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IR Spectroscopic
6
Analytical Tools
in the Fight Against
Counterfeit Medicines
CONTENTS
6.1 Introduction ............................................................................................... 132
6.2 Fundamentals of Infrared Spectroscopy .................................................... 135
6.2.1 Near- Infrared Spectroscopy...........................................................135
6.2.2 Mid- Infrared Spectroscopy ............................................................137
6.2.3 Comparison of NIR and ATR- FTIR Spectroscopy ........................139
6.3 Chemometric Approaches used in Combination with IR Spectroscopy .......140
6.3.1 Data Pre- Processing ......................................................................142
6.3.2 Unsupervised Methods ..................................................................142
6.3.3 Supervised Methods ......................................................................143
6.3.4 Regression Methods ......................................................................145
Sangeeta Tanna
1
Leicester School of Pharmacy, De Montfort University,
Leicester, United Kingdom
2
Faculty of Health and Life Sciences, De Montfort
University, Leicester, United Kingdom
6.2.2.1 Attenuated Total Reectance Fourier Transform
Infrared Spectroscopy .....................................................138
6.3.2.1 Principal Component Analysis ........................................142
6.3.3.1 Linear Discriminant Analysis .........................................143
6.3.3.2 Soft Independent Modelling of Class Analogies ............143
6.3.3.3 Data Driven- Soft Independent Modelling of Class
Analogies ........................................................................144
6.3.3.4 Partial Least Squares- Discriminant Analysis ..................144
6.3.3.5 k- Nearest Neighbour ....................................................... 144
6.3.3.6 Classication and Regression Tree .................................145
6.3.4.1 Principal Component Regression ....................................145
6.3.4.2 Partial Least Squares Regression ....................................146
1, *
and Rachel Armitage
2
DOI: 10.1201/9781003270461-6
131
132
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Quantitative and Qualitative Determination of Counterfeit Drugs
6.4 Applications of IR Techniques for the Detection of Counterfeit
and Substandard Medicines .......................................................................146
6.4.1 Near- Infrared Spectroscopy Applications .....................................147
6.4.2 Mid- Infrared Spectroscopy Applications ......................................157
6.5 Conclusion ................................................................................................. 160
6.6 In memoriam: Dr Graham Lawson ...........................................................161
6.7 Acknowledgments ..................................................................................... 161
References ...........................................................................................................161
6.1 INTRODUCTION
Medicine quality is of paramount importance for the safety of patients and
fundamental to the success of health interventions. Counterfeit and substandard
medicines constitute a growing public health and patient safety problem worldwide,
particularly in low- income countries (LIC) and low to middle- income countries
(LMIC). The growth in international trade together with internet sales have placed
signicant pressure on the assurance of pharmaceutical supply chain integrity in
high- income countries (HIC). Counterfeit (falsied) medicines are deliberately and
fraudulently produced and labelled, with packaging that is often indistinguishable
from the genuine products, making them difcult to identify without running
detection tests on the contents of the pharmaceutical dosage form. Substandard
medicines result from poor manufacturing and quality assurance processes, as
well as inadequate storage conditions, and reach the public due to poor regulatory
controls or weak pharmaceutical governance (Sammons and Choonara, 2017). On
the market, substandard and counterfeit medicines claim to be something they are
not. These poor- quality pharmaceutical products are rarely efcacious and can lead
to disastrous health consequences, including treatment failure, serious adverse drug
reactions, disability and even death (WHO, 2017; Ghanem 2019). Additionally, they
lead to unintentional medication nonadherence (Tanna and Lawson, 2016), increase
the risk of drug resistance, undermine the public’s condence in healthcare systems
and add to national economic burdens (WHO, 2017; Ghanem 2019). According
to the World Health Organization (WHO), one in ten medical products in LMIC
are substandard or falsied (WHO, 2017) although more recent reports advocate
that approximately 40%– 70% of medicines being sold in Africa are thought to be
counterfeit or substandard (Bolla et al., 2020; Koech et al., 2020; Mwai 2020). The
risks to patients are also signicantly increased when medicines are purchased
from unregulated websites, social media platforms and smartphone applications
(WHO, 2018). Furthermore, there is considerable evidence that the COVID- 19
pandemic has heightened the trade of counterfeit medicines, especially in LIC and
LMIC, and this public healthcare problem is predicted to get worse (Newton et al.,
2020; Waffo Tchounga et al., 2021). This rise is attributed to the major disruption
in pharmaceutical supply chains and regular testing protocols due to national
lockdowns, which has led to an increase in demand for low- cost medicines and an
open market place for counterfeit medicines (Tesfaye et al., 2020).
