Near-Infrared Chemical Imaging and the PAT Initiative NIR-CI Adds a Completely New Dimension to Conventional NIR Spectroscopy

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Molecular Spectroscopy Workbench Near-infrared Chemical Imaging and the PAT Initiative NIR-CI adds a completely new dimension to conventional NIR spectroscopy.

E. Neil Lewis, Joe Schoppelrei, and Eunah Lee

Dear and gentle readers, this month I present an important other manufacturing steps have on the final dosage form? To tool in the process analytical technologies (PAT) initiative: encourage the PAT initiative FDA is streamlining the mecha- Near-infrared chemical imaging (NIR-CI). You might wonder nism for adopting new technologies in pharmaceutical manu- why I am seemingly concentrating on IR and NIR. The an- facturing. swer is quite simple: I need all the heat I can get, here in New York. Seriously, E. Neil Lewis, Joe Schoppelrei, and The Role of Near-infrared Chemical Imaging (NIR-CI) Eunah Lee of Spectral Dimensions (Olney, MD) have put to- A typical tablet is not just a pressed block of a single material, gether an excellent explanation of what NIR-CI is and what but rather a complex matrix containing one or more active its part in PAT is and will be. For those of you who do not pharmaceutical ingredients (APIs), fillers, binders, disinte- know Neil Lewis, he is one of the pioneers in IR and NIR im- grants, lubricants, and other materials. A basic problem in aging. He has won numerous awards for his research at the pharmaceutical manufacturing is that a relatively simple for- National Institutes of Health (NIH) and subsequent accom- mulation with identical ingredients can produce widely vary- plishments. It is truly exciting to have this paper in my hum- ing therapeutic performance depending upon how the ingre- ble column and I know you will find it informative and enter- dients are distributed in the final matrix. More potent APIs taining. can be formulated at dosages of 5 mg or less, but the finished tablet still must be large enough for convenient handling. In he US Food and Drug Administration (FDA) recently this case, maintaining content uniformity is even more cru- released a new guideline strongly advocating the use cial. Pharmaceutical makers also are developing advanced Tand development of new measurement technologies in tablets for drug dosage management, which can provide pharmaceutical manufacturing (1). The process analytical longer, flatter, or sometimes complex bloodstream profiles. technology (PAT) initiative, as it is known, promotes the use Approaches include the use of barrier layers, cored tablets, se- of techniques that enable the monitoring of critical process lective-release microspheres, and even osmotic pumps. These parameters during pharmaceutical manufacturing. The goal is tablets essentially are highly engineered drug delivery systems to not only enable process measurement but, more impor- in which the physical structure is as critical as the chemical tantly, to enable process understanding and ultimately process composition. optimization. Although FDA historically has focused on pu- Existing analytical techniques such as high performance rity and potency as its yardstick of product quality, in the fu- liquid chromatography (HPLC) and mass spectrometry (MS) ture more time will be spent trying to address issues dealing often are used to accurately determine the gross composition with physical processes. For example, what effects, if any, do of a dosage form, but they provide no information about the small changes in the blending, drying, pressing, coating, or distribution of the individual components. The manner and duration of component release is examined through dissolution testing. However, this provides no insight into the cause Emil W. Ciurczak of the profiles obtained. All of these techniques require de- works as a consultant with Integrated struction of the sample, making it difficult or impossible to Technical Solutions, 77 Park Road, Goldens trace the sources of failures or anomalies. Bridge, NY 10526. He can be reached via e- Spectroscopic techniques enable rapid, nondestructive mail at: [email protected]. analysis of samples and can be employed at a number of points in the pharmaceutical development and manufacturing process. In particular, NIR spectroscopy quickly is becom- ing a workhorse technique for the industry due to its high in-

