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PubMed2002

Effect of physicochemical and formulation variables on the in vivo absorption of ABT-761.

ABT-761 is a 5-lipoxygenase inhibitor developed for the treatment of asthma. The present study was undertaken to evaluate different crystal forms of ABT-761 and their impact on in vitro and in vivo performance in capsule formulations. Two crystal forms of ABT-761, hemihydrate and non-solvate from different sources, were characterized by thermal analysis, x-ray powder diffraction, moisture sorption, and intrinsic dissolution studies. An in vitro test was performed to assess the effect of formulation and drug from different sources on drug release. Crossover design was also used to evaluate oral bioavailability of ABT-761 hemihydrate formulations in beagle dogs. Plasma concentrations of ABT-761 were analyzed using a reverse-phase high-performance liquid chromatography (HPLC) assay. It was found that in vivo oral absorption as well as in vitro dissolution of ABT-761 were influenced by different formulations. Capsule formulations of ABT-761 hemihydrate are bioequivalent to the solution formulation in terms of extent of absorption, butformulation and the method of granulation preparation can have a major impact on the absorption rate. In conclusion, a single crystal form of ABT-761, i.e., hemihydrate, is preferred for subsequent product development. However, exposure of the drug to conditions that may facilitate phase transformation should be avoided.

Absorption↗
PubMed2002

The effect of ultrasonic vibration on the compaction characteristics of ibuprofen.

An ultrasonic (US) compaction rig has been developed, capable of providing compaction pressure together with high-power ultrasonic vibrations of 20 kHz to a powder or granular material in a die. The rig has been used to investigate the effect of ultrasound on the compaction properties of ibuprofen, a drug with poor compaction properties which produces tablets that are weak and frequently exhibit capping. It was found that coherent ibuprofen tablets could be prepared by ultrasound-assisted compaction at pressures as low as 20-30 MPa. Application of ultrasound before and after compaction was found not to be as effective as ultrasound applied during compaction. The breaking forces of the tablets produced with ultrasound applied during compaction were found to be consistently significantly higher than when compaction was performed conventionally, or with ultrasound applied before or after compaction. Application of ultrasound during compaction made it possible to increase tablet mechanical strength, typically by a factor of 2-5. It was concluded that pressure should be applied together with ultrasound in order to achieve a better acoustical contact, which is required to transmit vibrations from the horn to the material, and also to bond the surfaces of the particles. Ultrasound application during ibuprofen compaction also resulted in an increase in the apparent density, in relation to the apparent density of conventionally prepared tablets, of up to 14.4%. Ultrasound appears to improve particle rearrangement and provides energy for partial melting of particle asperities and subsequent fusion of particle surfaces, so as to increase interparticulate bonding. Solid bridge formation was thought to result in a reduction of void space, which in turn reduced the rate of water penetration into the compacts and consequently increased disintegration and dissolution times. It was found that the results of ultrasound-assisted compaction are influenced by formulation and US time. When ibuprofen was mixed with a second material, such as dibasic calcium phosphate dihydrate (DCP) or microcrystalline cellulose (MCC), stronger tablets were prepared by ultrasound-assisted compaction compared to the compacts containing no filler. Positive interactions were considered to have occurred due to ultrasound-induced bonding between the two materials. With an increase in DCP and MCC concentration in ibuprofen formulations, disintegration and drug dissolution rates of the tablets produced with ultrasound significantly increased. Using temperature-sensitive labels it was found that thermal changes occurred in powdered solids undergoing ultrasound-assisted compaction. Increases in the temperature of tablets were related to US amplitude and US time. With an increase in US amplitude from 5 to 13 microns, the temperature of the DCP tablet surface increased from 40 to 99 degrees C. With an increase in US time from 1 to 5 sec, the temperature of the surface of ibuprofen tablets increased from 43 to 60 degrees C. Increased tablet temperature was thought to be due to ultrasonic energy dissipation turned into heat. X-ray powder diffraction (XRD) studies of ibuprofen tablets prepared by ultrasound-assisted compaction at 32 MPa revealed that no changes in chemical or/and crystalline structure of the material occurred when ultrasound was applied for up to 5 sec (US amplitude 7 microns). An XRD study of DCP tablets produced by ultrasound-assisted compaction at 32 MPa with ultrasound of different amplitudes (5, 7, 13 microns) applied for 2 sec indicated that no material deterioration occurred in all the tested samples.

Compressive Strength↗
PubMed2003

Carbamazepine/betaCD/HPMC solid dispersions. II. Physical characterization.