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IR Spectroscopic Tools in Fight Against Counterfeit Medicines
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The absence of the active pharmaceutical ingredient (API) or incorrect amounts
of API are the main problems identied with counterfeit and substandard medicines,
although they may include pharmaceutical products with the wrong ingredient(s),
toxic impurities, dissolution failure, and fake packaging (Almuzaini et al., 2013).
Generic and branded medicines for communicable and life- threatening diseases
such as HIV/ AIDS, tuberculosis and malaria, as well as those for chronic diseases
such as cardiovascular disease, diabetes mellitus and cancer, have become the prime
target of such poor- quality medicines (Alghannam et al., 2014). In Africa, due to
the high burden of infectious diseases, counterfeit and substandard antibiotics are
also widespread in the market (Koech et al., 2020). Nearly one in ve antimalarials
circulating in LMIC are counterfeit or substandard (Mackey 2018; Beargie et al.,
2019). According to the WHO, there has also been an increase in counterfeit
medicines related to COVID- 19, including antiviral medicines and chloroquine
(Cooper et al., 2020). In HIC, lifestyle drugs used to treat erectile dysfunction
and weight loss and anabolic products have been extensively targeted (Rebiere
et al., 2017). In recent years, biotechnology drugs, including vaccines, have been
reported to be counterfeit (Janvier et al., 2018; Jarret et al., 2020; Srivastava 2021).
This public health problem is not limited to expensive medicines, as conterfeits
of low- priced medicines can still make a prot for criminals as long as the sales
volume are high (Lawson et al., 2018) – hence cutting prices for licensed medicines
will not provide a solution to this rising healthcare problem.
Given the high humanistic and economic cost associated with counterfeit
and substandard medicines globally, there is a pressing need for the routine
surveillance of pharmaceutical products in the pharmaceutical supply chain and at
border controls to determine the authenticity of the products. The early detection
of counterfeit and substandard medicines in a country will reduce the risk of these
poor- quality products being consumed by patients. A variety of technologies from
analytical chemistry can be used for surveillance (Rebiere et al., 2017; Bolla
et al., 2020; Bakker- ‘t Hart et al., 2021); however, it remains a major challenge in
LIC and LMIC due to limited resources and the lack of infrastructure and trained
personnel. Analytical technologies vary considerably in characteristics that impact
on their suitability for routine surveillance of medicines in these low- resource
countries. Historically, validated pharmacopoeia approved analytical methods
or non- validated inhouse procedures when pharmacopeial methods do not exist,
have been employed by LIC and LMIC medicines quality control laboratories for
determining the authenticity of medicines. In using this medicines authentication
approach in low- resource countries, there are often signicant delays between
collection of suspicious medicines and conrmation of their poor quality, with harm
spreading unchecked in the interim (Vickers et al., 2018). Techniques such as highperformance liquid chromatography (HPLC) with ultraviolet (UV) detection are
used, which are destructive, time- consuming due to complex sample preparation
steps, and expensive because they require large volumes of expensive solvents.
