Physicochemical stability of nitrofurantoin anhydrate and monohydrate under various temperature and humidity conditions

Formulation Strategies to Improve the Stability and Handling of Oral Solid Dosage Forms of Highly Hygroscopic Pharmaceuticals and Nutraceuticals

Highly hygroscopic pharmaceutical and nutraceutical solids are prone to significant changes in their physicochemical properties due to chemical degradation and/or solid-state transition, resulting in adverse effects on their therapeutic performances and shelf life. Moisture absorption also leads to excessive wetting of the solids, causing their difficult handling during manufacturing. In this review, four formulation strategies that have been employed to tackle hygroscopicity issues in oral solid dosage forms of pharmaceuticals/nutraceuticals were discussed. The four strategies are (1) film coating, (2) encapsulation by spray drying or coacervation, (3) co-processing with excipients, and (4) crystal engineering by co-crystallization. Film coating and encapsulation work by acting as barriers between the hygroscopic active ingredients in the core and the environment, whereas co-processing with excipients works mainly by adding excipients that deflect moisture away from the active ingredients. Co-crystallization works by altering the crystal packing arrangements by introducing stabilizing co-formers. For hygroscopic pharmaceuticals, coating and co-crystallization are the most commonly employed strategies, whereas coating and encapsulation are popular for hygroscopic nutraceuticals (e.g., medicinal herbs, protein hydrolysates). Encapsulation is rarely applied on hygroscopic pharmaceuticals, just as co-crystallization is rarely used for hygroscopic nutraceuticals. Therefore, there is potential for improved hygroscopicity reduction by exploring beyond the traditionally used strategy.

Insightful vibrational imaging study on the hydration mechanism of carbamazepine

Anhydrous carbamazepine (CBZ) is an anti-convulsant drug commonly used to treat epilepsy and relieve trigeminal neuralgia. The presence of the dihydrate form in commercial CBZ tablets can change the dissolution rate of the active pharmaceutical ingredient (API), thus decreasing its activity. The hydration transformation can occur during wet granulation or storage, within a few weeks, depending on the ambient conditions. This work aims to investigate the effect of relative humidity (RH) in the transition of pure anhydrous CBZ (CBZ III) into the hydrate form by using confocal Raman microscopy with cluster analysis (CA). Firstly, several tablets of pure CBZ III containing different amounts of CBZ DH (50%, 10%, 1%, 0.5%) were prepared and analyzed by Raman imaging with CA. Our results show that CBZ DH crystals can be detected in the CBZ III tablets, at as low a concentration as 0.5%, giving distinct Raman features for the analysed polymorphs. The stability of pure anhydrous (CBZ III) tablets was then monitored by Raman imaging at room temperature (20-22 °C) and different RH (6%, 60% and 89%). The Raman imaging with CA showed that the anhydrous CBZ tablets start to convert into the hydrate form after 48 h, and it completely changes after 120 hours (5 days) at RH 89%. The tablets exposed to RH 6% and 60% did not demonstrate the presence of CBZ DH after 1 week of exposure. The exposure time was extended for 9 months in the former, and no CBZ DH was observed. A comparative study using IR imaging was also performed, demonstrating the viability of these vibrational imaging techniques as valuable tools to monitor the hydration process of active pharmaceutical ingredients.

Structural and Reactivity Analyses of Nitrofurantoin–4-dimethylaminopyridine Salt Using Spectroscopic and Density Functional Theory Calculations

Pharmaceutical salt, nitrofurantoin–4-dimethylaminopyridine (NF-DMAP), along with its native components NF and DMAP are scrutinized by FT-IR and FT-Raman spectroscopy along with density functional theory so that an insight into the H-bond patterns in the respective crystalline lattices can be gained. Two different functionals, B3LYP and wB97X-D, have been used to compare the theoretical results. The FT-IR spectra obtained for NF-DMAP and NF clearly validate the presence of C33–H34⋅⋅⋅O4 and N23–H24⋅⋅⋅N9 hydrogen bonds by shifting in the stretching vibration of –NH and –CH group of DMAP+ towards the lower wavenumber side. To explore the significance of hydrogen bonding, quantum theory of atoms in molecules (QTAIM) has been employed, and the findings suggest that the N23–H24⋅⋅⋅N9 bond is a strong intermolecular hydrogen bond. The decrement in the HOMO-LUMO gap, which is calculated from NF → NF-DMAP, reveals that the active pharmaceutical ingredient is chemically less reactive compared to the salt. The electrophilicity index (ω) profiles for NF and DMAP confirms that NF is acting as electron acceptor while DMAP acts as electron donor. The reactive sites of the salt are plotted by molecular electrostatic potential (MEP) surface and calculated using local reactivity descriptors.

