thawing or shearing, microbiological changes or degradation reactions. Any of these could alter the action of the active pharmaceutical ingredient (API), thereby reducing its potency, or lead to the formation of toxic degradation products, which could give rise to adverse effects. In addition, the packaging may lose integrity over time, which may reduce the stability of the product it contains or even contaminate it.

Defining the stability of a pharmaceutical product is thus critical to ensuring patient safety and the desired clinical outcomes. If the potency of a life-preserving drug is reduced, the condition being treated will not be controlled and may lead to the death of a patient. Similarly, contamination with toxic degradation products or infectious agents could have life-threatening consequences.

Therefore, stability testing is a routine procedure performed on drug substances and products at each stage of product development so the company can be certain that the quality of their products will endure throughout the time they are available for supply to patients. There is increasing demand from both pharmaceutical companies and regulatory bodies for increasingly sensitive analytical techniques that can provide the highest possible assurance that a product is of acceptable quality and will provide the promised efficacy safely. In addition, pharmaceutical companies are keen to get their product to market as quickly as possible so rapid effective technologies are needed for accurate characterization so approval is not delayed by unforeseen stability issues, for example by the presence of impurities from degradation.

The International Conference on Harmonization (ICH) has long recognized the importance of stability testing in drug development and wants drugs to be made safer by having a well-defined stability profile. ICH was pivotal in the introduction of the regulatory requirement for all impurities to be identified and not exceed a specific pre-defined level in the final product. It is important for pharmaceutical companies to have the necessary analytical methodologies in place early in the development process so potential impurities are identified early on and are not a surprise at the time approval is sought.

This is achieved by stress testing, which involves exposing the product to harsh conditions and assessing the effects on the product and identifying the degradation products. In this way, potential stability issues can be predicted and tests for the associated impurities implemented into the production process. Consequently, analytical techniques are needed to characterize the product rapidly with a high level of accuracy, sensitivity and resolution. There is therefore an ongoing need for analyses that can reliably (and quickly) quantify a vast array of potential impurities, which may be present in minute quantities. Success in achieving the goal of developing new and safe medicines faster is highly dependent on the development of appropriate analytical methodologies.

This article will provide an overview of the methods currently being used to assess drug stability and describe recent advances in chromatography and spectrometry that could be adopted to speed up drug development while also improving the safety of new molecules.

References

• Bajaj S, et al. Stability Testing of Pharmaceutical Products. Journal of Applied Pharmaceutical Science 2012;02(03):129 138. http://japsonline.com/admin/php/uploads/409_pdf.pdf
• Pharmaceutical Stress Testing. Second edition, 2011. eds Baertschi SW, Alsante KM, Reed RA. https://books.google.co.uk/books?hl=en&lr=&id=sQnMBQAAQBAJ&oi=fnd&pg=PP1&dq=define+forced+degradation&ots=jiT0ozJ8pb&sig=AeHtU1w-sG-KVbTVtvIrygNJsUQ#v=onepage&q=define%20forced%20degradation&f=true

Chapter 1 – Assessing Drug Stability

A stability-indicating test is a validated quantitative analytical method that can detect changes over time in the chemical, physical or microbiological properties of a drug substance during storage. It must be specifically tailored for each drug product so that the content of active ingredients and degradation products can be accurately measured without interference. Stability-indicating assays must be able to effectively separate each and every degradation product so that each can be individually analyzed. Other considerations include ensuring mass balance is maintained, conducting stress testing of new formulations, and acknowledging the potential for additional effects in combination products.

Stability-indicating methods are critically important for ensuring the well-being of patients who receive the pharmaceutical product. Both the presence of toxic degradation products and the loss of efficacy can have fatal consequences. Reduction in drug activity to a level of 85% of that claimed on the label may lead to failure of the therapy to have the required effect. For some drugs, such as nitroglycerine tablets for angina and cardiac arrest, such a loss of efficacy could result in death. The realization of the potential for such outcomes as a result of product degradation led to the introduction of the legal requirement to provide evidence of the robustness of stability tests in order to obtain approval of a new product.

