Spontaneous Crystallinity Loss of Drugs in the Disordered Regions of Poly(Ethylene Oxide) in the Presence of Water

Amorphous and Co-Amorphous Olanzapine Stability in Formulations Intended for Wet Granulation and Pelletization

The preparation of amorphous and co-amorphous systems (CAMs) effectively addresses the solubility and bioavailability issues of poorly water-soluble chemical entities. However, stress conditions imposed during common pharmaceutical processing (e.g., tableting) may cause the recrystallization of the systems, warranting close stability monitoring throughout production. This work aimed at assessing the water and heat stability of amorphous olanzapine (OLZ) and OLZ-CAMs when subject to wet granulation and pelletization. Starting materials and products were characterized using calorimetry, diffractometry and spectroscopy, and their performance behavior was evaluated by dissolution testing. The results indicated that amorphous OLZ was reconverted back to a crystalline state after exposure to water and heat; conversely, OLZ-CAMs stabilized with saccharin (SAC), a sulfonic acid, did not show any significant loss of the amorphous content, confirming the higher stability of OLZ in the CAM. Besides resistance under the processing conditions of the dosage forms considered, OLZ-CAMs presented a higher solubility and dissolution rate than the respective crystalline counterpart. Furthermore, in situ co-amorphization of OLZ and SAC during granule production with high fractions of water unveils the possibility of reducing production steps and associated costs.

Combining X-ray and NMR Crystallography to Explore the Crystallographic Disorder in Salbutamol Oxalate

Salbutamol is an active pharmaceutical ingredient commonly used to treat respiratory distress and is listed by the World Health Organization as an essential medicine. Here, we establish the crystal structure of its oxalate form, salbutamol oxalate, and explore the nature of its crystallographic disorder by combined X-ray crystallography and ¹³C cross-polarization (CP) magic-angle spinning (MAS) solid-state NMR. The *C-OH chiral center of salbutamol (note that the crystal structures are a racemic mixture of the two enantiomers of salbutamol) is disordered over two positions, and the tert-butyl group is rotating rapidly, as revealed by ¹³C solid-state NMR. The impact of crystallization conditions on the disorder was investigated, finding variations in the occupancy ratio of the *C-OH chiral center between single crystals and a consistency across samples in the bulk powder. Overall, this work highlights the contrast between investigating crystallographic disorder by X-ray diffraction and solid-state NMR experiment, and gauge-including projector-augmented-wave (GIPAW) density functional theory (DFT) calculations, with their combined use, yielding an improved understanding of the nature of the crystallographic disorder between the local (i.e., as viewed by NMR) and longer-range periodic (i.e., as viewed by diffraction) scale.

Recent Technologies for Amorphization of Poorly Water-Soluble Drugs

Amorphization technology has been the subject of continuous attention in the pharmaceutical industry, as a means to enhance the solubility of poorly water-soluble drugs. Being in a high energy state, amorphous formulations generally display significantly increased apparent solubility as compared to their crystalline counterparts, which may allow them to generate a supersaturated state in the gastrointestinal tract and in turn, improve the bioavailability. Conventionally, hydrophilic polymers have been used as carriers, in which the amorphous drugs were dispersed and stabilized to form polymeric amorphous solid dispersions. However, the technique had its limitations, some of which include the need for a large number of carriers, the tendency to recrystallize during storage, and the possibility of thermal decomposition of the drug during preparation. Therefore, emerging amorphization technologies have focused on the investigation of novel amorphous-stabilizing carriers and preparation methods that can improve the drug loading and the degree of amorphization. This review highlights the recent pharmaceutical approaches utilizing drug amorphization, such as co-amorphous systems, mesoporous particle-based techniques, and in situ amorphization. Recent updates on these technologies in the last five years are discussed with a focus on their characteristics and commercial potential.

