Investigations on solid-solid phase transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile.

Solid-solid transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile from the dark-red to the red form was investigated. By controlled crystallization, the dark-red form was prepared and the crystals were sieved into fractions: coarse (>250 microm), medium (125-177 microm), and fine (<88 microm). The transformation rate order (fastest to slowest) of the different fractions is coarse > medium > fine. However, milling accelerates the transformation, that is, smaller particles generated by milling transforms faster. Furthermore, ethanol vapor annealing slows both the transformation of the coarse and medium fractions, especially the latter. Therefore, the mechanism of transformation is not directly related to the crystal-size and most likely related to the amount and activity of the defects in the crystals. The three-dimensional (3-D) Avrami-Erofe'ev model, know as "random nucleation and growth" model, fits the kinetics of coarse fraction best. Higher relative humidity accelerates the transformation dramatically even though the compound is highly-hydrophobic. With minimal hydrogen bonding interaction involved, it appears even small amounts of water can serve as a nucleation catalyst by binding to the crystal surface, especially at defect sites, thus increasing the molecular mobility of these sites, promoting the transformation to the second phase and thereby increasing the transformation rate.

PQRI recommendations on particle-size analysis of drug substances used in oral dosage forms.

This document provides information for the Pharmaceutical Industry and the Federal Drug Administration (FDA) regarding the selection of suitable particle-size analysis techniques, development and validation of particle-size methods, and the establishment of acceptance criteria for the particle size of drug substances used in oral solid-dosage forms. The document is intended for analysts knowledgeable in the techniques necessary to conduct particle-size characterization (a table of acronyms is provided at the end of the document). It is acknowledged that each drug substance, formulation, and manufacturing process is unique and that multiple techniques and instruments are available to the analyst.

Effect of milling and compression on the solid-state Maillard reaction.

The effects of milling and compression on the solid-state Maillard reaction between metoclopramide hydrochloride and lactose were investigated. Anhydrous metoclopramide hydrochloride was milled for various times, and then mixed with amorphous lactose. The mixtures were stored at 105 degrees C and 0% RH. The reactivity of metoclopramide hydrochloride towards the Maillard reaction increased with milling time, as the result of increased surface area, formation of amorphous content, and creation of defects. Metoclopramide hydrochloride anhydrate and lactose were mixed and the mixtures were compressed into tablets under pressure varied from 70 to 350 MPa. Both tablets and mixtures were stored at 105 degrees C and 0% RH for 9 days. For all three types of lactose used, spray-dried anhydrous lactose, spray-dried lactose monohydrate, and amorphous lactose, tablets exhibited higher reaction rate toward the Maillard reaction than the powder mixtures. Tablets containing metoclopramide hydrochloride and amorphous lactose prepared at higher pressure showed higher reaction rates than those prepared at lower pressure. This is due to increased contact between reactants and an increased amount of water retained in the tablets.

Kinetic study of the Maillard reaction between metoclopramide hydrochloride and lactose.

The purpose of this work is to study the apparent solid-state kinetics of the Maillard reaction of the colyophilized metoclopramide hydrochloride (MCP) and lactose system and to elucidate some of the effects of molecular mobility on the kinetic behavior of the amorphous mixture. Colyophilized MCP-lactose mixtures (1:9 molar ratio) were stored at temperatures ranging from 100 to 115 degrees C (above the glass transition temperature, Tg=99.7 degrees C). This temperature range, which corresponds to the change between the glass and liquid states of the lactose-MCP mixtures, is also the temperature region where molecular mobility represents a kinetic impediment of enough significance as to affect the observed order of the reaction. A pseudo second-order kinetic model was developed to fit the MCP loss data. The proposed model gives better fit to the degradation data than many of the commonly used kinetic models available in the literature. The second-order rate constant of the model follows Arrhenius kinetics and the activation energy was found to be 53.8 kcal mol(-1). The molecular mobility (relaxation time) of the mixture was calculated from the heating rate dependence of the DSC-determined glass transition temperature of the mixtures. From molecular mobility considerations alone, it is possible to accurately predict the temperature dependence of the reaction rate constant. These results support the hypothesis that the solid-state reaction is mobility controlled.

Analysis of the acid-base reaction between solid indomethacin and sodium bicarbonate using infrared spectroscopy, X-ray powder diffraction, and solid-state nuclear magnetic resonance spectroscopy.

