Accessing Mefenamic Acid Form II through High-Pressure Recrystallisation

An Additive Manufacturing MicroFactory: Overcoming Brittle Material Failure and Improving Product Performance through Tablet Micro-Structure Control for an Immediate Release Dose Form

Additive manufacturing of pharmaceutical formulations offers advanced micro-structure control of oral solid dose (OSD) forms targeting not only customised dosing of an active pharmaceutical ingredient (API) but also custom-made drug release profiles. Traditionally, material extrusion 3D printing manufacturing was performed in a two-step manufacturing process via an intermediate feedstock filament. This process was often limited in the material space due to unsuitable (brittle) material properties, which required additional time to develop complex formulations to overcome. The objective of this study was to develop an additive manufacturing MicroFactory process to produce an immediate release (IR) OSD form containing 250 mg of mefenamic acid (MFA) with consistent drug release. In this study, we present a single-step additive manufacturing process employing a novel, filament-free melt extrusion 3D printer, the MicroFactory, to successfully print a previously 'non-printable' brittle Soluplus®-based formulation of MFA, resulting in targeted IR dissolution profiles. The physico-chemical properties of 3D printed MFA-Soluplus®-D-sorbitol formulation was characterised by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), and X-ray Diffraction Powder (XRPD) analysis, confirming the crystalline state of mefenamic acid as polymorphic form I. Oscillatory temperature and frequency rheology sweeps were related to the processability of the formulation in the MicroFactory. 3D printed, micro-structure controlled, OSDs showed good uniformity of mass and content and exhibited an IR profile with good consistency. Fitting a mathematical model to the dissolution data correlated rate parameters and release exponents with tablet porosity. This study illustrates how additive manufacturing via melt extrusion using this MicroFactory not only streamlines the manufacturing process (one-step vs. two-step) but also enables the processing of (brittle) pharmaceutical immediate-release polymers/polymer formulations, improving and facilitating targeted in vitro drug dissolution profiles.

Exploring the effects of high pressure on hydrogen bonding in pharmaceutical cocrystals: A systematic study of pyridine dicarboxylic acid systems using synchrotron and neutron diffraction

Pharmaceutical cocrystals use common robust hydrogen bonding synthons to create novel materials with different physicochemical properties. In this systematic study of a series of cocrystals, we explore the effect of high pressure on one of these commonly used motifs, the acid-pyridine motif, to assess the commonality of behaviour under extreme conditions. We have surveyed five pyridine dicarboxylic acid systems using both synchrotron and neutron diffraction methods to elucidate the changes in structure. We observe that the hydrogen bonding in these systems compress at a similar rate despite the changes to the molecular make-up of the solids and that on compression the changes in structure are indicative that the layers move along the major slip planes in the structure. We have observed two phase transitions to new forms of the pyrazine:malonic acid system, one for each stoichiometric ratio. This study demonstrates that the combination of two complementary diffraction approaches is key to understanding polymorphic behaviour at high pressure.

Molecular Mechanism of Conformational Crossover of Mefenamic Acid Molecules in scCO2

In this work, we studied conformational equilibria of molecules of mefenamic acid in its diluted solution in scCO₂ under isochoric heating conditions in the temperature range of 140-210 °C along the isochore corresponding to the scCO₂ density of 1.1 of its critical value. This phase diagram range totally covers the region of conformational transitions of molecules of mefenamic acid in its saturated solution in scCO₂. We found that in the considered phase diagram region, the equilibrium of two conformers is realized in this solution. In the temperature range of 140-180 °C, conformer I related to the first, most stable polymorph of mefenamic acid prevails. In the temperature range of 200-210 °C, conformer II, which is related to the second metastable polymorph becomes dominant. Based on the results of quantum chemical calculations and experimental IR spectroscopy data on the mefenamic acid conformer populations, we classified this temperature-induced conformational crossover as an entropy-driven phenomenon.

The Role of Hidden Conformers in Determination of Conformational Preferences of Mefenamic Acid by NOESY Spectroscopy

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters.

Quantum Chemical Study on Mefenamic Acid Polymorphic Forms

Three polymorphic structures of mefenamic acid, which is a very popular drug, have been studied using quantum chemical methods. It has been shown that the centrosymmetric dimer formed due to two O-H···O hydrogen bonds is a complex building unit in all of the polymorphic structures under study. On the basis of an analysis of the pairwise interaction energies between molecules, the polymorphic forms I and II are classified as columnar-layered while the polymorphic form III has a columnar structure. The stabilities of the three polymorphic forms of mefenamic acid under ambient conditions (I > II > III) correlate with the degree of anisotropy of the interaction energies between columns (primary basic structural motifs) formed due to stacking interactions. The shear deformation modeling of strongly bound layers in all of the polymorphic structures has not revealed any possibility for deformation of the crystal structure. The construction of the shift energy profiles and calculation of the energy barriers for the displacement along the (100) crystallographic plane in the [100], [010], and [011] crystallographic directions make it possible to explain the experimental data obtained for commercially available polymorphic structure I in a diamond anvil cell. The absence of any local minimum near the starting point on the shift energy profile and the extremely high energy barrier can be considered as criteria for the impossibility of a crystal structure deformation under pressure.