26 Spectroscopy 19(4) April 2004 www.spectroscopyonline.com Molecular Spectroscopy Workbench

formation content and flexibility of im- around, and reducing time-to-market. sample. This is the fundamental concept plementation. It is used widely for the of chemical imaging: a rapid analytical characterization of raw materials, and Chemical Imaging Principles method that simultaneously delivers also has been used in applications such Conventional digital imaging is the spatial, chemical, structural, and func- as blend homogeneity, moisture meas- process of reproducing the spatial infor- tional information. urement, and the analysis of intact mation of a scene onto a two-dimen- The hypercube. Spectral images are tablets (2–4). sional optical detector. The typical visualized as a three-dimensional NIR-CI adds a completely new di- image recorded with a standard digital block of data spanning one wavelength mension (pun intended) to conven- camera or web-cam is collected across a and two spatial dimensions called a tional NIR spectroscopy. It offers the broad range of optical wavelengths, usu- hypercube (Figure 1). The hypercube ability to obtain high fidelity, spatially ally in the visible region, to produce a can be treated as a series of spatially resolved pictures of the chemistry of the grayscale image. Placing relatively resolved spectra (called pixels) or, al- sample. Elucidation of compositional broadband color filters in front of the ternatively, as a series of spectrally re- heterogeneity and structure is invalu- same detector produces a conventional solved images (called image planes or able for both the development and color image. On the other hand, a single channels). Selecting a single pixel will manufacture of solid dosage forms (5, spectral image usually is collected across yield the spectrum recorded at that 6). NIR images can be used to deter- a narrow wavelength range (very often particular spatial location in the sam- mine content uniformity, particle sizes, in the IR or NIR spectral region). It can ple. Similarly, selecting a single image and distributions of all the sample com- be used to reveal the chemical composi- plane will show the intensity response ponents, polymorph distributions, tion of the sample through absorption (typically scaled to color) of the scene moisture content and location, contam- by one or more chemical species within at that one particular wavelength. inants, coating and layer thickness, and the sample of that particular diagnostic Data analysis. The ultimate goal of the a host of other structural details (7–9). wavelength. The result is a spatially re- experiment is to generate highly specific Through the development phases of solved chemical map of the sample. chemical contrast in an image to visual- preformulation and scale-up, NIR-CI Chemical, or hyperspectral, imaging is ize and identify the compositional het- can be used to identify precisely the elu- the acquisition of images across a larger, erogeneity within the sample. Analysis sive critical control parameters that will usually contiguous series of narrow of the hypercube to produce this con- affect the performance of the finished spectral bands comparable to tradi- trast can be accomplished at several dif- product. The technique is fast and non- tional (single-point) spectroscopic tech- ferent levels. In some cases simply se- destructive and can be used independ- niques, thus integrating the complete lecting the image plane at a wavelength ently or in concert with other tech- spatial and chemical information of the of a characteristic band from a species niques, such as dissolution analysis, to rapidly diagnose potential production problems. NIR-CI instrumentation also is rugged and flexible, suitable for both λ the laboratory and the manufacturing environment. Therefore, analysis methods developed in the laboratory often can be tailored for implementation near-line or at-line. NIR-CI also is mas- yψ sively parallel NIR spectroscopy, making the technique well-suited for high λ λ × λ Spectrum: from 1 to k at (x i, y i) Image plane: n m pixels at j throughput at-line and even on-line ap- x x plications. Imaging also can represent significant economic benefits to the pharmaceutical manufacturer. “Blind” manufactur- Single-pixel spectrum ing processes produce products that can be tested only after the fact. Traditional analytical techniques usually are, in Single-channel image many cases, unable to pinpoint the sources of defects and failures in a timely fashion leading to costly delays. NIR-CI provides chemical and physical information at return rates that are Figure 1. Schematic representation of a spectral imaging hypercube showing the relationship faster than those of any other existing between spatial and spectral dimensions. technique, improving testing turn-

