FTIR microscopy and confocal Raman microscopy for studying lateral drug diffusion from a semisolid formulation

Neither too little nor too much: Finding the ideal proportion of excipients using confocal Raman and chemometrics

The applications of Raman imaging in pharmaceutical field are ever-increasing due its ability to obtain spatial and spectral information simultaneously, once it allows determine the chemical distribution of compounds. In this sense, it is used to study homogeneity, of paramount importance during the development of pharmaceutical formulations due to its relation to stability, safety and efficacy. Commonly, just surface is analyzed, but confocal Raman spectroscopy can also characterize the inner part of samples, allowing to determine phase separation in the early stages. In this sense, confocal 3D Raman microscopy was crucial to obtain the optimal proportion of Apifil®, Capryol® 90 and Transcutol® to promote controlled release of the local anesthetic butamben (BTB). 3D chemical maps were obtained by classical least squares (CLS) using pure compound spectra as S matrix, showing that chemical distribution throughout the material was different. Knowing that the composition of samples affects the homogeneity parameter, standard deviation and distributional homogeneity index (DHI) were used in mixture experimental design (DoE). From this analysis, it was revealed that a correct amount of Capryol® 90 enhances both miscibility and solubility. Furthermore, suitable miscibility was observed in two ratio proportions of excipients with a desirability of 0.783 and 0.742. These results unequivocally demonstrated that confocal Raman microscopy combined to DoE can bring pharmaceutical development to a higher level.

In situ Analytical Quality Control of chemotherapeutic solutions in infusion bags by Raman spectroscopy

Analytical Quality Control (AQC) in centralised preparation units of oncology centers is a common procedure relying on the identification and quantification of the prepared chemotherapeutic solutions for safe intravenous administration to patients. Although the use of Raman spectroscopy for AQC has gained much interest, in most applications it remains coupled to a flow injection analyser (FIA) requiring withdrawal of the solution for analysis. In addition to current needs for more rapid and cost-effective analysis, the risk of exposure of clinical staff to the toxic molecules during daily handling is a serious concern to address. Raman spectroscopic analysis, for instance by Confocal Raman Microscopy (CRM), could enable direct analysis (non-invasive) for AQC directly in infusion bags. In this study, 3 anticancer drugs, methotrexate (MTX), 5-fluorouracil (5-FU) and gemcitabine (GEM) have been selected to highlight the potential of CRM for withdrawal free analysis. Solutions corresponding to the clinical range of each drug were prepared in 5% glucose and data was collected from infusion bags placed under the Raman microscope. Firstly, 100% discrimination has been obtained by Partial Least Squares Discriminant Analysis (PLS-DA) confirming that the identification of drugs can be performed. Secondly, using Partial Least Squares Regression (PLSR), quantitative analysis was performed with mean % error of predicted concentrations of respectively 3.31%, 5.54% and 8.60% for MTX, 5-FU and GEM. These results are in accordance with the 15% acceptance criteria used for the current clinical standard technique, FIA, and the Limits of Detection for all drugs were determined to be substantially lower than the administered range, thus highlighting the potential of confocal Raman spectroscopy for direct analysis of chemotherapeutic solutions.

Dermatologic reactions to disinfectant use during the COVID-19 pandemic

Infection preventive practice of using disinfectants against SARS-CoV-2 has become the new normal due to the COVID-19 pandemic. Although disinfectants may not be applied directly to the human body, it remains at high risk of exposure including close skin contact on disinfected surfaces or during handling. This dermal contact, on a regular basis, can induce hazardous skin reactions like irritation, inflammation, and burning in severe conditions. Disinfectants are germicide chemicals that can penetrate the skin and create skin reactions that are usually regarded as irritant and allergic contact dermatitis. More importantly, disinfectants can react with skin components (proteins and lipids) to facilitate their skin penetration and disrupt the skin barrier function. Whereas the antimicrobial actions of disinfectants are well understood, much less is known regarding their dermatologic reactions, including but not limited to irritation and hypersensitivity. We reviewed the skin reactions created by those disinfectants against SARS-CoV-2 approved by the European Chemical Agency and the US Environmental Protection Agency.