Solid dispersions containing carbamazepine (CBZ) associated with beta-cyclodextrin (betaCD) and/or hydroxypropyl methylcellulose were prepared by two different methods, spray-drying or physical mixture, and characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), infrared (IR) spectroscopy, and x-ray powder diffraction analysis (XRPD) studies. Scanning electron microscopy pictures showed that spray-drying produced a mixture of hollow, spherical, and partially shrunken microparticles of homogeneous materials, whereas the physical mixtures yielded heterogeneous systems in which all individual components could be identified. Thermal and IR analyses suggest the existence of a strong interaction between CBZ and excipients in spray-dried solid dispersions, but no CBZ polymorphic transition was detected by either IR spectroscopy or XRPD analysis after the spray-drying process.

Anticonvulsants↗
PubMed2003

Different dissolution media lead to different crystal structures of talinolol with impact on its dissolution and solubility.

During the performance of dissolution tests with immediate and controlled-release talinolol tablets it was detected that the type of the buffer used as dissolution medium had a strong influence on the solubility and the dissolution behavior of the drug. It was proven that talinolol appeared in different crystal structures with strongly differing solubilities when pure water, acetate, or phosphate buffers were employed as dissolution media. The resulting crystal structures were characterized by means of light microscopy, differential scanning calorimetry, and X-ray powder diffraction. All methods were adjuvant to detect changes in talinolol crystal structures. The different solubility and dissolution properties of the talinolol salts or modifications may be viewed as a source for its incomplete and variable bioavailability. Furthermore, the food effect, described in the literature, that leads to a decrease in talinolol absorption, could be due to changes in the composition of gastrointestinal fluids leading to different talinolol crystal structures. Furthermore, it was detected that the addition of sodium chloride increases talinolol solubility and accelerates its dissolution from controlled-release tablets at concentrations between 0% and 1.25%, while an addition of sodium dodecylsulfate (SDS) as surfactant only had a solubility-improving effect at concentrations > 0.75%. At lower concentrations SDS decreased the solubility of talinolol and notably decelerated its release from controlled-release tablets.

Adrenergic beta-Antagonists↗
PubMed2004

Assessment of degree of disorder (amorphicity) of lyophilized formulations of growth hormone using isothermal microcalorimetry.

When determining the degree of disorder of a lyophilized cake of a protein, it is important to use an appropriate analytical technique. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) are the most commonly used thermoanalytical techniques for characterizing freeze-dried protein formulations. Unfortunately, these methods are unable to detect solid-state disorder at levels < 10%. Also, interpretation of DSC results for freeze-dried protein formulations can be difficult, as a result of the more complex thermal events occurring with this technique. For example, proteins can inhibit the thermally induced recrystallization of the lyophilized cake, resulting in potential misinterpretation of DSC degree of disorder results. The aim of this investigation was to study the use of isothermal microcalorimetry (IMC) in the assessment of degree of solid-state disorder (amorphicity) of lyophilized formulations of proteins. For this purpose, two formulations of growth hormone were prepared by lyophilization. These formulations consisted of the same amounts of protein, mannitol, glycine, and phosphate buffer, but differed in the freeze-drying procedure. After lyophilization, the recrystallization of the samples was studied using IMC at 25 degrees C under different relative humidities (58-75%). The effect of available surface area was studied by determining the heat of recrystallization (Q) of the samples before and after disintegration of the cakes. The results showed that, in contrast to DSC, IMC allowed detection of the recrystallization event in the formulations. Although both formulations were completely disordered and indistinguishable according to XRPD method, IMC revealed that formulation B had a different solid-sate structure than formulation A. This difference was the result of differences in the freeze-drying parameters, demonstrating the importance of choosing appropriate analytical methodology.

Calorimetry, Differential Scanning↗
PubMed2004

Development and evaluation of glyburide fast dissolving tablets using solid dispersion technique.

Glyburide is a poorly water-soluble oral hypoglycemic agent, with problems of variable bioavailability and bio-inequivalence related to its poor water-solubility. This work investigated the possibility of developing glyburide tablets, allowing fast, reproducible, and complete drug dissolution, by using drug solid dispersion in polyethylene glycol. Phase-solubility studies were performed to investigate the drug-carrier interactions in solution, whereas differential scanning calorimetry, X-ray powder diffraction, and infrared spectroscopy were used to characterize the solid state of solid dispersions. The effects of several variables related to both solid dispersion preparation (cofusion or coevaporation technique, drug-to-carrier ratio, polyethylene glycol molecular weight) and tablet production (direct compression or previous wet-granulation, tablet hardness, drug, and solid dispersion particle size) on drug dissolution behavior were investigated. Tablets obtained by direct compression, with a hardness of 7-9 Kp, and containing larger sized solid dispersions (20-35 mesh, i.e., 850-500 microm) of micronized glyburide in polyethylene glycol 6000 prepared by the cofusion method gave the best results, with a 135% increase in drug dissolution efficiency at 60 min in comparison with a reference tablet formulation containing the pure micronized drug. Moreover, the glyburide dissolution profile from the newly developed tablets was clearly better than those from various commercial tablets at the same drug dosage.