28 Spectroscopy 19(4) April 2004 www.spectroscopyonline.com of interest will readily indicate the spa- application of conventional multivariate spectra. In 1988, Harthcock and Atkin tial distribution and abundance of that quantitative methods in which individ- (14) published the first chemical maps material. However, this univariate ap- ual pixel spectra are analyzed using cali- collected with an Fourier-transform IR proach of data interrogating is quite bration data sets and techniques such as (FT-IR) microscope fitted with a mov- wasteful of the total information con- PLS. Again, access to the right software ing stage, demonstrating the concept of tent of the complete hypercube. tools that provide a variety of options is spatially localizing chemical species Most chemical images comprise important when attempting to imple- using infrared spectroscopy. many thousands of pixels and each pixel ment the best processing scheme for a During the past 15 years, great im- represents a full spectrum. Therefore, given experiment or sample. provements in optical designs and com- these data are well suited for multivari- puter and automation technology have ate (chemometric) analysis techniques The Dawn of Infrared occurred; thus, IR and Raman mapping such as principal component analysis Chemical Imaging instruments have become almost com- (PCA), principal component regression Spatially resolved spectroscopy — mapping. monplace in most well equipped re- (PCR) and partial least squares (PLS) The concept of spectral imaging can be search laboratories. However, many of modeling (10, 11). These methods use applied to almost any optical spectro- these instruments still utilize a moving the full spectral range and can distin- scopic technique. IR, Raman, fluores- sample stage and the step-and-acquire guish subtle, but real, chemical varia- cence, UV/Vis, and NIR spectral imag- acquisition mode. IR mapping instru- tions, even for complex samples. Conse- ing instruments currently are available. ments are limited to this method by quently, data analysis and software are However, chemical imaging has been their detectors’ configurations, which the key components in producing a suc- generally, but not exclusively, coined to are capable of collecting data from only cessful experiment or method. Ideally, refer to vibrational spectroscopic imag- a single point. They are, by design, un- the analysis tools must be designed ing approaches (IR, NIR, and Raman) able to capture an image the same a specifically to handle large hyperspec- which offer the high chemical selectivity manner as a camera. tral data sets, and should incorporate a necessary to distinguish a wide range of The infrared focal-plane array. Unlike complete set of image and spectral pro- materials. Historically, the first spatially mapping, infrared chemical imaging re- cessing options, as well as chemometric resolved IR spectra appeared in Nature lies on the use of a two-dimensional de- analysis procedures and image visualiza- in 1949, which described the use of a tector array. By way of contrast, the typ- tion options. Several software options microscope coupled with an IR spec- ical visible spectral range digital camera are available (12). trometer (13). However, this was not an uses a two-dimensional charge-coupled Although the prospect of using imaging instrument because it was lim- device (CCD) or complementary metal chemometric analysis techniques for ited to the collection of single-point IR oxide semiconductor (CMOS) array. At routine processing of hyperspectral data might, at first blush, seem daunting, in fact the ability to work with large sam- Large-Format infrared focal ple sets can improve the statistical relia- plane array (FPA) bility of the results significantly. In addition, with the correct choice of sampling arrangement and magnifica- Image-quality tion it also can significantly reduce the tunable filter tedious sampling requirements associ- ated with single-point collection meth- Configurable image Data analysis ods. For example, if the size scale (mag- formation optics for software nification) of the imaging experiment is variable field of view (FOV) set such that individual pixels represent relatively pure chemical components analysis methods can be used that sim- NIR NIR illumination illumination ply classify the chemical identity of each source source element. The resulting classification images provide high-contrast pictures of chemical distributions in the sample. Qualitative and quantitative information often can be derived through pixel- Sample counting or by analysis of the statistical Adjustable sample stage distributions of the classification results. While this approach is quick and simple to implement, chemical imaging Figure 2. Schematic diagram of an NIR chemical imaging instrument (diffuse reflectance mode). data obviously also are amenable to the

April 2004 19(4) Spectroscopy 29 Molecular Spectroscopy Workbench

the high-end of the price range, these much the same way as traditional FT-IR the majority of samples can be analyzed detectors are used for sensitive low-light mapping systems, obviating the need for noninvasively in diffuse-reflection with level applications in science and astron- a moving stage. NIR and Raman imag- little or no preparation and as a result, it omy; at the other end, they are used as a ing instruments have been constructed has been employed in numerous phar- camera embedded in a cell phone. The using solid-state tunable filter technolo- maceutical process applications. NIR-CI long-wavelength analogs of these detec- gies, which offer several distinct advan- enjoys these same advantages. While the tors are IR focal-plane array detectors tages for industrial applications, includ- focus of this article is to illustrate how that originally were developed for mili- ing mechanical simplicity and flexibility NIR-CI fits into the pharmaceutical PAT tary applications such as missile detec- for industrial applications. initiative, the instrumentation used for tion, targeting, and night-vision devices. NIR imaging also must fit. It should be It is only within the last decade or so NIR Imaging Instrumentation flexible, robust and amenable to the that they have been used by the general NIR spectroscopy has been shown to be manufacturing environment. IR spectroscopy community (15). an excellent tool applied to the solution Figure 2 shows a generalized Originally, only small format arrays of a wide range of pharmaceutical ap- schematic of a NIR imaging instrument (64 × 64 pixels) were available and these plications (2–4). It provides high-infor- using a tunable filter for wavelength dis- arrays were constructed from material mation content along with ease and crimination. The simple optical design such as indium antimonide (InSb) or flexibility in sampling. Compared with and compact size allows these instru- mercury–cadmium–telluride (MCT). many other spectroscopic approaches ments to be deployed in a wide range of They were prone to mechanical failure, required cryogenic cooling, and were (a) (b) quite expensive (>$10/pixel). More re- 0 – cently, as the technology has begun to 0.06 – shift from military applications to 2 – 0.04 – higher volume commercial uses, more economical, large format (320 × 256 0.02 – pixels) focal-plane arrays made from 4 – 0 –