Applications of Fourier transform infrared spectroscopy to pharmaceutical preparations

Introduction: Various pharmaceutical preparations are widely used for clinical treatment. Elucidation of the mechanisms of drug release and evaluation of drug efficacy in biological samples are important in drug design and drug quality control.Areas covered: This review classifies recent applications of Fourier transform infrared (FTIR) spectroscopy in the field of medicine to comprehend drug release and diffusion. Drug release is affected by many factors of preparations, such as drug delivery system and microstructure polymorphism. The applications of FTIR imaging and nano-FTIR technique in biological samples lay a foundation for studying drug mechanism in vivo.Expert opinion: FTIR spectroscopy meets the research needs on preparations to understand the processes and mechanisms underlying drug release. The combination of attenuated total reflectance-FTIR imaging and nano-FTIR accompanied by chemometrics is a potent tool to overcome the deficiency of conventional infrared detection. FTIR shows an enormous potential in drug characterization, drug quality control, and bio-sample detection.

Raman mapping of fentanyl transdermal delivery systems with off-label modifications

Raman mapping is a powerful and emerging tool in characterization of pharmaceuticals and provides non-destructive chemical and structural identification with minimal sample preparation. One pharmaceutical form that is suitable but has not been studied in-depth with Raman mapping is transdermal delivery systems (TDS). TDS are dosage forms designed to deliver a therapeutically effective amount of active pharmaceutical ingredient (API) across a patient's skin. To enhance drug delivery through the skin, the API in the formulation is often close to a saturated or supersaturated state. Thus, improper use or off-label modifications can lead to occurrence of unwanted API changes, specifically, crystallization over time. Here, off-label modifications were mimicked on a set of fentanyl drug-in-adhesive TDS sold on the U.S. market by four different manufacturers via die cutting, and then the die cut TDS were investigated through confocal Raman mapping for structural and chemical changes. Using Multivariate Curve Resolution (MCR), not only was morphological and chemical characterization of transdermal systems provided, but also fentanyl crystals in certain products due to off-label modifications were identified. The chemometric model used in analysis of Raman maps allowed precise identification of fentanyl as the crystalline material as confirmed by the hit-quality-index correlation of component spectra from the chemometric model with library spectra of a fentanyl reference standard. The results show that confocal Raman mapping with MCR can be utilized in assessing pharmaceutical quality of TDS. This method has the potential to be widely used in characterization of such systems as an alternative to existing techniques.

Imaging Analysis Enables Differentiation of the Distribution of Pharmaceutical Ingredients in Tacrolimus Ointments

We demonstrated the difference in the distribution state of pharmaceutical ingredients between tacrolimus (TCR) original ointment and six kinds of generic medicines. Two-dimensional imaging and depth analysis using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy and confocal Raman microscopy were used, in addition to the evaluation of pharmaceutical properties, including spreading properties, rheological properties, and amount of solvent. The solvents, such as propylene carbonate and triacetin, in TCR ointments formed liquid droplets and dispersed in hydrocarbon oils. Waxes, white beeswax and beeswax, formed other domains. Confocal Raman microscopy could detect liquid droplet size without coalescence of that on germanium or glass surfaces. The combination of ATR FT-IR and confocal Raman imaging would be a powerful tool to reveal the size and shape of liquid droplets of pharmaceutical ingredients in semisolid formulations.

Methods to Evaluate Skin Penetration In Vitro

Dermal and transdermal drug therapy is increasing in importance nowadays in drug development. To completely utilize the potential of this administration route, it is necessary to optimize the drug release and skin penetration measurements. This review covers the most well-known and up-to-date methods for evaluating the cutaneous penetration of drugs in vitro as a supporting tool for pharmaceutical research scientists in the early stage of drug development. The aim of this article is to present various experimental models used in dermal/transdermal research and summarize the novel knowledge about the main in vitro methods available to study skin penetration. These techniques are: Diffusion cell, skin-PAMPA, tape stripping, two-photon microscopy, confocal laser scanning microscopy, and confocal Raman microscopic method.

Raman imaging of drug delivery systems

This review article includes an introduction to the principals of Raman spectroscopy, an outline of the experimental systems used for Raman imaging and the associated important considerations and limitations of this method. Common spectral analysis methods are briefly described and examples of interesting published studies which utilised Raman imaging of pharmaceutical and biomedical devices are discussed, along with summary tables of the literature at this point in time.

