Use of Near Infrared Spectroscopy in Tablet Evaluation.

Prepared by- Niket Patel

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Outline

Introduction Near infrared spectroscopy(NIRS) and basic NIR region NIRS design set up and instrumentation Theoretical basis of NIR spectra Use of chemomatrics for analysis of the NIR spectra Tablet evaluation using NIRS Emphasis on tablet hardness and content uniformity Limitations of NIRS in tablet evaluation Current regulatory status of NIRS in tablet evaluation Summary

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NIR spectroscopy: • Spectroscopy is a scientific discipline studying interactions of light with matter. • Light can be of different wavelengths which are represented by the electromagnetic spectrum applied.

Figure- Electromagnetic spectrum

• The far-infrared region (400–10 cm−1), • The mid-infrared region (4000–400 cm−1), and • The near-infrared region (13,000–4000cm−1)(in terms of wave numbers.) The NIR region mainly used in the analysis of pharmaceutical products is

1100 nm to 2500 nm.(interaction of light of this wavelength to matter.)

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NIR region:

Figure: Detailed NIR region

• Absorption of light in the IR region causes molecules to vibrate and rotate.(due to interaction of light to those bonds).• Absorption of light in the matter is usually not uniform and depends on molecular structure.(number and type of bonds present in the molecule.)• At certain intervals the absorption is more intense, which is represented in the form of absorption bands.

• The NIR region of the spectrum mainly contains overtones and combination bands that are primarily attributed to hydrogen vibrations (CH, OH, NH).

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Continue…• These overtones and combination bands are secondary vibrations

and much weaker than the fundamental vibrations, so molar absorptivities are less.

• NIR spectra have only a few significant peaks, but they are exceptionally information-rich due to the number of overlapping absorption bands.

• Interpretation of NIR spectra is usually combined with mathematical and statistical methods such as chemometric methods in order to extract the necessary information.

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Design set up for NIR spectroscopy:

Figure: NIR spectrometer- basic design set up and measurement modes

Depending upon the arrangement.• Transmission: detector placed behind the sample.• Reflectance: detector placed on the same side of sample.

• Light source: a tungsten halogen lamp- small and rugged) electrically heated to 1500–2200K

• Monochromator: Used to spilt the radiation.Mainly used: Diffraction grating

• Detector: Used to record the signal after wavelength separation. Photon detectors are the most widely used in NIRS.

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NIRS Instrumentation:

Figure - Arrangement of sample in NIR instrument.

• Sample can be active ingredient or tablet itself.

• NIR instruments have the basic design as shown.

• The sample may then be placed in the sample holder, which may hold one or more of a specific type of sample.

• The sample is positioned, the lid closed, and the scan taken.

• For multiple scans of the same sample or scans from the different positions are taken.

• Detectors converts the scattered light into spectra which is further used for analysis.

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NIR spectroscopy and pharmaceutical ingredients• Pharmaceutical drugs and excipients gives different NIR spectra.

• The record of NIR region of the electromagnetic spectrum involves the response of the molecular bonds O–H, C–H, C–O and N–H.

• These bonds are subject to vibrational energy changes when irradiated by NIR frequencies.

•The energy absorption of organic molecules in NIR region occurs when molecules vibrate or is translated into an absorption spectrum within the NIR spectrometer.

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NIR spectroscopy and pharmaceutical ingredients

The near infrared spectral library "NICODOM NIR Pharmaceuticals“ contains 696 NIR spectra (4.200- 11.000 cm-1) of active substance and excipients used in pharmaceutical industry. The source of the samples were local pharmaceutical companies.

How do we process tablets (mixture of actives and excipients)???

Different drugs and excipients give different absorption values at different wavelengths and typical NIR spectra for individual can be obtained.

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Typical NIR spectra of tablet:

Single-tablet reflectance spectra with repeated positioning using an automatic tablet transport system. The 3 irregular spectra are the result of tablet misalignment on the transport conveyor belts

Single-tablet transmission spectra with repeated positioning using an automatic tablet transport system. The 3 irregular spectra are the result of tablet misalignment on the transport conveyor belts.