Full details of the methodologies used for stability-indicating tests must be provided before a drug can receive marketing approval. Licensing applications must include details of the techniques used to ensure that the identity, strength, quality, purity, and potency of the drug substance and drug product meet the prescribed standards. In addition, data must be provided to prove that these techniques meet proper standards of accuracy, sensitivity, specificity, and reproducibility and are suitable for their intended purpose. A laboratory assessment may also be conducted as part of the approval process to confirm that the analytical procedures are acceptable for quality control and suitable for regulatory purposes.

The current stringent regulations regarding stability-indicating assays mean that many existing methodologies are no longer adequate. Since there is no single assay or parameter that can characterize complex pharmaceutical products, the manufacturer is required to propose a stability-indicating methodology that provides assurance on the detection of changes in identity, purity and potency of the product. For each new product or formulation a company develops, they must follow a systematic method development process to identify an analytical strategy that will satisfy regulatory requirements. Development of a suitable stability-indicating test requires early identification of specificity, linearity, limits of detection (LOD), limits of quantitation (LOQ), range, accuracy, and precision to ensure the robustness of the methodology. Such analytical method validation is essential to demonstrate that an analytical procedure is suitable for its intended purpose.

Typically, seven key steps are required in the development of stability-indicating assays that would meet the regulatory requirements: critical study of the drug structure to assess the likely decomposition route(s); collection of information on physicochemical properties; stress testing; preliminary separation studies on stressed samples; final method development and optimization; identification and characterization of degradation products and preparation of standards; and validation of analytical methods. If these steps are followed, it should ensure that the method developed will determine and assure the identity, potency and purity of ingredients, as well as those of the formulated products. Not only will such a strategy meet regulatory requirements, it is also in the interest of the pharmaceutical company; obtaining a full understanding of a compound early in the drug development process will avoid time and money being invested in a product that is later found to have stability issues.

Stress testing is particularly important for predicting stability problems and identifying degradation products, which in turn define the analytical methods required for stability-indicating assays. Stress testing assesses the effects of the variety of factors with the potential to cause degradation. It involves extended exposure of the drug to conditions more extreme than would be normally be encountered, e.g., very high temperatures, extremes in pH and prolonged exposure to intense UV radiation. Generally, the aim is to achieve up to 20% degradation of the product to ensure that all potential degradation products are identified.

The capabilities of the analytical procedures used to assess the effects of stress testing are fundamental to their ability to provide assurance that the pharmaceutical product meets applicable standards of identity, strength, quality and purity during its shelf life. At Pittcon 2019, Kim HuynhBa of Pharmalytik will be discussing the importance of accuracy and precision in stress testing methodologies and the key aspects to consider in the development and validation of stability indicating methods in her presentation entitled “Key Factors to Develop Stability-Indicating Methods for Pharmaceutical Products”.

The trial and error approach of stress testing can be labor and time intensive, making it a costly process. Consequently, there was the need for a more targeted systematic approach. It has been shown that experimentation can be replaced with careful experimental design of forced degradation experiments, which reduces the associated cost and labour input required. A full factorial experimental design was used to determine optimum acid and alkali degradation conditions for chlorthalidone.

Similarly, a systematic protocol has been adopted in the development of a UPLC method for screening active pharmaceutical ingredients found in a common over-the-counter cough and cold medication. It includes scouting, screening, and optimization steps that systematically investigate chromatographic parameters. In her talk at Pittcon 2019, “Streamlined Method Development for Screening Active Pharmaceutical Ingredients in Cough and Cold Medication Using a Systematic Protocol”, Margaret Maziarz of Waters Corporation will detail how the systematic protocol enables quick development of reproducible and robust methods, which increases the chance of successful method validation.

Waters Corporation will be on site at Pittcon 2019 to discuss their latest advanced liquid chromatography solutions, including the ACQUITY UPLC H-Class PLUS liquid chromatography system, the next evolution of quaternary based ultraperformance instrumentation, that provides the highest resolution of any quaternary liquid chromatography system. In addition, their Empower™ 3 data software facilitates the acquisition, management, processing, reporting, and distribution of data acquired using ACQUITY.