Indomethacin was used as a model compound to investigate acid-base reactions of solid materials, a common type of drug-excipient interaction. In a typical experiment, 500 mg of pure alpha-form indomethacin were mixed with 500 mg of sodium bicarbonate. The mixture was kept at 40 degrees C and at several relative humidities. The reaction was monitored by IR spectroscopy, X-ray powder diffraction, and solid-state NMR. At 40 degrees C and 80% RH, the reaction is nearly complete after 300 h. As observed by IR spectroscopy, the characteristic peaks of alpha-indomethacin disappear during the course of the reaction with the appearance of the characteristic peaks of the salt product, sodium indomethacin trihydrate. Solid-state NMR spectra and X-ray powder diffraction patterns of the reaction mixtures confirm the transformation of the mixtures to sodium indomethacin trihydrate; the reduced peak intensities in the diffraction patterns of the product relative to the initial mixtures indicate the formation of a microcrystalline product. A change in the reaction rate of sodium bicarbonate with alpha-indomethacin is observed when the mixtures are stored at different relative humidities. At 40 degrees C and 66% RH, the reaction of sodium bicarbonate with alpha-indomethacin is about 86% complete after 500 h. No detectable reaction was observed for sodium bicarbonate with the alpha form of indomethacin at 40 degrees C and 11% RH after 15 months. The combination of these solid-state characterization techniques is demonstrated to be essential to detect and monitor acid-base reactions in solid materials, which are impossible to monitor using solution-chemistry methods. The reaction kinetics at 66% RH fits the Jander equation very well, which is consistent with a diffusion-controlled mechanism.

Monoprotic Tetradentate N(3)O-Donor Ligands and Their Cu(II) and Ni(II) Complexes.

A convenient four-step procedure was developed to prepare the novel monoprotic tetradentate ligands N-(2-hydroxy)benzyl-N-methyl-N'-(2-pyridyl)methyl-1,3-propanediamine (Hpamap) and N-(2-hydroxy)benzyl-N'-methyl-N'-(2-pyridyl)methyl-1,3-propanediamine (Hpmaap), which provide an N(3)O metal coordination sphere. A mononuclear copper(II) complex, [Cu(pamap)Cl] (A), was obtained by reaction of Hpamap with CuCl(2).2H(2)O. The binuclear copper(II) complexes [Cu(pamap)](2)(BF(4))(2) (B) and [Cu(pmaap)](2)(BF(4))(2) (C) were obtained when these ligands were reacted with Cu(II) in the presence of the noncoordinating BF(4)(-) anion. Reaction of nickel(II) with the Hpamap ligand generated the binuclear Ni(II) complex [Ni(2)(pamap)(2)(NO(3))]NO(3) (D). The crystal of A (C(17)H(22)ClCuN(3)O) is orthorhombic Pbca (No. 61), a = 11.837(4) Å, b = 15.648(5) Å, c = 11.002(11) Å, Z = 8; that of B (C(34)H(44)B(2)Cu(2)F(8)N(6)O(2)) is triclinic P&onemacr; (No. 2), a = 9.147(0) Å, b = 10.375(0) Å, c = 10.535(1) Å, alpha = 107.20(0) degrees, beta = 91.19(0) degrees, gamma = 105.05(0) degrees, Z = 1; that of C (C(34)H(44)B(2)Cu(2)F(8)N(6)O(2)) is monoclinic P2(1)/c (No. 14), a = 9.158(2) Å, b = 10.714(2) Å, c = 19.085(4) Å, beta = 90.58(2) degrees, Z = 4; and that of D (C(34)H(44)N(8)NiO(8)) is monoclinic C2/c (No. 15), a = 13.849(0) Å, b = 13.609(0) Å, c = 19.558(1) Å, beta = 92.34 (0) degrees, Z = 4. The copper atoms of all three complexes are five-coordinate in the solid state, assuming the geometry of a distorted square pyramid with the deprotonated tetradentate ligand in the basal plane. The mononuclear complex A has a chloride ligand in the axial position, while each copper center in the binuclear complexes B and C has, in the axial position, a bridging phenolate O donor from the other unit of the dimer. Each nickel center in the binuclear complex D is six-coordinate, with the pseudo-octahedron formed by a deprotonated tetradentate ligand, a bridging nitrato oxygen atom, and a bridging phenoxy donor from the tetradentate ligand bound to the second nickel center.

Quantitative study of solid-state acid-base reactions between polymorphs of flufenamic acid and magnesium oxide using X-ray powder diffraction.

The purpose of this study is to investigate solid-state acid-base reactions between polymorphs of flufenamic acid (FFA) and magnesium oxide (MgO) using X-ray powder diffraction (XRPD). Polymorphs of FFA were blended with MgO and stored under conditions of 96.5% RH and 89% RH at 40 degrees C. The disappearance of FFA and production of magnesium flufenamate were monitored by XRPD. It was observed that the reactions between FFA and MgO proceeded following the Jander equation. Form I of FFA is more reactive with MgO than Form III. Differential accessibility of reactive groups is hypothesized as one of the reasons that Form I is more reactive than Form III. It was noted that the reaction between FFA and MgO could be mitigated by adding another acidic excipient such as polyacrylic acid to prevent the acid-base reaction with FFA. The effectiveness of polyacrylic acid was impacted by the mixing order of the tertiary mixture. Mixing polyacrylic acid and MgO first provided the most significant protection. In conclusion, solid-state acid-base reactions could be investigated using XRPD. Different forms may have distinct reactivity. Acid-base reactions in the solid state could be mitigated through the addition of another "shielding" excipient.