Calorimetry, Differential Scanning↗
PubMed2004

Solubilization and solid-state characterization of a poorly soluble 5-alpha reductase inhibitor.

GI197111X is a 5-alpha reductase inhibitor for the treatment of androgenetic alopecia. Equilibrium solubilities of GI197111X were determined in multiple solvents or cosolvents. A polymorph screen was conducted using suspension equilibration and solution recrystallization methods. Single crystals were grown from pyridine/water and crystal structure was determined using a Bruker SMART diffractometer. Crystal structure data were imported into Cerius2 to provide visualization of the crystal structure and calculation of the simulated X-ray powder diffraction (XRPD) pattern. The solubility of GI19711IX was low at 25 degrees C in all vehicles suitable for animal and human dosing. The solubility of 6.4 mg/mL in Capmul MCM made it the only choice for a soft gel dosage form for phase I/II. Solution recrystallization and suspension equilibration of GI197111X have produced only one crystal form. Crystal structure data: orthorhombic P2(1) 2(1) 2(1); a= 10.8960(6) A, b=11.5683(6) A, c=20.9019(11) A; unit cell volume 2634.65(24) A3; Z=4; calculated density= 1.248 g/cc. The molecule has seven chiral centers, and single-crystal analysis eliminated all possible stereo-isomers except the expected conformation or its enantiomer. Hydrogen bonds occur from both carbonyl oxygens to an H-N group. Simulated vacuum-based crystal morphology (habit) calculated using the Bravais-Friedel-Donnay-Harker, Growth Morphology, and Hartman-Perdok modules in Cerius2 was a close match to the morphology observed by light microscopy.

Calorimetry, Differential Scanning↗
PubMed1999

Investigation of the polymorphism of the angiotensin II antagonist agent MK-996.

The polymorphism of the angiotensin II antagonist agent MK-996 was studied, with particular emphasis on crystal form stability, solubility, and reproducible crystallization of the drug. X-ray powder diffraction patterns indicated differences in the crystal forms of early research and development lots. Solubility data for the different crystal forms in water at 25 degrees C are in agreement with the solution calorimetry data and indicated that crystalline form I is the thermodynamically stable polymorph of MK-996 under ambient conditions. In contrast to the other polymorphs, form I is reproducibly prepared on both the laboratory and production scale. This study examines methodology to determine the most suitable polymorph for development.

Angiotensin Receptor Antagonists↗
PubMed2003

Physicochemical evaluation of carbamazepine microparticles produced by the rapid expansion of supercritical solutions and by spray-drying.

PURPOSE: To compare the physical and physicochemical characteristics of carbamazepine microparticles prepared using two different methods: (1) the rapid expansion of supercritical solutions (RESS) and (2) the spray-drying process. METHODS: For both processes, microparticles were produced over a range of different temperatures (35 to 100 degrees C). For the RESS method, carbon dioxide was the solvent used over a pressure range of 2500 to 3500 psi. As for the spray-drying method, different organic solvents were used at atmospheric pressure. Comparison was based on morphology, crystalline structure, mean particle size, and size distribution of processed particles. The influence of process parameters on microparticles' characteristics was also investigated. Particles were analyzed using scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), thermogravimetric analyzer (TGA), and differential scanning calorimetry (DSC). RESULTS: The carbamazepine particles used as unprocessed starting material had a mean diameter of approximately 85 microm with a size distribution range between 15 and 336 microm. Microparticles produced by either the RESS or spray-drying method had a mean diameter smaller than 2 microm and a narrower size distribution range between 0.25 and 2.5 microm. SEM photomicrographs, X-ray diffractograms, and DSC spectra revealed that modification of crystal morphology was dependent on the operating conditions. CONCLUSIONS: Significant reduction in mean particle size and size distribution range of carbamazepine particles was observed by RESS and spray-drying methods. The results also demonstrate that the crystalline nature of carbamazepine particles depends on the method of production and on the operating parameters of pressure and temperature.

Carbamazepine↗
PubMed2005

Effect of solid state transition on the physical stability of suspensions containing bupivacaine lipid microparticles.