Advion will be highlighting their AVANT Chromatography Systems that integrate the latest chromatography technologies with compact mass spectrometers. The flexible modular, stackable design of AVANT enables high performance chromatography equipment to be customized to meet a variety of analytical needs. Phenomenex will also be on hand at Pittcon 2019 to help you choose the right chromatography column from the latest additions to their portfolio.

At Pittcon 2019, Malvern Panalytical will be detailing their multi-detection Omnisec Reveal platform that combines light scattering and viscometry and can be used in conjunction with the Waters ACQUITY™ UHPLC system to provide faster and more detailed polymer analysis. Wyatt will also be available to discuss the first multi-angle light-scattering detector, μDAWN®, that can be used to directly determine absolute molecular weights and sizes of polymers, peptides, or proteins.

References

• Advion.https://advion.com/products/expression/hplc-uhplc-ms-for-chromatography/
• Alsante KM, et al. Recent Trends in Product Development and Regulatory Issues on Impurities in Active Pharmaceutical Ingredient (API) and Drug Products. Part 1: Predicting Degradation Related Impurities and Impurity Considerations for Pharmaceutical Dosage Forms. AAPS PharmSciTech 2013;15(1)

https://www.researchgate.net/publication/258955621_Recent_Trends_in_Product_Development_and_Regulatory_Issues_on_Impurities_in_Active_Pharmaceutical_Ingredient_API_and_Drug_Products_Part_1_Predicting_Degradation_Related_Impurities_and_Impurity_Conside

• Bajaj S, et al. Stability Testing of Pharmaceutical Products. Journal of Applied Pharmaceutical Science 2012;02(03):129 138. http://japsonline.com/admin/php/uploads/409_pdf.pdf
• Bakshi M and Singh S. Development of validated stability-indicating assay methods—critical review. Journal of Pharmaceutical and Biomedical Analysis 2002;28(6):1011 1040. https://www.sciencedirect.com/science/article/abs/pii/S073170850200047X?via%3Dihub
• FDA. Analytical Procedures and Methods Validation for Drugs and Biologics Guidance for Industry 2015. https://www.fda.gov/downloads/drugs/guidances/ucm386366.pdf
• Malvern Panalytical. https://www.malvernpanalytical.com/en/products/technology/ultra-performance-liquid-chromatography
• Phenomenex. https://www.phenomenex.com/Info/Page/lccolumns
• Sonawane S, et al. Development and Validation of Stability-Indicating Method for Estimation of Chlorthalidone in Bulk and Tablets with the Use of Experimental Design in Forced Degradation Experiments. Scientifica (Cairo) 2016;4286482. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4830733/
• Waters Corporation. http://www.waters.com/
• Wyatt. https://www.wyatt.com/products/instruments/udawn-multi-angle-detector-uhplc-sec-mals.html

Pittcon Tracks

Chapter 2 – Harnessing the Power of High-Performance Liquid Chromatography (HPLC)

After forced degradation in stress testing, it is important that the various resultant products are all totally separated for individual analysis. The separation is achieved using high-performance liquid chromatography (HPLC). A wide array of different HPLC techniques are available, many of which have been designed in the development of suitable stability-indicating methodologies. These include capillary electrophoresis chromatography (CEC) and super critical fluid chromatography (SFC).

The reversed-phase HPLC technique is probably the separation tool most widely used in forced degradation studies, since the degradation is typically carried out in aqueous solution. It provides an essential step that allows subsequent characterization and quantitation of the degradation products. Knowledge gained from the structure of the degradation products provides an insight into degradation pathways and the chemical properties and stability of the drug substance. It also enables the development of suitable analytical techniques to screen for impurities in the final product.

The separation power of HPLC was substantially increased in 2004 by elevating the pressure applied to the chromatography column. This advanced technique, known as ultra-high-performance liquid chromatography (UHPLC), with its tremendous separation power is an invaluable tool in forced degradation studies. Indeed, reversed phase UHPLC has been shown to provide a simple, economic, selective, and time-efficient stability-indicating methods for the determination of degradation products and impurities in pharmaceutical products.