Evaluation of tableting performance of Poly (ethylene oxide) in abuse-deterrent formulations using compaction simulation studies

Poly (ethylene oxide) (PEO) has been widely used in abuse-deterrent formulations (ADFs) to increase tablet hardness. Previous studies have shown that formulation variables such as processing conditions and particle size of PEO can affect ADF performance in drug extraction efficiency. This work aims to understand the effect of PEO grades and sources on the compaction characteristics of model ADFs. PEOs from Dow Chemical and Sumitomo Chemical with different molecular weights were examined using a Styl'One compaction simulator at slow, medium, and fast tableting speeds. Particle-size distribution, thermal behavior, tabletability, compressibility using the Heckel model, compactibility, and elastic recovery were determined and compared between the neat PEOs and model ADFs. Multivariate linear regression was performed to understand the effect of compression conditions and PEO grades and sources. Our results show that neat PEOs with high molecular weight exhibit high tabletability. The source of neat PEOs contributes to the difference in tabletability, out-die compressibility, compactibility, and elastic recovery. However, the influence of the PEO source on tabletability and compactibility decreases after adding the model drug. In our model ADFs, tablets using PEOs with high molecular weight have high crushing strength, and tablets using PEOs from Dow Chemical display low elastic recovery.

Stability and bioavailability of diltiazem/polyethylene oxide matrix tablets

The aim of this study was to prepare and evaluate in vitro and in vivo; Diltiazem-Hydrochloride (DTZ) in sustained-release matrix tablets. Stability of DTZ tablets prepared with polyethylene oxide (MWs 900 000, 4 000 000, and 8 000 000) with or without addition of electrolytes was carried-out for 1-month, under short-term storage at 40 °C/75% RH. Stability was evaluated by DTZ content, DSC and drug release using the Flow-Through Cell (USP # IV). The majority of stored tablets were stable for 1-month under short-term storage with respect to DTZ content and drug release. DSC curves of stored samples showed appearance of new exothermic peak after 1-month storage at 40 °C/75% RH, which was not observed after 5 years storage at room temperature. A selected formula was tested in vivo against reference product on eight healthy human volunteers. DTZ-plasma profiles were different between the two formulae. However, no statistically significant differences were detected between C_max, AUC_0-48 and AUC_0-∞. The two products were therapeutically in-equivalent, as 90% confidence intervals "T/R" were 88.82-205.76, 91.40-139.94, and 93.73-134.97 for C_max, AUC_0-48 and AUC_0-∞, respectively. This study highlighted possible differences observed between the two regimes frequently applied for stability testing.

An Insight Into the Impact of Polymers on the Hydrate Conversion of Olanzapine Form I in Aqueous Suspensions

The potential of polyethyleneglycol (PEG), polyvinylpyrrolidone (PVP), and hydroxypropylcellulose (HPC) to inhibit the hydration of olanzapine (OLZ) in aqueous environments was assessed. OLZ Form I (OLZ) suspended in water (A) or in aqueous polymer solutions (2%, 0.2%, 0.02%, and 0.002%) (PEG 6000 [B], PEG 40,000 [C], HPC LF [D], or PVP K30 [E]). Filtered samples were analyzed by different techniques (X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, ¹H-nuclear magnetic resonance spectroscopy). OLZ hydration showed to be faster in water than in PEG solutions, regardless of the polymer molecular weight. OLZ in D and E suspensions remained anhydrous at concentrations of 2%-0.02%. The NMR measurements revealed that all of these polymers were able to establish hydrogen bonds with the OLZ molecule and increased its saturation solubility, but only D and E showed to increase the wettability of the OLZ particles due to binding of these polymers to the surface of hydrate nuclei/first crystals OLZ crystals. This study provided an insight into the mechanisms of OLZ hydrate protection by polymers. It confirmed the advantage of using PVP K30 or HPC LF in wet granulation in concentrations as low as 0.02% to prevent formation of OLZ hydrates, due to the combined effect of H-bond ability and the strong bonding of these polymers to the surface of the crystals.