InSb, MCT, or indium–gallium–ar- Distance (mm) 0.02 – senide (InGaAs) have entered the mar- 6 – 0.04 – ket (<$1/pixel). Many of these cameras Second derivative data 0.06 – operate uncooled or incorporate solid- 8 – 0.08 –| | | | | | | state thermoelectric cooling, exhibiting 1200 1400 1600 1800 2000 2200 2400 much improved operability and dura- | | | | | | Wavelength (nm) 0 2 4 6 8 10 bility. More recently, the IR camera Distance (mm) market has seen the emergence of the (c) (d) uncooled microbolometer array using 0.04 – 0.06 – low-cost CMOS technologies (16). 0.04 – These arrays promise to set whole new 0.02 – 0.02 – price performance levels for infrared 0 – 0 – focal plane arrays. 0.02 – -0.02 – Wavelength selection. As described ear- -0.04 – lier, the chemical imaging experiment is 0.04 – -0.06 – an exercise in collecting data from a Second derivative data 0.06 – Second derivative data sample along three dimensions: two -0.08 – spatial and one spectral. While the use 0.08 –| | | | | | | -0.1 –| | | | | | | 1200 1400 1600 1800 2000 2200 2400 1200 1400 1600 1800 2000 2200 2400 of an infrared focal-plane array pro- Wavelength (nm) Wavelength (nm) vides the two spatial dimensions, several approaches for coupling it to a wavelength selection device have been described in the literature (7, 15, 17) and, Figure 3. Visualizing the tablet composition of an over-the-counter pain medication. Shown in some cases, subsequently imple- are (a) an RGB image, where the red channel is a single-channel image at 2030 nm mented by instrument manufacturers. representing acetaminophen, the green channel is a single-channel image at 1660 nm repreenting aspirin, and the blue channel is a single channel image at 2250 nm representing Each technology has its own benefits caffeine; (b) A single-pixel microspectrum from a 40 40 µm spot from the red region, and limitations, but it is beyond the overlaid with a pure bulk acetaminophen spectrum; (c) a single-pixel microspectrum from a scope of this article to explore these in 40 40 µm area from the green region, overlaid with a pure bulk aspirin spectrum; and (d) a detail. Mid-IR and some NIR imaging single-pixel microspectrum from a 40 40 µm area of the blue region, overlaid with a pure instruments utilize the Fourier-trans- bulk caffeine spectrum. form scheme and as a result, function in