However, with so many possible variations, UHPLC method development can be an arduous and time-consuming process, particularly when designing stability-indicating methods for complex drug products that must achieve full separation of all impurities, degradation products, excipients and active ingredients.

In a recent interview, Michael Dong of MWD Consulting offered advice on using UHPLC for method development in pharmaceutical analysis. He highlighted the value of UHPLC in facilitating efficient method development where rapid changes of mobile phase and operating conditions are required. Up to six columns with two mobile phases can be screened in a few hours using fast broad gradients. This provides an indication of which bonded phases and mobile phases would work best for the sample and forms the basis for further method development. He also explained how HPLC techniques can be converted to UHPLC using geometrical scaling.

At Pittcon 2019, in his presentation entitled “UHPLC in Method Development of Stability-Indicating Methods” Michael Dong will describe the use of UHPLC in the rapid development of ICH-compliant stability-indicating methods including approaches such as automated column/mobile phase screening, a 3-pronged method template approach, and a universal generic gradient methodology.

Advances over the last decade have enabled a tremendous increase in the separation performance achievable with liquid chromatography as well as a decrease in analysis time. Chromatography is no longer performed at modest pressures (100–200 bar), using long bulky columns with relatively large fully porous particles. Instead, effective separation is attained using short compact columns with small superficially porous particles operated at ultrahigh pressures (1200–1500 bar). The capacity for more powerful separation, however, does not obviate the need for a good knowledge of optimal chromatographic conditions in order to achieve the best results for a given separation. Optimum results depend on choosing the right instrument configuration. It may not always be necessary to make the conversion from HPLC to UHPLC. Sometimes separations can be quickly and effectively achieved through changes to the chromatography column. For example, to avoid losing pressure when switching to smaller particles or more superficially porous particles, a shorter column with a narrower internal diameter can be used. This also has the benefit of reducing solvent consumption. The performance of these low-volume columns is strongly affected by the extra column dispersion in the chromatographic system. Smaller and better particles, higher operating pressures, and reduced system contributions all play important roles in determining the performance of a chromatographic system.

Ken Broeckhoven of Vrije Universiteit Brussel will be giving a presentation at Pittcon 2019 entitled “Guidelines to Make Optimal Use of Ultra-High Pressures in Pharmaceutical Analysis” in which he will illustrate the importance of ensuring proper chromatography system configuration. He will show how to make the most of the advances in chromatography, and that for some applications using HPLC with a different particle type or column length will be more advantageous than a conversion to UHPLC.

Many suppliers of specialised chromatography instrumentation will be present at Pittcon 2019 to discuss the latest advances. Advion, Hitachi, ThermoFisher Scientific and Wyatt will be on hand to discuss how their HPLC and UHPLC solutions provide the high performance, high resolution, and high sensitivity needed in forced degradation studies. These include the Avant range, ChromasterUltra Rs and the innovative Vanquish UHPLC platform. In addition, Bruker will be highlighting the utility of their EPR spectrometers to detect short-lived free radicals in forced degradation studies.

References

• Advion. https://advion.com/products/expression/hplc-uhplc-ms-for-chromatography/
• Blessy M, et al. Development of forced degradation and stability indicating studies of drugs—A review. Journal of Pharmaceutical Analysis 2014;4(3):159 165. https://www.sciencedirect.com/science/article/pii/S2095177913001007
• Broeckhoven K, et al. Particles, Pressure, and System Contribution: The Holy Trinity of Ultrahigh-Performance Liquid Chromatography. LCGC Europe 2017;30(11):618–625. http://www.chromatographyonline.com/particles-pressure-and-system-contribution-holy-trinity-ultrahigh-performance-liquid-chromatograph-0
• Bruker. https://www.bruker.com/applications/pharma-biopharma/drug-development/stability.html
• Hitachi. https://www.hitachi-hightech.com/global/product_detail/?pn=ana-chromasterultra
• Ramesha B, et al. Development and Validation of a Stability-Indicating Gradient RP-UHPLC Method for the Determination of Impurities in Atorvastatin Drug Substance. Journal of Liquid Chromatography & Related Technologies 2014;37(3):275 297. https://www.tandfonline.com/doi/abs/10.1080/10826076.2012.745135
• ThermoFisher Scientific. https://www.thermofisher.com/uk/en/home/industrial/chromatography/liquid-chromatography-lc/hplc-uhplc-systems.html
• Wyatt Technology. http://www.wyatt.eu/index.php?id=348 / https://www.wyatt.com/products/software/astra.html