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Change in NIR spectra related to evaluation of tablet parameters

As shown in the previous slide, typical tablet NIR spectra gives the reflectance or transmission values at different wavelength.

Change in the tablet parameters such as content of the active, tablet harness, dissolution time changes the typical NIR spectra and different reflectance or transmission values are obtained.

Change in the NIR spectra contains the information about the tablet parameters and use for the quantitative analysis of the tablet parameter.

Quantitative analysis of the NIR spectra to relate it with tablet evaluation parameters is a multi-step process involving mathematics and statistics.

For better understanding the whole process we will compare it with quantification of active content using HPLC.

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Quantitative analysis of NIR spectra:

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Mathematical pretreatment: Variable physical sample properties or instrumental effects cause

interference in NIR spectrum.

Interfering spectral parameters involves light scattering, path length variations, optic effects and random detector noise.

Some mathematical corrections, called as data pretreatments, prior to multivariate modeling are carried out in order to reduce, eliminate or standardize impact of interference parameters on the spectra.

Selected mathematical data pretreatments can significantly improve the robustness of a calibration model.

Mathematical treatments used to compensate for scatter-induced baseline offsets include multiplicative scatter correction (MSC) and standard normal variate (SNV).

MSC and SNV are algorithm helps in normalizing baseline on NIR spectra.

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Mathematical pretreatment:

Effect of SNV or MSC pretreatment on Single-tablet reflectance spectra

Effect of SNV or MSC pretreatment on Single-tablet transmission spectra

Second derivative spectra contains all the spectral information together so extraction is required. 14

Extraction of distribution maps: Second derivative spectra obtained after data

pretreatment should be extracted for the desired components.

The information from the mathematical pretreatment is in the form of distribution maps.

Extraction of these maps is carries out for localization of chemical compounds in the distribution maps as shown in the figure. Each color of the image

represents different chemical compound.

Extraction has to be as accurate as possible to avoid pixel misclassification.

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Extraction of distribution maps: Univariate analysis Each chemical entity present in a tablet scatter the light at specific

wavelengths depending on its chemical bonds. Selecting the image at those wavelength positions localizes the

specific compounds If a constituent is unknown (contaminated product for example) or

at such low concentration, univariate analysis fails to extract sufficiently reliable distribution maps.

Multivariate analysis To overcome the limitation of univariate analysis, multivariate

analysis of pharmaceutical product is carried out to get distribution maps. Multivariate analysis takes into account all the spectral information contained in the data cube

Principal component analysis (PCA) for reduction of variables Particle least squares (PLS) for reduction of variables

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Calibration After extraction of the distribution maps, different absorption values

at different wavelength for a chemical entity can be obtained. For tablet evaluation parameter, these absorbance values are

related to the value of interested parameter.

For content uniformity- Tablets with different known amount of actives are prepared by

keeping all other excipients constant and NIR spectra is taken. Variation in the absorbance values can be related to the amount of active.

For tablet hardness- Tablets with different hardness are prepared by keeping all other

parameters constant and NIR spectra is taken. Variation in the absorbance values can be related to tablet hardness.

Multiple spectra are taken for the same amount and tablet hardness to ensure the robustness of the results.

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Calibration for quantitative analysis: Calibration models are developed to determine the

relationship between calibrated set of spectra and the constituent value of interest (amount of active/ tablet hardness)for those samples.

Calibration involves taking spectra from many samples varying over the measurement range from lower to higher value and measuring the desired parameters.

Samples selected for calibration must contain all of the variables affecting the chemical and physical properties of the samples to be analyzed. To characterize each source of variation, 15 to 20 samples to be run for each variable is recommended

Application of a mathematical treatment as discussed above, prepares the raw spectral data for use in a regression and subsequent development of a calibration equation

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Calibration and validation of the results:

Figure: Calibration and validation set of amount of the active present in the tablet.

NIR spectroscopy is secondary method for analysis; requires primary results to compare.

Results for the amount of the active obtained with HPLC method is compared with results obtained using NIR spectroscopy.