30 Spectroscopy 19(4) April 2004 www.spectroscopyonline.com situations. They have no moving parts finished process applications might only like most tablets, this sample is not and, with the exception of power, re- require collection over a narrow spectral blended homogeneously even when vi- quire no external utilities. Thus, instru- range or even just a few analytically rel- sualized at fairly modest magnifications ments also can be mounted in side- evant wavelengths. The ability of the but is composed of a matrix of localized looking or inverted orientations. tunable filter to access these wavelengths domains, or particles, of each of the Laboratory instruments normally are randomly can be used to reduce the component materials. mounted in a downward looking orien- time needed to collect the data dramati- Casual inspection of the image readily tation, on a stand fitted with the illumi- cally. Well-defined methods can be opti- indicates that the caffeine component nation source and a sampling stage. mized and bundled such that collection has the smallest mean particle size and A great benefit of these instruments is and analysis is integrated and accom- has the lowest relative abundance of the their “staring” configuration coupled plished in real time with little or no op- three APIs (fewer red domains). The with a variable field of view. Working in erator intervention. acetaminophen particles also are quite the NIR permits the use of refractive distinct and are somewhat larger than optics and the simple optical design al- Application Examples those of caffeine while the aspirin ap- lows the user to adjust the magnifica- and Possibilities pears to form the continuous matrix in tion of the instrument simply by ex- Component distribution visualization. Fig- which the relatively large domains of the changing the image formation lens. A ure 3 depicts the results of imaging other two components sit. The high-con- standard laboratory system can be con- analysis of an over-the-counter pain trast image also can be used to provide figured for microscopic applications medication. The tablet was imaged with more quantitative information quickly. (<10 µm/pixel) or macroscopic applica- the Sapphire (Spectral Dimensions, By simply measuring the area of coverage tions (~500 µm/pixel). The result is a Inc., Olney, MD) NIR-CI system in dif- of each of the domains a quick estima- chemical image data set comprising tens fuse reflectance with a single-pixel mag- tion of the composition of this tablet can of thousands of spectra of a single phar- nification of 40 × 40 µm. The chosen be determined without the need for first maceutical granule or an entire blister spectral range for this particular data deriving a calibration curve. pack collected rapidly from the same in- set was 1200–2400 nm, with 10-nm Clearly, one also could derive a stan- THE FDA-SUPPORTED PAT INITIATIVE APPEARS TO HAVE GATHERED SIGNIFICANT PACE AND MOMENTUM DURING THE PAST YEAR AND WILL HAVE A MAJOR IMPACT UPON THEWAY PHARMACEUTICAL MANUFACTURING IS CONDUCTED IN THE FUTURE. strument. Instruments which image data spacing. The total time to collect dard NIR calibration curve from a series even larger areas can be purpose-built all 81,920 spectra was approximately 5 of mixture spectra and apply conven- for process, high throughput, or other min. The data were transformed using a tional multivariate methods such as PLS specialized applications. The optical second-derivative calculation to high- to each pixel individually. Although this configuration supports relatively large light the chemical differences and to approach works universally and typi- depths-of-field so curved or uneven minimize contributions from sample cally provides an improved result, the sample surfaces do not pose significant topology and scattering. Initial interro- binary approach, when applicable, is problems, making it possibly the most gation of the hypercube suggested that quicker, simpler and only requires ac- rugged and robust chemical imaging three distinct spectral types were pres- cess to a single tablet. Further, by using technique available. ent, each having uniquely characteristic the binary chemical images for each of The tunable-filter technology also has absorption bands. the three APIs separately, automated other distinct PAT advantages. As stated The intensity images at 2030, 2250, software tools can be applied to derive above, these devices have no moving and 1660 nm each were assigned a color quantitative data based on particle sta- parts, and their small size allows them (red, blue, and green, respectively) and tistics. These tools can assess the size to be combined with a focal-plane array overlaid to form the RGB image shown and shape of individual particles as well into a unified wavelength-selectable in Figure 3a. Individual pixel spectra as determine average values and compo- chemical imaging engine. Discrete from the contrasting domains were nent distribution information for the wavelengths can be selected rapidly, compared with reference bulk spectra sample as a whole. through software control, and a full- (Figures 3b–d) and revealed that this While much of the emphasis in the spectrum/hypercube comprising ap- product primarily is composed of three past for determining pharmaceutical proximately 80,000 spectra collected in active ingredients, acetaminophen (red), quality has relied on determining purity less than 5 min. For most research and acetylsalicylic acid (green), and caffeine and potency it now is clear that the problem analysis experiments it is use- (blue). The composite image shows the component distribution and particle ful to collect data over the entire spec- distribution of each of the components sizes of both the active ingredient and tral range of the instrument. However, in the finished product. It shows that, excipients can impact a product’s man-