Chapter 3 – The Role of Multidimensional Chromatography

After separation by chromatography, various methods can be used to detect the different eluents. Although the UV detector is most commonly adopted, light-scattering and nuclear magnetic resonance spectroscopy (NMR) among others are becoming increasingly popular. Mass spectrometry (MS) may also be used to provide more in-depth structural detail. In this case, the mobile phase selected for HPLC should be MS-compatible, such as triflouroacetic acid and ammonium formate.

Peak purity analysis is also needed to verify that an impurity or degradation product does not co-elute with the drug. This is an important step for determining the specificity of the method and can be achieved using photo diode array (PDA) detection. The separation technique can then be optimized, for example by changing flow rate, injection volume, column type and mobile phase ratio, for separating closely eluting peaks. When degradants cannot be isolated in pure form, a combination of chromatographic and spectroscopic techniques is necessary, such as HPLC-photodiode array ultraviolet detector (DAD), LC–MS, LC–NMR, to compare addition physical properties rather than rely solely on the relative retention times.

In addition to these multi-modal chromatographic techniques, multidimensional chromatography can be used. This involves performing two (or more) different separation stages. Different chromatographic columns are connected in sequence, and the effluent from the first system is transferred onto the second column. Usually, different types of column or conditions will be used in the different stages. In this way eluents that are poorly resolved by first column may be completely separated in the second column. Thus the superior resolving power of multidimensional methods over single-dimension approaches enables comprehensive separation of complex biological mixtures, with excellent resolution and reproducibility. It overcomes the problem of co-elution, poorly retained peaks, impurities without UV chromophores, and strongly retained components.

Multidimensional chromatography is also particularly useful for the separation of drugs containing a chiral center or a center of unsaturation, for example many antidepressant and antipsychotic drugs. The separation of chiral compounds is particularly challenging as the compounds have the same composition and molecular weight. They differ in the arrangement of atoms making them asymmetric in such a way that the structure and its mirror image are not superimposable. This difference in stereochemistry can significantly alter pharmacodynamic and/or pharmacokinetic properties and so it is important that each individual enantiomer is investigated early in the drug development process. In some cases, the enantiomer of the intended drug may not provide the required therapeutic effect, whereas in others it may enhance or augment the desired effect. The increased resolution and sensitivity of multidimensional chromatographic separations makes them more suited to the detection of multiple chiral centers then UHPLC alone. Coupled with MS, the separated enantiomers can also be reliably identified.

A multidimensional strategy provides an efficiency that surpasses traditional peak capacity and orthogonality. Consequently, it has been the focus of much research prompted by the need to separate increasingly complex pharmaceutical compounds. Significant advances in this area have developed multidimensional chromatography into a critical tool for tackling the challenges that cannot be resolved using one-dimensional chromatography.

The use of multidimensional liquid chromatography (MDLC) as a novel strategy for characterizing new drug entities without the need for method development will be discussed by Kelly Zhang of Genentech in her presentation at Pittcon 2019 entitled “Recent Advances in Multidimensional Liquid Chromatography for Pharmaceutical Analysis”. She will also present various strategies for implementing MDLC to resolve pharmaceutical analytical issues, including the separation of compounds with multiple chiral centers.

Thermo Fisher Scientific will be on site at Pittcon 2019 to illustrate how rapid gradients on complex mixtures can be achieved for quantitative applications with high accuracy and resolution using their The Tempo™ nano MDLC. The system provides high performance, reliable, multi-dimensional liquid chromatography with high peak resolution and reduced cycle times.

