Characterization and Selective Crystallization of Famotidine Polymorphs

Optimization of the stability constants of the ternary system of diclofenac/famotidine/β-cyclodextrin by nonlinear least-squares method using theoretical equations

This study aimed to establish a new method for determining the stability constants of drug/β-cyclodextrin (β-CD) complexes when multiple drugs interacting with each other coexist in the solution of complexation. The basic drug famotidine (FAM) and the acidic drug diclofenac (DIC) were used as model drugs, their solubility decreasing owing to their mutual interaction. The dissolution of both FAM and DIC was characterized by A_L-type phase solubility diagrams in the presence of the other's 1:1 complex with β-CD. When the stability constant was calculated from the slope of the phase solubility diagram using the conventional phase solubility diagram method, it was modified in the presence of the other drug. However, by performing optimization calculations that considered the interactions between the drug/β-CD complex and the drug, drug/β-CD complexes, and drugs, we were able to accurately calculate the stability constant of DIC/β-CD and FAM/β-CD complexes even in the presence of FAM and DIC, respectively. The results of the solubility profile indicated that various molecular species, which are attributed to drug-drug and drug/β-CD interactions, interfere with the values of the dissolution rate constants and saturated concentration in the solubility profiles.

Analysis of Cimetidine Crystal Polymorphs by X-ray Absorption Near-Edge Spectroscopy

Sulfur K-edge X-ray absorption near-edge spectroscopy (XANES) measurements were performed to characterize the crystal polymorphs of the active pharmaceutical ingredients (APIs) containing sulfur atoms. Cimetidine (CIM) was used as a model API. Each crystal form of CIM has its own XANES spectrum, so we can discriminate the crystal form by its spectrum. The analysis of the crystal structure of CIM revealed that the difference in the shape of XANES spectra was ascribable to the difference in the C-S-C bond angle of CIM molecules and the intermolecular hydrogen bonds, such as C-H···S and N-H···S, and S-S interaction. It was found that the peak shape of the XANES spectrum is gentle when the C-S-C bond angle is large, while the peak shape can be steep when the C-S-C bond angle is small. Furthermore, it was found that the peak energy values varied depending on the hydrogen bonds and S-S interaction. By linear combination fitting using XANES spectra, it was possible to quantify the ratio of CIM form A crystal in mixed powders of form A and monohydrate crystals. These results indicate that XANES measurements can be a useful technique to evaluate the crystal polymorphism of APIs containing S atom in pharmaceutical formulation.

Characterization and Crystal Nucleation Kinetics of a New Metastable Polymorph of Piracetam in Alcoholic Solvents

A new polymorph of the drug active pharmaceutical ingredient piracetam (Form VI) has been discovered and characterized by X-ray powder diffraction (PXRD), solid-state Raman, attenuated total reflectance infrared spectroscopy, and differential scanning calorimetry. The PXRD diffractogram of Form VI shows a distinct peak at 24.2° (2θ) that distinguishes it from the previously known polymorphs and solvates. Form VI is metastable with respect to the previously known polymorphs Form II and Form III; in ethanol solution at 288 K, Form VI transforms into Form II within 15 min, while in isopropanol solution Form VI is kinetically stable for at least 6 h. A total of 1200 crystal nucleation induction time experiments of piracetam in ethanol and isopropanol solutions have been conducted, in sets of 40-80 repeat experiments carried out at different temperatures and solute concentrations. Each solution nucleated as a single polymorph, and each set of repeat experiments resulted in different proportions of Form II, Form III, and Form VI, with Form VI dominating at low nucleation temperatures and Form II at higher nucleation temperatures. The induction time data for Form VI at 288 K have been evaluated within the framework of the classical nucleation theory. At equal driving force, nucleation of Form VI is less obstructed in ethanol than in isopropanol, as captured by a lower interfacial energy and higher pre-exponential factor in ethanol. The proportion of Form VI obtained at a comparable driving force increases in the order ethanol < isopropanol.

Polymorphs of DP-VPA Solid Solutions and Their Physicochemical Properties

Different solid forms possess various physicochemical properties, which can significantly affect the stability, bioavailability, and manufacturability of the final product. DP-VPA, a complex of 1-stearoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₈) and 1-palmitoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₆), is currently under development as an antiepileptic drug. DP-VPA-C₁₆ and DP-VPA-C₁₈ crystallize together in solid solution forms. The solid forms of DP-VPA solid solution were studied herein. Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), dynamic vapor sorption (DVS) and optical microscopy were used to characterize the different crystalline forms, known as polymorphs. The physicochemical properties, including hygroscopicity, thermodynamic behavior, and relative stability, of each form were investigated. DVS analysis showed that DP-VPA solid solution reduced the hygroscopicity of DP-VPA-C₁₆. The relative humidity stability study revealed that Forms A and B are relatively stable, while Forms A-1, B-1, C and D are highly unstable under natural humidity. Further analysis revealed that Form A transforms into Form B through milling. Given the physicochemical properties of the available physical forms, Form B may be the optimal form for the formulation and development of antiepileptic drugs.

The physical stability of drugs linked to quality-by-design (QbD) and in-process technology (PAT) perspectives

The physical stability of solid-state forms in which drugs may exist is in some sense an overlooked aspect. In an era where strategies such as amorphous solid dispersions or co-amorphous preparations might provide answers to stumbling blocks such as poor drug solubility and bioavailability, the physical stability of such solid-state preparations should be a priority. Furthermore, the pharmaceutical industry is moving towards adapting a real time release of pharmaceutical products strategy, through the utilization of process analytical technology. It is thus becoming imperative to investigate the various types of phase transformations a specific solid-state form of a drug may undergo. Also, to critically assess the applicability of process analytical tools that may be sensitive enough to monitor not only chemical but also physical drug stability. These combined efforts allow quality to be built into the product, rather than dealing with costly post batch release recalls. Given that drug stability is an essential quality attribute for a drug product and the quality-by-design approach (QbD) is a best solution to build quality in all pharmaceutical products we focussed on the critical material attributes (CMAs), specifically relating to the physical stability of any given drug. This review highlights physical drug stability in relation to CMAs and how this ultimately link to the finished pharmaceutical product. Investigated challenges associated current PAT strategies is also discussed.

Concomitant polymorphs of methoxyflavone (5-methyl-7-methoxyflavone)

A novel metastable polymorph and an unstable amorphous phase of methoxyflavone were discovered after a decade since the first report of the X-ray crystal structure of this bioactive compound.