April 2004 19(4) Spectroscopy 31 Molecular Spectroscopy Workbench

ufacturability, stability, and dissolution characteristics. NIR-CI is a very useful (a) (b) tool for identifying the root causes of 0 – such defects and failures. The ability to visualize and quantify uniformity, com- 2 – ponent distributions, and particle sizes )

and shapes within blends or finished 4 – R solid dosage forms can provide insight Log(1/

into the physical forces that influence Distance (mm) 6 – the manufacturing process. Imaging analysis incorporated into the prefor- 8 – mulation and scale-up phases can be 10 – used to positively ascertain the influ- | | | | | | 1100 1200 1300 1400 1500 1600 1700 ence of each of the unit operations such 0 2 4 6 8 10 Wavelength (nm) as granulating, milling, drying, and Distance (mm) blending allowing optimization of the (c) (d) process and preventing failures in the first place. 0 – Contaminant–trace analysis. Figure 4 represents the NIR-CI analysis of a 2 – tablet that contains a single API com- ) ponent in a mixture of excipients. In 4 – R

this study a library of pure-component Log(1/ spectral data was used to construct a 6 – PLS model to derive the contribution Distance (mm) and distribution of the individual ma- 8 – terials. When the model is applied to a 10 – | | | | | | sample hypercube, each spectrum 0 2 4 6 8 10 1100 1200 1300 1400 1500 1600 1700 Wavelength (nm) (pixel) is assigned a score denoting the Distance (mm) relative abundance of the modeled component at that particular location. Figure 4. Trace contaminant analysis of a furosemide (API) sample. Shown are (a) a PLS score The PLS score image for furosemide image highlighting a furosemide-rich area; (b) spectra of the pure API (red) and the (the API) is shown in Figure 4a and degradation product (blue); (c) a single-channel image at 1444 nm highlighting the impurity indicates that the distribution is much rich areas — the impurity concentration derived from sample statistics is ~ 0.61%; and (d) a more homogeneous than in the previ- residual microspectrum (red) observed at the center of one of the bright spots after ous example. However, furosemide has subtracting the variance due to the predominant chemical component (an excipient) from the been shown to break down under cer- entire data set — compare this spectrum with the impurity spectrum in (b). tain conditions, possibly resulting in the presence of a contaminant in the finished product. The NIR spectra of area (Figure 4c). Single-pixel residual spectral features simply are lost in the the API and the degradation product spectra from these regions closely re- average of the stronger signals obtained are overlaid in Figure 4b. The later ex- semble the known spectrum of the from the rest of the sample. Micro- hibits a prominent spectral feature at degradation product (Figure 4d) and scopic approaches can provide highly 1444 nm, allowing it to be distin- verify its presence in the sample tablet. localized spectra, effectively increasing guished readily from both the API and The overall abundance of the impurity the relative concentration (and thus, excipient materials. in the sample was again calculated the detectivity) of a scarce component Because impurities are expected to through pixel-counting statistics and es- in the sampled area. However, tradi- occur at very low concentrations, the timated to be approximately 0.61% of tional microspectroscopy requires the spectral contribution from the drug total tablet volume. selection of the correct location for de- material was enhanced in the image This analysis pinpoints another ad- tection. Therefore, one either must have through a scaled subtraction of the vantage of chemical imaging over sin- prior knowledge of the location of the spectrum of the bulk (excipient) mate- gle-point spectroscopic analysis tech- impurity, or it must be found by time- rial from each pixel in the original hy- niques. Low-concentration or weakly consuming mapping techniques. NIR- percube. The single-channel image at absorbing species often are difficult or CI collects spatially organized mi- 1444 nm of the residual data clearly impossible to detect in the mean spec- crospectra from large area of the shows several small areas of increased trum obtained through bulk, macro- sample in a single experiment. intensity distributed across the sample scale spectroscopy. The distinguishing The full area of a typical 1-cm di-