References

• Baker GB & Prior TI. Stereochemistry and drug efficacy and development: relevance of chirality to antidepressant and antipsychotic drugs. Annals of Medicine 2009;2002(7):537-543. https://www.tandfonline.com/doi/abs/10.1080/078538902321117742
• Guttman A, et al. Multidimensional separations in the pharmaceutical arena. Drug Discovery Today 2004;9(3):136 144. https://www.sciencedirect.com/science/article/pii/S1359644603029726
• Thermo Fisher Scientific. https://assets.thermofisher.com/TFS-Assets/CMD/manuals/Man-Installation-UltiMate-3000-Proteomics-MDLC-EN.pdf
• Zhang K, et al. Two-Dimensional HPLC in Pharmaceutical Analysis. 2013; December 27. https://www.americanpharmaceuticalreview.com/Featured-Articles/151949-Two-Dimensional-HPLC-in-Pharmaceutical-Analysis/

Chapter 4 – Choosing a Spectroscopic Technique

Spectroscopy is a non-destructive analytical tool that rapidly provides information about the identity and quantity of compounds present in a sample. It is thus ideally suited to the monitoring of pharmaceutical compounds for potency and purity to ensure patient safety. Indeed, spectroscopy is the analytical method of choice for stability testing and is conducted regularly throughout the production process to confirm the levels of active pharmaceutical ingredients (APIs) and impurities.

Spectral analysis is an essential tool for maintaining drug quality and safety and has become a world recognized method for pharmaceutical production analysis that meets global regulatory requirements. Spectroscopy is an FDA-approved method for the monitoring and stability testing of APIs. Traditionally, visual ultraviolet (UV-vis) spectroscopy was the analytical tool of choice, but in recent years near-infrared spectrometry (NIRS) has become increasingly popular in the pharmaceutical industry.

Development of libraries of infrared spectra for thousands of compounds has greatly facilitated the interpretation of NIRS spectral. Bio-Rad, the leading producer of high-quality spectral databases, including the KnowItAll IR Spectral Library that contains 264,000 spectra, will be at Pittcon 2019. In addition, Waters Corporation will be highlighting how their innovative Empower™ Software can enhance pharmaceutical quality control and stability testing by standardising data reporting and improving sample throughput for product release.

Following a series of regulation updates by the FDA, EMA and ICH to ensure rigorous control of drug quality, NIRS has been adapted for myriad novel applications for the development, monitoring, and control of pharmaceutical processes All steps in the process of pharmaceutical production are now supported by NIR methods.

NIRS, being non-destructive, is particularly useful for analysis the of dosage forms and allows individual tablets to be analysed with high accuracy. The conventional NIR region lies between 700 and 2500 nm and spectra arise from absorption bands with low molar absorptivity and have broad, overlapping peaks. It is primarily this low absorptivity that makes NIRS most suitable for the analysis of intact dosage forms. When quantifying tablet components, NIR has been shown to have less variability than UV–vis spectroscopy.

The development of very potent drugs posed challenges in the formulation and production of homogenous low-dose formulations. Sensitive and reproducible quality control analyses were required to assure the physical stability of the powder blend for production of tablets or capsules. To improve accuracy, the content uniformity quality control procedure was typically conducted on the contents of 20 tablets and a mean value derived. However, this still allowed considerable variation between individual tablets, and consequently the dose a patient received. Individual tablet or capsule assay is now mandatory for tablets containing less than 2 mg or 2% w/w of active drug.

The use of in-line spectroscopic analytics allows tablet contents to be monitored during production, whereby allowing for feed-back and feed-forward control to ensure overall product quality. At Pittcon 2019 Benoit Igne of GlaxoSmithKline will discuss the use of spectroscopic techniques, including NIRS, for in-line monitoring of pharmaceutical oral solid dosage forms in his presentation entitled “Progress and Challenges for Low Dose Monitoring of Pharmaceutical Formulations”.

Several producers of NIRS instrumentation will be onsite at Pittcon 2019 to discuss analysis strategies and the capabilities of their products. These include Thermo Fisher Scientific Scientific with the Antaris II FT-NIR Analyzer that is designed for on-line and in-line analyses, and Hitachi who produce the UH4150 UV-vis/NIR spectrophotometer with low stray light and low polarization characteristics.