Applications of Raman spectroscopy in skin research--From skin physiology and diagnosis up to risk assessment and dermal drug delivery

In the field of skin research, confocal Raman microscopy is an upcoming analytical technique. Substantial technical progress in design and performance of the individual setup components like detectors and lasers as well as the combination with confocal microscopy enables chemically selective and non-destructive sample analysis with high spatial resolution in three dimensions. Due to these advantages, the technique bears tremendous potential for diverse skin applications ranging from the analysis of physiological component distribution in skin tissue and the diagnosis of pathological states up to biopharmaceutical investigations such as drug penetration kinetics within the different tissue layers. This review provides a comprehensive introduction about the basic principles of Raman microscopy highlighting the advantages and considering the limitations of the technique for skin applications. Subsequently, an overview about skin research studies applying Raman spectroscopy is given comprising various in vitro as well as in vivo implementations. Furthermore, the future perspective and potential of Raman microscopy in the field of skin research are discussed.

Topically applied ceramide accumulates in skin glyphs

Ceramides (CERs), structural components of the stratum corneum (SC), impart essential barrier properties to this thin outer layer of the epidermis. Variations in CER species within this layer have been linked to several skin diseases. A recent proliferation of CER-containing topical skin-care products warrants the elucidation of CER penetration profiles in both healthy and diseased skin. In the current study, the spatial distributions of CER concentration profiles, following topical application of two species of CER, were tracked using infrared imaging. Suspensions of single-chain perdeuterated sphingosine and phytosphingosine CER in oleic acid were applied, in separate experiments, to the surface of healthy intact ex vivo human skin using Franz diffusion cells. Following either a 24- or 48-hour incubation period at 34°C, infrared images were acquired from microtomed skin sections. Both CER species accumulated in glyph regions of the skin and penetrated into the SC, to a limited extent, only in these regions. The concentration profiles observed herein were independent of the CER species and incubation time utilized in the study. As a result, a very heterogeneous, sparse, spatial distribution of CERs in the SC was revealed. In contrast, oleic acid was found to be fairly homogeneously distributed throughout the SC and viable epidermis, albeit at lower concentrations in the latter. A more uniform, lateral distribution of CERs in the SC would likely be important for barrier efficacy or enhancement.

Advances in the bioanalytical study of drug delivery across the skin

The study of a drug's dermal penetration profile provides important pharmaceutical data for the rational development of topical and transdermal delivery systems because the skin is a broadly used delivery route for local and systemic drugs and a potential route for gene therapy and vaccines. Monitoring drug penetration across the skin and quantifying its levels in different skin layers have been constant challenges due to the detection limitations of the available techniques, as well as the inherent interference in this tissue. This review explores and discusses several bionalytical methods that are indispensable tools to study drugs across the skin. In addressing the main topic, we structure the review highlighting the skin as an important route of drug administration and its structure, skin membrane models most used and its properties, in vitro and in vivo assays most used in the study of drug delivery to the skin, the techniques for processing the skin for subsequent analysis by bioanalytical methods that have a theoretical and practical approach showing its applicability, limitations and also including examples of its use. This review has a comprehensive approach in order to help researchers design their experiments and update the applicability and advances in this area of expertise.

Monitoring caffeine and resveratrol cutaneous permeation by confocal Raman microspectroscopy

Dynamic follow-up of exogenous molecules permeation through the skin is one among many competing applications for confocal Raman microspectroscopy. Previous studies showed the feasibility of tracking actives through the skin; the next step should be recording in vivo kinetics. Thus, we conducted a study to evaluate the possibility of detecting low concentrations of caffeine and resveratrol solutions through the skin using confocal Raman microspectroscopy. After topical application of each active on the skin surface, Raman profiles were recorded over nine hours. The challenge was to pursuit these actives respecting the concentration used in some dermatological formulations. Molecules were successfully detected and kinetic profiles were registered over time. The heterogeneity of skin structure and the complexity of molecules diffusion were reflected through the kinetic results.