Mefenamic acid solid dispersions: Impact of formulation composition on processing parameters, product properties and performance

The objective of this study was to develop an immediate release (IR), crystalline solid dispersion (CSD) formulation of Mefenamic acid (MFA) by hot-melt-extrusion (HME) and assess the impact of drug loading on process parameters, product physico-chemical properties and product performance. An HME process to produce a range of MFA-Soluplus®-Sorbitol polymer matrix CSD formulations was developed based on rheological screening assays of physical mixtures (PM). The impact of drug loading on process parameters was compared to the impact of drug loading on the physico-chemical properties of formulations. Based on process and product data, three groupings of API drug loading were identified: sub-saturated, saturated, and supersaturated systems. CSD formulations were obtained for 20 - 50% (w/w) drug loading containing the stable polymorphic form I of MFA. CSD formulations predominantly improved the consistency of the product performance. An Amorphous Solid Dispersion (ASD) was obtained for 10% (w/w) drug loading, exhibiting faster drug release even at physiologically relevant pH. This study illustrates the impact of drug loading on process and product characteristics and how a better understanding of maximum API solubility in a given polymer system can improve targeted formulation development.

Improving Consistency for a Mefenamic Acid Immediate Release Formulation

The objective of this study was to develop an immediate release dose form containing 250 mg Mefenamic acid (MFA) presented as a crystalline solid dispersion in order to achieve improved consistency in drug release through a simplified formulation compared to a commercial product. An MFA-Soluplus®-Sorbitol polymer matrix was developed using an HME process based on rheological screening assays of physical mixtures. The physico-chemical properties of these formulations were assessed by thermal analysis, FTIR, mechanical testing and SEM image analysis, confirming the crystalline character and stable polymorphic form I of the API in the polymer matrix. A faster release and a significant improvement in consistency (±6%) of drug release was observed compared to a commercially available MFA product (±17%) (250 mg capsule). This study illustrates advantages of applying a structured development program aimed at retaining API physical properties in the final dosage form.

Quasi-Isostructural Co(II) and Ni(II) Complexes with Mefenamato Ligand: Synthesis, Characterization, and Biological Activity

Three metal complexes of mefenamato ligand 1 were synthesized: [Co2(mef)4(EtOH)2(H2O)4]: 2; [Co(mef)2(MeOH)4]∙2MeOH: 3; and [Ni(mef)2(MeOH)4]∙2MeOH: 4. Their compositions and properties were investigated by elemental analysis (EA), flame atomic absorption spectrometry (FAAS), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Crystal structures were determined by the single crystal X-ray diffraction technique. Additionally, their antioxidant and antimicrobial activity were established, thus proving good/moderate bioactivity against Gram-positive bacteria and yeasts. In the crystal structure of 2, an apical water molecule is shared between two adjacent cobalt(II) ions, resulting in the formation of a polymeric chain extending along the [100] direction. Meanwhile, structures 3 and 4 have strong intermolecular hydrogen bonds with diverse topologies that yield unique quasi-isostructural arrangements. The packing topology is reflected by the Hirshfeld surface analysis of intermolecular contacts.

A simultaneous X-ray diffraction–differential scanning calorimetry study into the phase transitions of mefenamic acid

In this study, the polymorphic transitions of mefenamic acid (MA) were studied by synchrotron X-ray powder diffraction combined with differential scanning calorimetry (XRD-DSC). The initial material was found to be phase-pure form I which, when heated, produces two endotherms that can be observed by DSC at 162.72 and 219.55°C. The former was found to correspond to a solid–solid enantiotropic transition from form I to a mixture of forms II and III. The latter is the melting point of form II. As form I is heated, significantly greater unit-cell expansion is seen in the a direction than in b and c, which can be explained by the stronger intermolecular interactions in the bc plane. Refinements of the reported MA structures against the patterns collected during heating revealed that at 175°C there exists a mixture of forms I, II and III, whereas only forms II and III remain at 205°C. However, reflections are observed at both temperatures which cannot be fitted with the known forms of MA. It is hypothesized that a new form of MA is produced upon heating. The stability of MA after the enantiotropic transition temperature is II > III > I, which differs from the previously reported II > I > III.

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up to 5.0 GPa, the b axis compressing by 3.3%, and the a and c axes by 12.3 and 10.9 %. Since the chains are exactly aligned with the crystallographic b axis these data characterise the compressibility of the I···N interaction relative to the inter-chain interactions, and indicate that the halogen bond is the most robust intermolecular interaction in the structure, shortening from 3.168(4) at ambient pressure to 2.840(1) Å at 5.0 GPa. The π∙∙∙π contacts are most sensitive to pressure, and in one case the perpendicular stacking distance shortens from 3.6420(8) to 3.139(4) Å. Packing energy calculations (PIXEL) indicate that the π∙∙∙π interactions have been distorted into a destabilising region of their potentials at 5.0 GPa. The structure undergoes a transition to a triclinic ( P 1 ¯ ) phase at 5.5 GPa. Over the course of the transition, the initially colourless and transparent crystal darkens on account of formation of microscopic cracks. The resistance drops by 10% and the optical transmittance drops by almost two orders of magnitude. The I···N bond increases in length to 2.928(10) Å and become less linear [<C-I∙∙∙N = 166.2(5)°]; the energy stabilises by 2.5 kJ mol^-1 and the mixed C-I/I..N stretching frequency observed by Raman spectroscopy increases from 249 to 252 cm^-1. The driving force of the transition is shown to be relief of strain built-up in the π∙∙∙π interactions rather than minimisation of the molar volume. The triclinic phase persists up to 8.1 GPa.

Discovery and recovery of delta p-aminobenzoic acid

A new high-pressure recoverable form has been observed in the model system, p-aminobenzoic acid.