Another technique that enables determination of active ingredient content of tablets during continuous manufacturing processes is Raman spectroscopy. In addition, this has been combined with optical imaging to form the methodology known as Raman microscopy. This is a powerful tool for providing detailed chemical information in both the spatial and spectral dimensions. As such, it has become the standard way for the pharmaceutical industry to achieve polymorphic characterization of active pharmaceutical ingredients. As mentioned previously, many drugs exist in multiple polymorphic forms with widely differing chemical and physical properties, including stability, apparent solubility, morphology, and bioavailability. Being able to ensure that a drug product only contains the correct form is thus a critical aspect of drug safety.

A supervised learning approach to dynamic sampling (SLADS) has recently been developed which reduces the imaging time for Raman microscopy analysis by enabling image generation from fewer data points. Due to the weak spontaneous Raman scattering, conventional Raman imaging typically requires a relatively long integration time to obtain a high signal-to-noise ratio. The SLADS algorithm analyses the preceding set of measurements and identifies the next most information-rich sampling location so fewer sampling points are needed. Integration of SLADS into the feedback for beam positioning enables fully autonomous control over the selection of location and data acquisition.

This system has been used to acquire chemical images of pharmaceutical materials with >99% accuracy from 15.8% sampling and showed a 6-fold reduction in measurement time compared with standard Raman spectroscopy. Furthermore, there was negligible impact on image quality. SLADS has the added advantage of being directly compatible with standard confocal Raman instrumentation. A member of the team at Purdue University who developed this breakthrough in Raman microscopy, Zhengtian Song, will be providing more information about the technique in his presentation at Pittcon 2019 “Accelerated Confocal Raman Imaging by Dynamic Sparse Sampling of Active Pharmaceutical Ingredients”.

At Pittcon 2019 there will be opportunity to learn more about leading Raman spectroscopy instrumentation direct from the producers. This includes B&W Tek’s STRam™ QTRam® portable Raman systems, Renishaw’s SynchroScan© for acquiring wide-ranging spectra from continuous scanning without joins, and Thermo Fisher Scientific’s DXR™2xi Raman imaging microscope.

References

• B&W Tek – http://bwtek.com/products/i-raman-pro-st/ and http://bwtek.com/products

/qtram/

• Bio-Rad. http://www.bio-rad.com/en-uk/product/ir-spectral-databases?ID=N0ZXNZE8Z
• Bodson C, et al. Comparison of FT-NIR 2015transmission and UV–VIS spectrophotometry to follow the mixing kinetics and to assay low-dose tablets containing riboflavin. Journal of Pharmaceutical and Biomedical Analysis 2006;41(3):783 790. https://www.sciencedirect.com/science/article/abs/pii/S0731708506000616
• Ciurczak E and Igne B. Pharmaceutical and Medical Applications of Near-Infrared Spectroscopy. Boca Raton: CRC Press, https://doi.org/10.1201/b17136
• Hitachi. https://www.hitachi-hightech.com/global/product_detail/?pn=ana-uh4150
• Kukkar V, et al. Mixing and formulation of low dose drugs: Underlying problems and solutions. Thai J. Pharm. Sci. 2008;32. https://www.researchgate.net/publication/267773413_Mixing_and_formulation_of_low_dose_drugs_Underlying_problems_and_solutions
• Li Y, et al. Method Development and Validation of an Inline Process Analytical Technology Method for Blend Monitoring in the Tablet Feed Frame Using Raman Spectroscopy. Anal. Chem. 2018, 90, 14, 8436 8444. https://pubs.acs.org/doi/pdf/10.1021/acs.analchem.8b01009.
• Renishaw. https://www.renishaw.com/en/synchroscan–25924
• Thermo Fisher Scientific. https://www.thermofisher.com/uk/en/home/industrial/spectroscopy-elemental-isotope-analysis/molecular-spectroscopy/near-infrared-nir-spectroscopy/near-infrared-pharmaceutical-analysis.html
• Thermo Fisher Scientific. https://www.thermofisher.com/uk/en/home/industrial/pharma-biopharma/drug-formulation-manufacturing/analytical-instrumentation.html
• Waters Corporation. http://www.waters.com/waters/library.htm?cid=511436&lid=134684189&locale=en_GB
• Zhang S, et al. Dynamic Sparse Sampling for Confocal Raman Microscopy. Anal Chem. 2018;90(7):4461–4469. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025898/#R1