Calibration and validation of the obtained results are carried out to obtain robust results.

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Validation of the calibrated model:

The calibrated model relating spectrum to quantitative measures of tablet properties should be validated.

The principal elements of validation ensuring linearity, accuracy, selectivity, and reproducibility of a quantitative calibrated model are required.

The validation process determines the amount of error due to variation among the values in analytical properties.

NIRS instrumentation mainly include software packages that allow the operator to predict analytical results on the stored data files, thus allowing for validation of the established calibration equation and testing for errors in the developed calibration.

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In summary,

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Evaluation of tablet parameters:

After manufacturing of tablets, tablets have to be characterized or described by various parameters in order to assure the integrity of the manufacturing process and to meet up the regulatory requirements.

Evaluation of tablets assures manufacture for the variation in tablets from one production lot to another.

Official standards for the evaluation of tablets are given by the U.S. Pharmacopeia (USP) and other compendia and include uniformity of dosage units (weight variation, content uniformity) and disintegration testing.

Unofficial tests include those for mechanical strength (hardness or crushing strength) and resistance to abrasion (friability).

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USP official methods for tablet evaluation: Content Uniformity:

Content uniformity testing ensures the concentration of API from tablet to tablet across an entire batch.

It decides physiological availability of active so, the content uniformity test has been included in the monographs of all coated and uncoated tablets.

Tablets have to meet the criteria for acceptance given in the USP.

Currently used methods for determining concentration of active involves use of UV spectroscopy and HPLC.

Dissolution testing:

Tablet dissolution is a standardized method for measuring the rate of drug release from a tablet.

It decides the therapeutic effectiveness of the tablet so, dissolution testing is the official test for tablet evaluation.

Tablets have to meet the criteria for acceptance given in the USP.

Currently used method involves use of various USP dissolution apparatus (7 types) and assay of the sample using UV spectroscopy or HPLC.

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Unofficial methods for tablet evaluation:

Tablet hardness Tablet hardness shows

mechanical strength of tablet to withstand the shock of handling during various phases of shelf life.

It is also known as ‘tablet crushing strength’.

Tablet hardness should be enough to withstand the mechanical shocks.

Tablet strength also affects the other more important parameters of tablet such as disintegration and dissolution.

Current methods for evaluation of tablet involve use of various hardness testes such as the Erweka tester, the Stong-Kobb tester and the Pfizer tester.

Friability Friability is the tendency of a

tablet to crumble, chip or break.

In simple terms, it inversely proportion to tablet hardness.

Friable tablets can be caused by low moisture content, insufficient binder, tablet configuration (e.g. sharp versus beveled edges). 

Current method It is measured by tablet weight loss after rotation on a friabilator (i.e. 100 revolutions or 4 minutes at 25 RPM).

eg. Roche friabilator

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Limitation of the current methods: Conventional hardness testes involves operator error,

possibility of an incorrect zero and scale which does not accurately indicate the true load applied.

UV spectroscopy and HPLC. Laboratory methods for tablet assay and content uniformity are usually time-consuming because they require lengthy calibration runs, the mixing of buffers, and the procurement and disposal of volatile solvents.

Analyzing tablets for content uniformity may take hours and may not be available for batch release for many days.

A major disadvantage of current methods of tablet evaluation is that they are time-consuming and destructive in nature. Once a test is performed on a sample, the integrity of that sample is usually lost.

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NIR spectroscopy in tablet evaluation NIRS provides a rapid and non-destructive tool to determine

various evaluation parameters. NIRs helps in identification, assay and content uniformity and

also for physical and biopharmaceutical parameters, such as hardness, coating thickness and dissolution rate.

NIR spectroscopy provides fast and nondestructive measurements,

As we have seen variation in the vibration bands are the basis of the NIR spectra.

Change in the tablet evaluation parameters changes the NIR spectra also in the same manner due to some reasons.

We are going to see how tablet evaluation parameter changes NIR spectra and how it can be quantified.