Amorphization within the tablet: Using microwave irradiation to form a glass solution in situ

In situ amorphization is a concept that allows to amorphize a given drug in its final dosage form right before administration. Hence, this approach can potentially be used to circumvent recrystallization issues that other amorphous formulation approaches are facing during storage. In this study, the feasibility of microwave irradiation to prepare amorphous solid dispersions (glass solutions) in situ was investigated. Indomethacin (IND) and polyvinylpyrrolidone K12 (PVP) were tableted at a 1:2 (w/w) ratio. In order to study the influence of moisture content and energy input on the degree of amorphization, tablet formulations were stored at different relative humidity (32, 43 and 54% RH) and subsequently microwaved using nine different power-time combinations up to a maximum energy input of 90kJ. XRPD results showed that up to 80% (w/w) of IND could be amorphized within the tablet. mDSC measurements revealed that with increasing microwaving power and time, the fractions of crystalline IND and amorphous PVP reduced, whereas the amount of in situ formed IND-PVP glass solution increased. Intrinsic dissolution showed that the dissolution rate of the microwaved solid dispersion was similar to that of a quench cooled, fully amorphous glass solution even though the microwaved samples contained residual crystalline IND.

The effects of polymer carrier, hot melt extrusion process and downstream processing parameters on the moisture sorption properties of amorphous solid dispersions

OBJECTIVE

The aim of this study was to evaluate the effect of polymer carrier, hot melt extrusion and downstream processing parameters on the water uptake properties of amorphous solid dispersions.

METHODS

Three polymers and a model drug were used to prepare amorphous solid dispersions utilizing the hot melt extrusion technology. The sorption-desorption isotherms of solid dispersions and their physical mixtures were measured by the dynamic vapour sorption system, and the effects of polymer hydrophobicity, hygroscopicity, molecular weight and the hot melt extrusion process were investigated. Fourier transform infrared (FTIR) imaging was performed to understand the phase separation driven by the moisture.

KEY FINDINGS

Solid dispersions with polymeric carriers with lower hydrophilicity, hygroscopicity and higher molecular weight could sorb less moisture under the high relative humidity (RH) conditions. The water uptake ability of polymer-drug solid dispersion systems were decreased compared with the physical mixture after hot melt extrusion, which might be due to the decreased surface area and porosity. The FTIR imaging indicated that the homogeneity of the drug molecularly dispersed within the polymer matrix was changed after exposure to high RH.

CONCLUSION

Understanding the effect of formulation and processing on the moisture sorption properties of solid dispersions is essential for the development of drug products with desired physical and chemical stability.

Unintended and in situ amorphisation of pharmaceuticals

Amorphisation of poorly water-soluble drugs is one approach that can be applied to improve their solubility and thus their bioavailability. Amorphisation is a process that usually requires deliberate external energy input. However, amorphisation can happen both unintentionally, as in process-induced amorphisation during manufacturing, or in situ during dissolution, vaporisation, or lipolysis. The systems in which unintended and in situ amorphisation has been observed normally contain a drug and a carrier. Common carriers include polymers and mesoporous silica particles. However, the precise mechanisms by which in situ amorphisation occurs are often not fully understood. In situ amorphisation can be exploited and performed before administration of the drug or possibly even within the gastrointestinal tract, as can be inferred from in situ amorphisation observed during in vitro lipolysis. The use of in situ amorphisation can thus confer the advantages of the amorphous form, such as higher apparent solubility and faster dissolution rate, without the disadvantage of its physical instability.

Reduction and control of domain spacing by additive inclusion: morphology and orientation effects of glycols on microphase separated PS-b-PEO

Cylindrical phase polystyrene-b-polyethylene oxide (PS-b-PEO) block copolymer (BCP) was combined with lower molecular weight poly/ethylene glycols at different concentrations and their effect on the microphase separation of BCP thin films were studied. Well-ordered microphase separated, periodic nanostructures were realized using a solvent annealing approach for solution cast thin films. By optimizing solvent exposure time, the nature and concentration of the additives etc. the morphology and orientation of the films can be controlled. The addition of the glycols to PS-b-PEO enables a simple method by which the microdomain spacing of the phase separated BCP can be controlled at dimensions below 50 nm. Most interestingly, the additives results in an expected increase in domain spacing (i.e. pitch size) but in some conditions an unexpected reduction in domain spacing. The pitch size achieved by modification is in the range of 16-31 nm compared to an unmodified BCP system which exhibits a pitch size of 25 nm. The pitch size modification achieved can be explained in terms of chemical structure, solubility parameters, crystallinity and glass transition temperature of the PEO because the additives act as PEO 'stress cracking agents' whereas the PS matrix remains chemically unaffected.