Conclusion

There is the potential for drugs and their packaging to degrade over time. It is thus important for pharmaceutical companies to determine how long a product maintains the properties and characteristics it possessed at the time of its packaging. Defining the stability of a pharmaceutical product ensures that the patient receives the intended dose and is not at risk of ingesting toxic degradation products. Stability testing is thus critical to patient safety.

Stability testing exposes the product to extreme conditions and a series of analyses assess how long the product maintains quality. It is one of the most important steps of pharmaceutical development. A stability-indicating test must be able to accurately quantify changes in the chemical, physical and microbiological properties of a drug substance over time.

In addition, the pharmaceutical company must have assurance that every batch of a product they market contains the correct form and amount of the active pharmaceutical ingredient(s). Many drug compounds occur in different stereochemical forms, e.g., enantiomers, which can have significantly different pharmacodynamic and/or pharmacokinetic properties. The final drug product must contain only the intended form(s) of the drug that provide the required therapeutic effect.

With increasingly stringent regulatory requirements, introduced to ensure that a pharmaceutical product is of acceptable purity and will provide the promised efficacy safely, there is a need for increasingly sensitive analytical techniques that can provide the highest possible assurance of drug quality. The techniques must be able to effectively separate and characterise every individual component of a drug product.

This need has driven the development of many novel analytical techniques to facilitate the improvement of drug safety whilst maintaining a rapid transition from drug discovery to approval and marketing. In particular, there have been many recent advances in chromatography and spectrometry methodologies that could be adopted further enhance the effectiveness of drug analysis.

The transition from high-pressure liquid chromatography (HPLC) to ultra-high-pressure liquid chromatography (UHPLC) provided significantly greater separation power. Capabilities have now been extended by the development of new solid phase materials that enable the rapid separation of complex mixtures in shorter columns. Furthermore, the practice of multidimensional chromatography in which a series of different chromatographic columns are connected in sequence and the effluent transferred from one system to the next. Each column enables greater separation of components with similar transition times. Multidimensional chromatography has proved especially useful for the separation of drugs containing a chiral center. Furthermore, multidimensional liquid chromatography strategies have been developed that can obviate the need for complex method development when characterizing new drug entities.

The separation of pharmaceutical ingredients is typically followed by detection and characterisation steps. To this end, the latest chromatography technologies have been integrated with spectrometers to determine structural features and light scattering detectors to directly determine absolute molecular weights. The choice of spectroscopic methodology has recently shifted from ultraviolet (UV) to near infrared (NIR). The preference for NIR spectroscopy is based on the capacity to analyse individual tablets with high accuracy and with less-important variability. There is the potential for NIR spectroscopy to be cost-effectively incorporated into pharmaceutical production lines so the quality of the drugs being produced can be screened in real time and changes made as needed.

Raman microscopy provides a powerful tool for achieving polymorphic characterization of active pharmaceutical ingredients. A supervised learning approach to dynamic sampling (SLADS) has recently been developed to speed up conventional Raman imaging. The SLADS algorithm identifies information-rich sampling locations so fewer data can be acquired whilst still producing high-quality images.

All these techniques, and more, will be discussed in more detailed during Pittcon 2019. The presentations and exhibits at Pittcon 2019 will thus provide insight into the analytical advances likely to further enhance pharmaceutical screening in the future. Visit the Pittcon 2019 guide to learn more about the symposia, oral presentations and short courses that will be taking place.

In addition, numerous market-leading providers of analytical equipment, products and services will be on-site at Pittcon 2019 to discuss the latest additions to their capabilities and address your specific analytical requirements.