Additionally, analytical technology requires well- trained personnel and wellequipped laboratories, which are not readily available in LIC and LMIC (Lawson
134
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Quantitative and Qualitative Determination of Counterfeit Drugs
et al., 2018). Simple analytical techniques requiring little or no sample preparation
prior to analysis help to speed up analysis time and, thus, would be apt for rstline analysis of counterfeit medicines (Kovacs et al., 2014). Cost- effectiveness and
portability are important features to consider when selecting analytical techniques
for screening counterfeit and substandard medicines. Cheaper methods (in terms of
cost of production and maintenance) will make the techniques more accessible to a
wide range of users globally and, therefore, facilitate quicker analysis at different
points in the pharmaceutical supply chain. Portability of the analytical equipment
is also important in screening for counterfeit and substandard medicines in order
to ensure ease of use in the eld or at the point of sale of the medicines. The speed
of analysis, cheaper costs, portability, and simplicity of the technique employed
in the screening of medicines will go a long way in facilitating in- eld analysis
of medicines especially in LIC and LMIC. Due to the many constraints faced by
low- resource countries, not all suspicious medicines are quality tested. Hence,
there is an urgent need to empower LIC and LMIC ofcials at all levels of the
pharmaceutical supply chain with user- friendly, low- cost, robust, non- destructive,
and handheld or portable screening devices for the rapid detection of poor- quality
medicines. Infrared (IR) spectroscopy- based devices tting these criteria (Wilson
et al., 2017; Vickers et al., 2018) could transform LIC and LMIC healthcare systems’
medicine supply chains, providing assurance to health services and consumers,
while damaging the protability of counterfeit drug syndicates. If a pharmaceutical
product is deemed poor- quality based on an initial IR spectroscopy screening in the
eld, it can be subjected to further laboratory testing using a conrmatory method,
such as ambient ionisation mass spectrometry, to provide information about its
authenticity.
Mid- infrared (MIR) spectroscopy and near- infrared (NIR) spectroscopy are
versatile vibrational spectroscopy techniques, which can be used on solid or liquid
samples and have found widespread application over the past two decades for the
rapid screening of medicines. With spectroscopic- based methods, the excitation of
fundamental molecular rotations or vibrations gives rise to unique spectra for the
individual samples. The fundamental principles of these spectroscopy techniques
are explained in Section 6.2. These fast and cost- effective IR techniques, which
do not require consumables when combined with a spectral library, can provide
conclusive information about pharmaceutical samples, and are ideally suited
for both qualitative and quantitative analyses. Qualitative tests demonstrate the
presence or absence of a specic API or component, while quantitative tests
are able to conrm the levels of the API(s) in the sample (Kovacs et al., 2014).
Additionally, workow- based approaches can be implemented with these IR
spectroscopy devices to enable inexperienced users to perform the analysis. When
combined with classication chemometric algorithm(s), these MIR and NIR
spectroscopy techniques can be used to verify the identity of a sample and detect
counterfeit/ substandard or suspect medicines. The chemometric tools employed
with qualitative and quantitative MIR and NIR spectroscopy analyses are detailed
in Section 6.3. Advances in sampling techniques, chemometric data analysis tools,
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IR Spectroscopic Tools in Fight Against Counterfeit Medicines
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ruggedness, and MIR and NIR spectroscopy instrument portability have allowed
easy analysis of a broad range of pharmaceutical samples and the application of
MIR and NIR spectroscopy to rapidly identify counterfeit and/ or substandard
medicines are reviewed and discussed in Section 6.4. In Section 6.5 the future
directions for the application of IR spectroscopy devices for the rapid screening of
counterfeit and substandard medicines are anticipated.
6.2 FUNDAMENTALS OF INFRARED SPECTROSCOPY
The measurement of absorption of IR radiation brought about by changes in
molecular vibrations within molecules, gives rise to IR spectroscopy. The IR region
of the electromagnetic spectrum encompasses radiation with wavenumbers in the
range of about 12,800– 30 cm
- 1
. Depending on the wavelength of this radiation,
ngerprint spectra of molecular structures can be obtained. This data provides
information on the structure of the molecule and, in particular, the nature of the
functional groups present in the sample. The relationship of the different forms
of IR analytical techniques to the rest of the electromagnetic (EM) spectrum are
shown in Figure 6.1.
6.2.1 near- infrared SpectroScopy
Near- infrared (NIR) spectroscopy is a high- energy vibrational technique, covering
the transition from the visible spectral range to the MIR region. The NIR region
was rst discovered by William Herschel in the 1800s, but it was not until the
FIGURE 6.1 Electromagnetic spectrum and infrared region.