Crystal quality and physical reactivity in the case of flufenamic acid (FFA).

In reality, no crystal is perfect. Crystals bear defects both in the bulk and on the surface. The purpose of this project is to study the correlation between crystal defect density and reactivity of physical transformation. The hypothesis is that larger crystals have the opportunity to pick up more defects during crystal growth than smaller crystals, therefore, have higher reactivity. Flufenamic acid (FFA) was used as a model compound. Phase transformation of crystal Form I (white) to Form III (yellow) of FFA was studied, and observed that larger crystals of FFA Form I transform faster. Furthermore, the etching pits identified on the major crystal faces (1 0 0) using atomic form microscopy (AFM) also showed that larger crystals had higher surface defect density than smaller ones, which correlates with the finding that larger crystals transforms faster than smaller ones.

Reactivity differences of indomethacin solid forms with ammonia gas.

The present study deals with the acid-base reaction of three solid-state forms of the nonsteroidal antiinflammatory drug indomethacin with ammonia gas. X-ray powder diffraction, optical microscopy, gravimetry, and spectroscopic methods were employed to establish the extent of the reaction as well as the lattice changes of the crystal forms. The glassy amorphous form readily reacts with ammonia gas to yield a corresponding amorphous ammonium salt. In addition, the metastable crystal form of indomethacin (the alpha-form) also reacts with ammonia gas, but produces the corresponding microcrystalline ammonium salt. This reaction is anisotropic and propagates along the a-axis of the crystals. The stable crystal form (the gamma-form), however, is inert to ammonia gas. Amorphous indomethacin can react with ammonia gas because it has more molecular mobility and free volume. The reactivity differences between the alpha- and gamma-forms are dictated by the arrangement of the molecules within the respective crystal lattices. The recently determined crystal structure of the metastable alpha-form of indomethacin (monoclinic P2(1) with Z = 6, V = 2501.8 A(3), D(c) = 1.42 g.cm(-3)) has three molecules of indomethacin in the asymmetric unit. Two molecules form a mutually hydrogen-bonded carboxylic acid dimer, while the carboxylic acid of the third molecule is hydrogen bonded to one of the amide carbonyls of the dimer. The carboxylic acid groups of the alpha-form are exposed on the [100] faces and are accessible to attack by ammonia gas. After one layer of molecules reacts, the reactive groups in the subsequent layer are accessible to the ammonia gas. This process proceeds along the a-axis until the ammonia gas has penetrated the entire crystal. In contrast to the alpha-form, the gamma-form has a centrosymmetric crystal structure in which the hydrogen-bonded carboxylic acid dimers are not accessible to ammonia gas because they are caged inside a hydrophobic shield comprising the remainder of the indomethacin molecule. In view of the significantly lower density of the stable gamma-form as compared to the metastable alpha-form (1.37 and 1.42 g cm(-3), respectively), it became apparent that the reactivity of the crystal forms depends exclusively on the molecular arrangement and not on the packing density of the indomethacin crystals.

Modeling and monitoring of polymorphic transformations during the drying phase of wet granulation.

PURPOSE: The purpose of this work was to monitor polymorphic transformations of glycine during the drying phase of a wet granulation and model the polymorphic conversions using a time-based reconciliation model. METHODS: Near-infrared spectroscopy (NIR) was used for quantitation of polymorphs, and X-ray powder diffraction (XRPD) was used for qualitative analysis of polymorphs. RESULTS: The data show that the faster the granulation was dried, the more kinetic trapping of the metastable alpha-glycine polymorph, as predicted by reconciliation of the time scales of both the drying rate and the rate of the solution-mediated conversion. CONCLUSIONS: By knowing basic properties of the drug substance (solubility of the polymorphic forms and the rate of the solution-mediated conversion), processing conditions, such as the drying rate, can be adjusted to anticipate and prevent potential polymorphic transformations.

In situ monitoring of wet granulation using online X-ray powder diffraction.

PURPOSE: Polymorphic transformations during the wet granulation of a metastable polymorph of flufenamic acid were monitored in situ using online X-ray powder diffraction. The resulting data were used in testing a proposed process induced transformation rate model, which allows the extent and occurrence of polymorphic transformations during wet granulation to be controlled by adjusting the granulation time. METHODS: A small-scale, top mixing granulator was designed for compatibility with novel X-ray powder diffraction equipment (available from X-Ray Optical Systems of East Greenbush, NY). RESULTS: The unique polycapillary optic and X-ray source allowed the transformation of the metastable to the stable polymorph to be followed during the granulation. Following a diffraction peak each for the metastable and stable forms demonstrated that polymorphic transformations during the wetting phase of granulation follow the trends predicted by the model. CONCLUSIONS: The advanced online monitoring may allow real-time control of the process by the adjustment of process parameters, such as granulation time, and clearly qualifies as a PAT (process analytical technology).