32 Spectroscopy 19(4) April 2004 www.spectroscopyonline.com Molecular Spectroscopy Workbench ameter tablet sample can be interro- distinctly different spectra (Figure 5b). information provided by NIR-CI is in- gated with a spatial resolution of about Quantitative information about the valuable in both the development and 40 × 40 µm in only a few minutes, pro- dosage form was obtained from the manufacture of complex delivery sys- viding both enhanced sensitivity, and image simply by setting the appropri- tems such as this product. Note the rela- location information. Even if a rogue ate intensity level so as to define each tively uneven nature of the coating ob- material is detected but is unidentifi- of the observed spheres as a discrete served in the image of the bright sphere able by its NIR spectrum alone, the lo- particle (Figure 5c). Automated image in Figure 5d. It ranges in thickness from cation information of the imaging ex- analysis of the result indicated that approximately 150 to 250 µm. Imaging periment greatly assists in the rapid there are twice as many bright — 91 analysis during the development and analysis of the suspect region by other — as dark — 45 — spheres in this par- scale-up of a process which produces analytical methods. In other experi- ticular field of view, and that the the coated spheres would provide a clear ments, we also have used this approach bright spheres are, on average, approx- picture of this component and allow the with some success to determine the ex- imately 5% larger in diameter. critical control parameters to be quickly istence and localization of low levels of The mechanism of the form was elu- identified, thus improving quality and different polymorphic forms within cidated through the further analysis of reducing the risk of costly performance finished products.The NIR-CI analysis the individual sphere types. One of each failures. During manufacturing, chemi- of an extended-release dosage form is type of sphere was cut in half and the cal imaging could be applied to monitor shown in Figure 5. This product is a cut faces were analyzed at higher magni- the uniformity of coating thickness, capsule filled with small microspheres fication. The resulting image (Figure mean diameter, and relative composi- containing the therapeutic agent and 5d) reveals that the dark sphere is rela- tion of mixtures of different types of extended release mechanism. A sample tively homogeneous while the bright microspheres enabling the desired com- of the filling was removed from a cap- sphere is made up of a coating sur- position to be maintained. sule and imaged with the Sapphire rounding a core composed of the same High-throughput applications. Figure 6 NIR-CI system. The single-channel material found in the dark spheres. This demonstrates how NIR-CI can be con- image at 2130 nm (Figure 5a) indicates coating presumably comprises the ex- figured as a high-throughput technol- that there are two types of spheres tended release mechanism. ogy for use in the pharmaceutical man- present in the sample, each producing It is readily apparent that the spatial ufacturing process. In these

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applications, the highly flexible field of the number of objects that can be ad- also, in the case of double-blind trials, view and robust imaging capability of dressed simultaneously in this manner the dispensing physician. For this to be the technique are used to great value to is only limited by magnification and feasible, the physical size and shape of spatially analyze a larger array of sam- the number of pixels on the infrared all types of dosage forms must be indis- ples, simultaneously. In this example a array. For instance, the data in Figure 5 tinguishable. The ability to rapidly ver- sealed blister pack containing 10 visu- also can be considered in the same ify the efficacy of this complex packag- ally identical white tablets, approxi- manner. In this case 136 objects were ing process after the product is sealed mately 7 × 11 cm in size, was analyzed. examined simultaneously. offers significant benefit. Before the experiment one of the tablets There are numerous applications for Errors can void a clinical trial, im- was removed and replaced with an iden- such a system in which it simply re- posing significant costs in both imme- tical form containing a different API. places single-point or multiplexed NIR diate resources and lost time to market Figure 6a is a visible image of the adul- spectrometers, providing significant ad- for a new drug. In many cases this terated package. vantages in sample throughput and array-based approach can be opti- The NIR spectral image of the com- handling. Furthermore, these advan- mized so that only a few carefully se- plete sample was collected without dis- tages can operate over a range of size lected wavelengths are needed for the turbing the samples or the packaging. scales and sample shapes that are diffi- identification, yielding an inspection The PCA score image of the arrange- cult or impossible for current single- time on the order of seconds, which is ment in Figure 6b clearly identifies the point instrumentation to address. One critical if 100% inspection is the goal. rogue tablet containing the different such example is the validation of the In addition, the large, flexible field of active form. Although the result of this filling of clinical trial blister packs in view of an array-based approach en- measurement is an image, the data also which a series of variable dosage or ables a variety of package shapes and can be considered as simply a series of placebo dosage forms are handled and orientations to be analyzed with little NIR spectra taken in parallel. With this packaged in predefined geometric or no reconfiguration. thought in mind we can interpret the arrangements. Clearly, the intent of data as a quality control measurement such an exercise is to provide a prede- Final Thoughts performed on all 10 tablets simultane- fined dosage regimen to individuals, in The FDA-supported PAT initiative ap- ously. Furthermore, it is obvious that a manner that is blind to the patient and pears to have gathered significant pace

Circle 21 Circle 22 34 Spectroscopy 19(4) April 2004 www.spectroscopyonline.com (a) (b)

0 0.4 – 2

4 0.2 –

Distance (mm) 6 0 – First derivative data 8

10 -0.2 – | | | | | | | 1200 1400 1600 1800 2000 2200 2400 0 2 4 6 8 10 12 Wavelength (nm) Distance (mm)

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Distance (mm) 6 0.6 - Distance (mm) 8 0.8 - 0 0.5 1 1.5 10 | | | | | | | Distance (mm) 0 2 4 6 8 10 12 Distance (mm)

Figure 5. Whole microbeads from an extended-release dosage at low magnification showing two distinct types. Shown are (a) a single-channel image at 2130 nm; (b) single-pixel microspectra of the two bead types; (c) an image obtained after performing particle-contour statistics; and (d) high-magnification chemical images showing spatial differences in the composition of the two types of beads identified in (a) — the left and right hand beads correspond to the dark and bright beads from (a).