Spectroscopic (FT-IR, FT-Raman, and 13C SS-NMR) and quantum chemical investigations to provide structural insights into nitrofurantoin–4-hydroxybenzoic acid cocrystals

Non-covalent interactions contribute considerably to the stability of cocrystals and have appreciable effects on their molecular geometry as well.

Study of molecular interactions and chemical reactivity of the nitrofurantoin–3-aminobenzoic acid cocrystal using quantum chemical and spectroscopic (IR, Raman, 13C SS-NMR) approaches

Inquiries of structural reactivity, molecular interactions and vibrational characterization of drugs are essential in understanding their behaviour.

Polymorphism in anti-hyperammonemic agent N-carbamoyl-l-glutamic acid

Solid form screen of anti-hyperammonemic drug carglumic acid (CGA) resulted in two polymorphs, Form-I and Form-II. The crystal structure of Form-I is sustained by an acid catemer synthon, whereas Form-II has an acid–amide heterosynthon. Slurry grinding, thermal stress, stability measurements, and DVS analysis confirm the thermodynamic stability of Form-I.

Nitro-furan-toin methanol monosolvate

The anti-biotic nitro-furan-toin {systematic name: (E)-1-[(5-nitro-2-fur-yl)methyl-idene-amino]-imidazolidine-2,4-dione} crys-tallizes as a methanol monosolvate, C(8)H(6)N(4)O(5)·CH(4)O. The nitro-furan-toin mol-ecule adopts a nearly planar conformation (r.m.s. deviation = 0.0344 Å). Hydrogen bonds involve the co-operative N-H⋯O-H⋯O heterosynthons between the cyclic imide of nitro-furan-toin and methanol O-H groups. There are also C-H⋯O hydrogen bonds involving the nitro-furan-toin mol-ecules which support the key hydrogen-bonding synthon. The overall crystal packing is further assisted by weak C-H⋯O inter-actions, giving a herringbone pattern.

Effect of spectroscopic properties on photostability of tamoxifen citrate polymorphs

The photostability of tamoxifen citrate polymorphs, forms A and B, was investigated by chromatographic and spectroscopic analyses including high-pressure liquid chromatography (HPLC), colorimetry and UV/vis solid-state absorption spectroscopy. On the basis of the results of photostability studies under irradiation by visible light and both UVA (320-400 nm) and a fraction of UVB (290-320 nm) light, form A was chemically unstable, whereas form B was stable against light irradiation. The surface color of pellets prepared with any of these crystal forms turned from white to brown; however, the extent of color change in cross-sections of form A pellet was deeper than that of form B pellet. The maximum peak of UV/vis solid-state absorption spectra of form A was observed at 337 nm within the UVA range and was in longer wavelength regions than form B, which exhibited the strong UV absorption mainly in UVB and UVC region. The results obtained suggested that the photodegradation followed by surface color change of form A crystal was caused by the selective absorption of photoenergy of UVA light irradiated by a xenon lamp.

Physicochemical Characterization of Tamoxifen Citrate Pseudopolymorphs, Methanolate and Ethanolate

Two novel pseudopolymorphs, methanolate and ethanolate of tamoxifen [(Z)-2-[4-(1,2-diphenyl-1-butenyl)phenoxy]-N,N-dimethylethylamine]citrate, were prepared in addition to forms A and B reported previously. Their crystalline forms were identified and characterized by powder and single crystal X-ray diffractometry, differential scanning calorimetry, thermogravimetric analysis, hot-stage microscopy, scanning electron microscopy and diffuse reflectance infrared Fourier-transform spectroscopy, and their physicochemical stability was also evaluated. The results of single crystal X-ray analysis and thermogravimetric analysis of methanolate and ethanolate suggested that the stoichiometry of tamoxifen citrate : methanol and tamoxifen citrate : ethanol could be composed of a 1 : 1 molecular ratio for both solvates. The results of physicochemical stability evaluations at 75 and 97% RH at 40 and 60 degrees C indicated that the metastable form A was quite stable for at least 2 months even under severe storage conditions, whereas methanolate immediately transformed to a crystalline mixture of forms A and B, and subsequently changed to the stable form B.