Characterization of the dynamic thickness of the aerobic layer during pig manure aerobic composting by Fourier transform infrared microspectroscopy

A new method for characterizing the aerobic layer thickness in pig manure based on Fourier transform infrared microspectroscopy (FTIRM) is presented to improve the anaerobic/aerobic co-process mechanism, to ensure adequate oxygen supply and, thus, minimize methane emissions during aerobic composting. Freeze-dried manure particles were microtomed into 10 μm thick sections; the spectral range, spectral resolution, and pixel dimensions in the transmission spectra were 4000-650 cm(-1), 16 cm(-1), and 6.25 × 6.25 μm, respectively. A mean spectrum of 16 scans was used for the second-derivative analysis with nine smoothing points. This is the first attempt at determining the oxidation profile of composting particles according to the radial variations in second-derivative spectra at 2856 and 1568 cm(-1), which are attributed to the reactants and products of the oxidation, respectively. In addition, an intermediate area is detected between the aerobic layer and anaerobic core. The experimental values of the aerobic layer thickness are consistent with the estimates, and an exponential increase is observed, which is influenced by multiple dynamic factors. However, the contribution of each factor to dynamic variations in the aerobic layer thickness should be investigated using available methods.

Infrared spectroscopic imaging tracks lateral distribution in human stratum corneum

PURPOSE

To demonstrate the efficacy of infrared (IR) spectroscopic imaging for evaluation of lateral diffusion in stratum corneum (SC) and for elucidation of intermolecular interactions between exogenous agents and SC constituents.

METHODS

In separate experiments, acyl chain perdeuterated oleic acid (OA-d) and deuterated dimethyl sulfoxide (DMSO-d) were applied to the surface of isolated human SC. The lateral distribution of permeant concentrations was monitored using the time-dependence of IR images. Diffusion coefficients (D) were estimated from Fick's second law. Interactions between the exogenous agents and the SC were tracked from changes in CD2 and Amide I stretching frequencies.

RESULTS

Networked glyphs served as the major pathway for lateral distribution of OA-d. In glyph-poor regions, D values from 0.3-1 × 10(-8) cm(2)/s bracketed the OA-d data and apparently decreased with time. Although diffusion of DMSO-d is relatively fast compared to our experimental measurement time, the results suggest values of ~10(-7) cm(2)/s. OA-d spectral changes suggest penetration into the ordered lipids of the SC; DMSO-d penetration results in perturbation of SC keratin structure.

CONCLUSIONS

IR imaging provides concentration profiles, diffusion coefficients, and unique molecular level information about structural changes in the endogenous SC constituents and exogenous agents upon their mutual interaction. Transport along glyphs is the dominant mode of distribution for OA-d.

Physical signatures of drug transport through an artificial skin barrier--a proposed model and its validation

The objective of the present study is to better characterize the system acting as a model for the penetration of a pharmaceutical drug into the skin. With a new mathematical formalism, the transport of the drug (dithranol) from a semisolid vaseline suspension into an artificial membrane was described. In our novel approach, we have taken into account not only diffusion but also other effects dependent on chemical reactivity of drug, medium structure, and drug-matrix interactions. The transport equation was solved with two methods: the Laplace transform and the reflection-and-superposition. Despite the applied method, the three-dimensional calculations were found to be, in major parts, in good agreement with the experimental data resulting from the photoacoustic depth profiling. For the first time, from the depth profiling we were capable of estimating not only the diffusion coefficient but also other parameters of the permeation phenomenon as the pore velocity, the first and the zero order reaction rate coefficients.

Raman mapping of pharmaceuticals

Raman spectroscopy may be implemented through a microscope to provide fine scale axial and lateral chemical maps. The molecular structure of many drugs makes Raman spectroscopy particularly well suited to the investigation of pharmaceutical systems. Chemometric methods currently used to assess bulk Raman spectroscopic data are typically applied to Raman mapping data from pharmaceuticals; few reports exist where the spatial information inherent to a mapped dataset is used for the calculation of chemical maps. Both univariate and multivariate methods have been applied to Raman mapping data to determine the distribution of active pharmaceutical ingredients (APIs) in tablets, solid dispersions for increased solubility and controlled release devices. The ability to axially (depth) profile using Raman mapping has been used in studies of API penetration through membranes, cellular uptake of drug delivery liposomes, and initial API distribution and subsequent elution from coatings of medical devices. New instrumental developments will increase the efficiency of Raman mapping and lead to greater utilisation of Raman mapping for analyses of pharmaceutical systems.