In situ amorphisation of indomethacin with Eudragit® E during dissolution

In this study, the possibility of utilising in situ crystalline-to-amorphous transformation for the delivery of poorly water soluble drugs was investigated. Compacts of physical mixtures of γ-indomethacin (IMC) and Eudragit® E in 3:1, 1:1 and 1:3 (w/w) ratios were subjected to dissolution testing at pH 6.8 at which IMC but not the polymer is soluble. Compacts changed their colour from white to yellow indicating amorphisation of IMC. X-ray powder diffractometry (XRPD) confirmed the amorphisation and only one glass transition temperature was observed (58.1 °C, 54.4 °C, and 50.1 °C for the 3:1, 1:1 and 1:3 (w/w) drug-to-polymer ratios, respectively). Furthermore, principal component analysis of infrared spectra resulted in clustering of in situ transformed samples together with quench cooled glass solutions for each respective ratio. Subsequent dissolution testing of in situ transformed samples at pH 4.1, at which the polymer is soluble but not IMC, led to a higher dissolution rate than for quench cooled glass solution at 3:1 and 1:1 ratios, but not for the 1:3 ratio. This study showed that crystalline drug can be transformed into amorphous material in situ in the presence of a polymer, leading to the possibility of administering drugs in the amorphous state without physical instability problems during storage.

Effect of laser irradiation on the stability of a photo-sensitive active pharmaceutical ingredient by Raman microscopy

This study was conducted to investigate the effect of laser beam irradiation from a novel non-confocal laser Raman microscope on the stability of a photo-sensitive drug. The non-confocal Raman microscopy, which irradiates a low-power unfocused laser beam on the surface of the samples by controlling of optical system, was applied to characterize the stability of nifedipine as a photo-sensitive drug model. The time-dependent changes in the Raman spectra of nifedipine were monitored in order to evaluate the degradation of nifedipine during laser irradiation. The results were compared with the Raman spectra measured by using the confocal laser Raman microscopy which irradiates a low-power focused laser beam. The intensity of some peaks in the confocal Raman spectra significantly decreased depending on the irradiation-time length, compared to the non-confocal Raman macroscopic analysis. The photodegradation of nifedipine caused by the laser irradiation followed the first-order kinetics. The degradation rate constants of nifedipine with the non-confocal analysis were lower than those of nifedipine with the confocal analysis. Thus, the novel non-confocal laser Raman microscopy can be applied to reduce the degradation of the photo-sensitive drug during laser irradiation, and the results suggest that the non-confocal laser Raman microscopy will be a useful technique for the measuring of Raman spectra of photo-sensitive materials with a long-term exposure.

Analysis of solid-state transformations of pharmaceutical compounds using vibrational spectroscopy

Objectives

Solid-state transformations may occur during any stage of pharmaceutical processing and upon storage of a solid dosage form. Early detection and quantification of these transformations during the manufacture of solid dosage forms is important since the physical form of an active pharmaceutical ingredient can significantly influence its processing behaviour, including powder flow and compressibility, and biopharmaceutical properties such as solubility, dissolution rate and bioavailability.

Key findings

Vibrational spectroscopic techniques such as infrared, near-infrared, Raman and, most recently, terahertz pulsed spectroscopy have become popular for solidstate analysis since they are fast and non-destructive and allow solid-state changes to be probed at the molecular level. In particular, Raman and near-infrared spectroscopy, which require no sample preparation, are now commonly used coupled to fibreoptic probes and are able to characterise solid-state conversions in-line. Traditionally, uni- or bivariate approaches have been used to analyse spectroscopic data sets; however, recently the simultaneous detection of several solid-state forms has been increasingly performed using multivariate approaches where even overlapping spectral bands can be analysed.

Summary

This review discusses the applications of different vibrational spectroscopic techniques to detect and monitor solid-state transformations possible for crystalline polymorphs, hydrates and amorphous forms of pharmaceutical compounds. In this context, the theoretical basis of solid-state transformations and vibrational spectroscopy and common experimental approaches are described, including recent methods of data analysis.