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Content uniformity:

The content uniformity test is carried to ensure that every tablet contains the amount of drug substance intended with little variation among tablets within a batch.

Tablets are evaluated for the quantity of the active ingredient.↕

Chemical structure of the active remains same, only the quantity that active changes.

↕Number of the chemical bonds varies, change in the active’s

bonds vibration absorption↕

Basic NIR spectra remains same, only absorption values changes due to change in the amount of active ingredient.

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Evaluation of content uniformity using NIR spectroscopy:Comparison of NIR spectra of tablets with different amount of actives.

Second derivative spectra of the tablets with different amount of actives.

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Continue…

Calibration equation is derived and will be used to find the amount of active present in the unknown tablet.

Second derivative NIR spectra relates the absorption intensity at a particular wavelength to the amount of the drug present in the tablet.

Multiple NIR spectra is taken for calibration and validation of the results.

Tablets with known amount of active are evaluated with HPLC/UV for a reference results.

Various statistical treatments relate absorption intensity to the amount of active present in the tablet and gives a calibration equation.

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Tablet hardnes:

Change in NIR spectra

Change in tablet hardness

Compression pressure applied to tablets↓

Reduce the porosity of the tablet ↓

More compact mass formed↓

Do not allow NIR light to penetrate easily ↓

Decreased the scattered light↓

Change in the NIR spectra.

How tablet hardness is related to change in NIR spectra ?

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Effect of Compression pressure on tablet harness

As the tablet hardness increases, the roughness of the surface decreases with increasing compression pressure. change in the surfaces cause change in the NIR spectra mainly due to transmission.

SEM micrographs of the surface of the tablets with increasing compression pressure from figure (a) to figure (d).

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Effect of compression pressure on tablet hardness:

Since there is a larger air/solid boundary surface area in high porosity tablets manufactured with lower compression pressure, the intensity of scattered light is greater than that of transmitted light in the tablet. Conversely, since there is a larger solid/solid boundary surface area in tightly packed tablets, the intensity of scattered light is less than that of transmitted light.

Light diffusion models of the loosely and tightly packed tablets by diffused reflectance and transmittance methods.

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Evaluation of tablet hardness using NIRS:

Basic NIR spectrum of chlorpheniramine tablets using different hardness levels.

Second derivative of NIR spectrum of chlorpheniramine tablets using different hardness levels

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Continue…

NIR spectra of the unknown tablet is taken and absorbance value is related using the calibration equation.

At a particular wavelength, absorbance values are related to the tablet hardness values.

In a simple terms, for better results, several spectrums are taken at the same tablet hardness.

In real means, Second derivative NIR spectrum are further processed with multilinear regression and partial least squares(PLS) regression for extracting the information from the NIR specrum of all spectra runs and they may be correlated to tablet hardness and calibration equation is established

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Tablet Dissolution:• Tablet dissolution is the secondary parameter of the tablet .

• Change in the dissolution time of the tablets depends on the compression pressure applied for the manufacturing of the tablets.

• So, the reason for the change in NIR spectra remains the function of applied compression pressure.

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Continue…

Figure 1. Different compression pressure results in different absorbance values at a given wavelength. Again, raw data is converted to second derivative spectra and related to the tablet dissolution time data (reference method).Calibration equation is established for further tablet dissolution evaluation.(Figure 2)

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Advantages of NIRS over current methods:

The energy of NIR radiations is small enough to allow a non-destructive analysis of samples.

NIR spectroscopy enables the analysis of a wider variety of samples, including for instance strongly absorbing samples and opaque solid materials.

NIR spectroscopy requires little or no sample preparation without any pretreatment and it therefore enables easy and fast data collection.

NIR spectroscopy do not require sample removal from the tablet batch so NIR analyses do not require the use and ultimate disposal of organic solvents, thereby reducing environmental waste.

Materials, such as glass or translucid plastic, do not interact with NIR light. NIR light can be directly sent through the packing material, if samples are packed in such materials in order to analyze the samples. So NIR spectroscopy can analyze tablets through the plastic blister, without removing it.