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1950s that the spectroscopy technique was rst used for analytical applications
(Pasquini 2018). This rapid and non- destructive technique can be used to
analyse pharmaceuticals with little or no sample preparation (Roggo et al., 2007;
Lohumi et al., 2015; Si et al., 2021). The non- destructive nature of the technique
Quantitative and Qualitative Determination of Counterfeit Drugs
allows samples to be subsequently analysed by other analytical techniques, or if
acquisition is through the packaging, there is a possibility to return the samples
into circulation (Roggo et al., 2007; Rodionova et al., 2018). Spectral data can
be obtained through packaging materials, including glass and blister packaging
(Krakowska et al., 2016).
For NIR spectroscopic analysis, samples are illuminated with a broad spectrum
of NIR radiation that can be absorbed, transmitted, reected, or scattered by
the sample (Figure 6.2). The use of a prism or grating separates the frequencies
emitted from the source, while a detector simultaneously measures the amount of
energy that passes through (Lohumi et al., 2015). NIR spectroscopy uses overtone
and recombination bands in the range of 750– 2500 nm (12,820– 4000 cm
- 1
) to
determine the structure of the sample (Krakowska et al., 2016; Pasquini 2018). NIR
spectra comprise of overtones and combination bands that are mainly attributed to
hydrogen vibrations (CH, NH, OH) (Reich 2005; Lohumi et al., 2015). Absorption
of NIR radiation in the matter is usually not uniform and depends on the molecular
structure and number of bonds in the molecule (see Figure 6.2).
FIGURE 6.2 Schematic of a near- infrared spectrometer.
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IR Spectroscopic Tools in Fight Against Counterfeit Medicines
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The properties of a sample can be investigated using different spectral modes,
these assorted modes offer a variety of information about the sample. The
interaction can be reectance (specular and diffuse), transmittance, interactance,
and transreectance (Pasquini 2018). The spectral mode employed depends on the
physical properties of the sample. Reectance or interactance is generally used for
solid samples, whereas transmission is used for liquids. Thin or clear samples are
analysed using transreectance (Lohumi et al., 2015). The most common mode
applied to solid samples is diffuse reectance (Pasquini 2018); this occurs when
the measured light is reected from a rough surface. The data generated contains
information about the chemical and physical properties of the sample (Lohumi
et al., 2015). The spectral data produced provides molecular information not only
of the API(s), but also of other excipients present from a single measurement
(Laasonen et al., 2004; Baer et al., 2007). While benchtop NIR spectrometers have
been widely studied for assessing the quality of pharmaceuticals, portable and
handheld versions are being investigated for this application. The ability of portable
NIR spectrometers allows in the in- eld real time screening to be performed.
A disadvantage of NIR spectroscopy is that only broad bands are observed and
the spectra can be difcult to interpret due to overlapping signals (Roggo et al.,
2007). The observed absorbance bands are the result of overtones from different
functional groups within the sample analysed. Therefore, molecules with a similar
chemical structure may be difcult to distinguish. With NIR spectroscopy, mixture
analysis can present spectra with superimposed absorptions and compounds
and may only be recognised if they have a unique functional group (Baer et al.,
2007). Furthermore, careful calibration and acquisition of standard spectra of APIs
and excipients is required in order to ensure accurate quantitative identication
(Pasquini 2018). NIR spectroscopy may also not be sensitive enough to detect
slight manufacturing differences between pharmaceutical samples (Rebiere et al.,
2021). It has been implied that storage conditions of pharmaceuticals should be
considered when using NIR spectroscopy for their analysis since NIR spectra
are sensitive to samples that absorb water from the atmosphere (de Peinder et al.,
2008; Moffat et al., 2010). The lack of specicity of the data in an NIR spectrum
combined with the complexity of the source of the signal means that chemometrics
approaches are always required to determine the sample composition and to support
the authentication of a pharmaceutical product (Roggo et al., 2007).
6.2.2 mid- infrared SpectroScopy
The electromagnetic energy of molecular vibration is dened as the infrared region,
or MIR, in the range of from 4000– 400 cm
- 1
. MIR spectroscopy has benetted
greatly from the development of microcomputer and spectroscopic approaches
based on Fourier transform, thus giving rise to Fourier transform infrared (FTIR).
FTIR spectroscopy is a prominent vibrational technique and is a sophisticated
tool in the spectral analysis of organic compounds (Cheng et al., 2010; Jamwal
et al., 2021). FTIR spectroscopy is used to obtain structural information about a
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