(a) (b)

0– ) 4

10 2– ✕ m

4–

6– Distance (

8 024681012 Distance (m ✕ 104)

Figure 6. An adulterated pharmaceutical blister pack containing a single rogue tablet. Shown are (a) a visible image and (b) an NIR PCA score image.

Circle 23 April 2004 19(4) Spectroscopy 35 Molecular Spectroscopy Workbench and momentum during the past year References 17 (2002). or so, and undoubtedly will have a 1. http://www.fda.gov/cder/OPS/PAT.htm 10. H. Mark, Anal Chem. Acta. 223, 75 major impact upon the way pharma- 2. K.A. Bakeev, Spectroscopy 18(11), 32 (1989). ceutical manufacturing is conducted (2003). 11. P. Geladi and H. Grahn, Multivariate in the future. The basic message is not 3. C.T. Rhodes and K. Morissau, in Encyclo- Image Analysis (John Wiley & Sons, just the implementation of more in- pedia Pharmaceutical Technology, 2nd United Kingdom, 1996). process measurements to shorten ex- ed., J. Swarbrick and J.C. Boylan, Eds. 12. http://www.spectraldimensions.com/ isting quality assurance–quality con- (Marcel Dekker, New York, 2002) pp. ps_isys.php. trol times but to embrace the concept 2689–2700. 13. R. Barer, A.R.H. Cole, and H.W. Thomp- of process understanding, ultimately 4. Pharmaceutical and Medical Applications son, Nature 163, 198 (1949). leading to process optimization. In of Near-Infrared Spectroscopy, E.W. 14. M.A. Harthcock and S.C. Atkin, Appl. order to accomplish this, the industry Ciurczak and J.K. Drennen III, Eds. (Mar- Spectrosc. 42, 3 (1988). will need to look toward new tech- cel Dekker, New York, 2002). 15. P.J. Treado, I.W. Levin, and E.N. Lewis, nologies that can provide true insight 5. S.V. Hammond, European Pharmaceuti- App. Spectrosc. 46, 553 (1992). into the component relationships and cal Review 3(4), 47 (1988). 16. D.S. Tezcan, S. Eminoglu, and T. Akin, physical forces that drive and deter- 6. F.C. Clarke, R.D. Jee, A.C. Moffat, and S.V. IEEE Trans. Electron. Devices 50(2), 494 mine the quality and performance of Hammond, J. Pharm. Pharmacol. 52, 66 (2003). pharmaceutical products. NIR-CI is (2000). 17. E.N. Lewis, P.J. Treado, R.C. Reeder, G.M. such a tool. 7. E.N. Lewis, J.E. Carroll, and F.C. Clarke, Story, A.E. Dowrey, C. Marcott, and I.W. NIR News 12(3) 16 (2001). Levin, Anal. Chem. 67, 3377 (1995). ■ Acknowledgments 8. R.C. Lyon, E.H. Jefferson, C.D. Ellison, L.F. The authors would like to acknowl- Buhse, J.A. Spencer, M.M. Nasr, and A.S. E. Neil Lewis is chief executive officer of edge the support of Dr. Robbe Lyon Hussain, Amer. Pharma. Rev. 6(3), 62 Spectral Dimensions, Inc. (Olney, MD). and Dr. Ajaz Hussain of the USFDA (2003). Joe Schoppelrei and Eunah Lee for providing the contaminant sample 9. R.C. Lyon, D.S. Lester, E.N. Lewis, E. are applications scientists for Spectral and pure component materials re- Lee, L.X. Yu, E.H. Jefferson, A.S. Hus- Dimensions. Please address correspondence ported in this work. sain, AAPS PharmSciTech. 3(3), article to: [email protected].

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