Samples may be retained for further analysis by NIR or other methods, allowing a direct correlation between tests. Economic benefits are obvious for manufacturers, who may increase profits per batch because of the need for fewer retained samples.

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Limitations of NIR spectroscopy in tablet evaluation: The accuracy of the NIR method cannot be better than the

reference method (HPLC/UV) from which it was validated. The initial calibration process for a substance or a product

should be quite detailed. A calibration equation is needed for each constituent in the sample for the better result.

Physical attributes of the tablets can affect the calibration process. For example, scored tablets and those of during geometries may produce more variability in NIR spectra than flat, unscored tablets.

Homogeneity of the sample affects the NIR spectra and mixed calibration models composed of flat and concave tablets gave variable hardness prediction results, supporting the assertion that calibration models should contain samples of homogeneous composition.

Another issue is that of transferability of the calibration model among instruments. This has been a significant obstacle to more widespread use of NIR methods.

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Calibration transfer issue: Transferability is especially important to multisite facilities, because

it is needed to avoid time consuming recalibration procedures. Development of the calibration method for quantitative analysis of

analytes is time consuming and expensive due to the reference analyses.

Therefore, developing a new calibration for each new spectrometer is very time consuming and uneconomical. Therefore, the calibration transfer aim is developed to apply a unique calibration model on several spectrometers with equivalent prediction errors.

In practice, the model is developed on a first spectrometer called “master” instrument and is used on several other spectrometers. However, even the instruments produced by one manufacturer do not produce exactly the same spectra.

For successful transfer of calibration model to device to device, the time adjustments are necessary

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Integration of tablet evaluation parameters ?? In practice, when NIR spectra is analyzed for content uniformity, all

other parameters such as tablet harness should be kept constant.When tablet is scaned to obtain NIR specrta, change in the

absorbance values can be a function of amount of active, tablet hardness or both of them.

In these cases, the accurate results are very difficult to achieve.

Dissolution testing:Evaluation of dissolution using NIR spectroscopy, mainly relates the

change in spectra, due to change in compression pressure, to reference dissolution data.

It’s a indirect measurement of dissolution time compare to current method.

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Current regulatory status of NIRS: In the highly regulated pharmaceutical world, an analytical

method is only valuable for routine implementation if it is approved by regulatory authorities.

The general legal requirements for instrumentation qualification procedures, namely design qualification (DQ), installation qualification (IQ), operational qualification (OQ), and performance qualification (PQ), are described in the cGMP guideline title 21 CFR part 211.

 The American Society for Testing and Materials (ASTM) recently published an official document providing a guide to spectroscopists for the multivariate calibration of infrared spectrometers. This document is the first official standard for the application of chemometric multivariate analysis to near-infrared and infrared instruments.

Not approved for tablet evaluation in any country all around the world

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NIR spectroscopy as analytical tool in view of the USFDA -Initiative on PAT

The production of pharmaceutical dosage forms is usually a multistage operation.

Quality assurance, including decisions concerning the satisfactory completion of each unit operation, is actually based on off-line testing to document quality of a small, nominally random product sample.

This approach is often very time consuming and significantly lengthens the manufacturing cycle, since it requires the process to be stopped during sample removal, data generation and documentation.

The Process Analytical Technology (PAT) initiative, driven by the United States Food and Drug Administration (USFDA) and major pharmaceutical companies, might be a solution for current situation

NIR spectroscopy and imaging may be one of the major PAT tools, since these techniques are well-suited for at-line, in-line and on-line measurements.

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Summary: NIR spectroscopy is a rapid and nondestructive means of tablet

evaluation, well researched and well accepted method by academia.

Involvement of mathematics and statistics makes it a complex method to develop a calibration model.

NIR spectroscopy is an important part of a FDA’s PAT initiative, which makes the companies to look into this field.

Expensive technology, very high upfront cost and need for the professionals to run the evaluation hinders the small companies to accept NIR spectroscopy.

In future, change in the regulatory status of tablet evaluation such as addition of NIR spectroscopy in USP may change the scenario of current pharmaceutical practices.

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Thank you!!

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