Pellet manufacturing by extrusion-spheronization using process analytical technology

The aim of this study was to investigate the phase transitions occurring in nitrofurantoin and theophylline formulations during pelletization by extrusion-spheronization. An at-line process analytical technology (PAT) approach was used to increase the understanding of the solid-state behavior of the active pharmaceutical ingredients (APIs) during pelletization. Raman spectroscopy, near-infrared (NIR) spectroscopy, and X-ray powder diffraction (XRPD) were used in the characterization of polymorphic changes during the process. Samples were collected at the end of each processing stage (blending, granulation, extrusion, spheronization, and drying). Batches were dried at 3 temperature levels (60 degrees C, 100 degrees C, and 135 degrees C). Water induced a hydrate formation in both model formulations during processing. NIR spectroscopy gave valuable real-time data about the state of water in the system, but it was not able to detect the hydrate formation in the theophylline and nitrofurantoin formulations during the granulation, extrusion, and spheronization stages because of the saturation of the water signal. Raman and XRPD measurement results confirmed the expected pseudopolymorphic changes of the APIs in the wet process stages. The relatively low level of Raman signal with the theophylline formulation complicated the interpretation. The drying temperature had a significant effect on dehydration. For a channel hydrate (theophylline), dehydration occurred at lower drying temperatures. In the case of isolated site hydrate (nitrofurantoin), dehydration was observed at higher temperatures. To reach an understanding of the process and to find the critical process parameters, the use of complementary analytical techniques are absolutely necessary when signals from APIs and different excipients overlap each other.

The use of dynamic vapour sorption and near infra-red spectroscopy (DVS-NIR) to study the crystal transitions of theophylline and the report of a new solid-state transition

This study was undertaken to see if the combined technique of DVS-NIR could add to the understanding of transitions between physical forms of theophylline. There was excellent correlation between the mass changes and the intensity of the NIR peaks, showing that the hydrate was being formed and lost. This was characterised by the peaks at 1478 and 1972 nm representing an -OH deformation. NIR spectra for desorption shows that the dehydrate retains partial structure of both the anhydrate and hydrate crystal lattices. During rehydration of the dehydrate a new transition was discovered. An unexpected mass loss occurred between 40 and 50% RH. Usually, a mass loss during water sorption is characteristic of crystallisation of an amorphous material, although in this case it could be that the sample is crystalline. NIR data showed that during this transition the dehydrate peaks reverted back to the peak positions seen for anhydrous theophylline. The absorption of water into the dehydrate allowed the freedom of movement for the stable anhydrous lattice to form. It was concluded that DVS-NIR is a useful tool to study solid-state transitions and that the transition exists for conversion of theophylline dehydrate to anhydrate which is facilitated through water sorption.

Physicochemical characterization of glybuzole polymorphs and their pharmaceutical properties

Systematic polymorphic screening tests were performed using 11 kinds of solvents and 6 kinds of preparation methods, and the three specific modifications of glybuzole (forms I and II and amorphous form) were identified by X-ray diffractometry and differential thermal analysis (DTA). The physicochemical properties of forms I and II and amorphous forms were measured using X-ray diffractometry, differential scanning calorimetry (DSC), thermogravimetry (TG), scanning electron microscopy (SEM), solubility tests, and others. The solubilities of all modifications in JP XII, first and second fluid (pH 1.2 and 6.8, respectively) were evaluated at 37 degrees C. Forms I and II and the amorphous form showed almost equivalent solubilities. Forms I and II were stable polymorphic forms at 0% and 75% relative humidity (RH), respectively, at 40 degrees C for 2 months, but the amorphous form was not stable. The crystallization rates of the amorphous form at 0% and 75% RH at 40 degrees C were estimated by X-ray diffraction analysis based on the Jander equation, and the rate at 0% RH was 364 times slower than that at 75% RH.