Bupivacaine lipid microparticles were prepared and evaluated as a parenteral sustained-release dosage form for postoperative pain management. Bupivacaine free base was incorporated into a molten tristearin matrix and lipid micro-particles were subsequently formed from this molten mixture by a spray-congealing process. A 3% injectable bupivacaine lipid microparticle suspension was prepared by dispersing 30% bupivacaine lipid microparticles in an aqueous medium containing carboxymethylcellulose (CMC), mannitol, and Tween 80. Upon room temperature storage, the fluid suspension gradually changed into a nonflowing semisolid (gelation) as a result of crystal growth of bupivacaine. However, suspensions prepared with bupivacaine lipid microparticles that were previously annealed at an elevated temperature remained fluid upon long-term storage. Differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD), and isoperibol solution calorimetry were used to investigate the changes in the solid-state properties of tristearin and bupivacaine in the lipid microparticles before and after the heat treatment. The DSC and XRPD results indicate that after 24 hours of heating at 40 degrees C, tristearin was completely converted from the unstable alpha form to the stable beta form. Using the isoperibol solution calorimetric method, bupivacaine was found to transform into a more stable form after the lipid microparticles were heated at 60 degrees C for 24 hours. The generation of the unstable solid forms of tristearin and bupivacaine was attributed to the resolidification of both components from the molten mixture during the spray-congealing process.

Anesthetics, Local↗
PubMed1999

Guaifenesin- and ephedrine-induced stones.

PURPOSE: We report a new type of drug-induced stone that is caused by overconsumption of preparations containing guaifenesin and ephedrine. MATERIALS AND METHODS: Clinical and stone analysis data from the Molecular Structure Laboratory at the Veterans Affairs Medical Center in Milwaukee, Wisconsin, were reviewed. Stone analysis was performed by Fourier transform infrared spectroscopy, high-resolution X-ray crystallographic powder diffraction, or both. The urine and stone material from one of the subjects were analyzed with high-performance liquid chromatography. RESULTS: Stone analysis from seven patients demonstrated metabolites of guaifenesin. High-performance liquid chromatography revealed that the stone and urine from one subject had a high content of guaifenesin metabolites and a small amount of ephedrine. Demographic data were available on five patients. Three had a history of alcohol or drug dependency. All were consuming over-the-counter preparations containing ephedrine and guaifenesin. Four admitted to taking excessive quantities of these agents, mainly as a stimulant. Hypocitraturia was identified in two individuals subjected to urinary metabolic testing. These stones are radiolucent on standard X-ray imaging but can be demonstrated on unenhanced CT. Shockwave lithotripsy was performed in two patients, and the calculi fragmented easily. CONCLUSIONS: Individuals consuming large quantities of preparations containing ephedrine and guaifenesin may be at risk to develop stones derived mainly from metabolites of guaifenesin and small quantities of ephedrine. These patients may be prone to drug or alcohol dependency.

Adult↗
PubMed2006

Synthesis and microstructure of Cd4SiS6/Si composite nanowires.

Cd4SiS6/Si composite nanowires are produced through co-thermal evaporation of CdS and Si powders with a small amount of tin sulfide as an additive. A vapor-liquid-solid growth mechanism is proposed for the anisotropic growth of the composite nanowires based on the presence of metallic tin particles at their tip-ends. Both side-by-side and core-shell composite nanowires are obtained. The product is characterized using X-ray powder diffraction and scanning electron microscopy. Detailed structural and chemical analyses of individual composite nanowires are carried out using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), electron diffraction (ED) and energy-dispersive X-ray spectroscopy. Planar defects, including microtwins and stacking faults, are abundant in a Si core, as revealed by HRTEM and selected-area ED. The formation of composite nanowires is discussed in the light of thermodynamic and kinetic aspects.

Journal Article↗
PubMed2000

The Molteno M-Sphere.

PURPOSE: To analyze a mammalian hydroxyapatite (HA) implant known as the Molteno M-Sphere, recently approved by the Food and Drug Administration of the United States. METHODS: The authors examined the implant macroscopically, with chemical analysis (x-ray powder diffraction, x-ray fluorescence spectrophotometry), and microscopically with scanning electron microscopy. Animal implantation of six Molteno M-Spheres was carried out in six adult male New Zealand albino rabbits. Implant vascularization was evaluated by means of magnetic resonance imaging and histopathologic sectioning. RESULTS: The M-Sphere was found to have multiple interconnected pores throughout with an average pore size of 300 microm to 600 microm. This implant was very light-weight (0.31 g) and fragile. It was made up of pure HA. Magnetic resonance imaging studies showed implant enhancement to its center by 4 weeks after implantation. Histopathologically, fibrovascularization occurred uniformly throughout the 4, 8, and 12-week rabbit implants. CONCLUSIONS: The M-Sphere is an alternative type of HA implant that recently has been reintroduced into the United States for use after enucleation, evisceration, or as a secondary implant. It has multiple interconnected pores allowing central fibrovascularization as early as 4 weeks in a rabbit model. Its light weight and fine trabecular framework, however, are associated with increased implant fragility when compared with other available HA implants (BioEye and FCI3 synthetic HA). The implant requires careful handling because routine handling may damage the implant. The implant is currently approved by the United States Food and Drug Administration.

Animals↗
PubMed1998

Dissolution kinetics of calcium phosphate coatings.

Plasma spray and high velocity oxy-fuel (HVOF) techniques produce coatings with varying composition and amounts of amorphous and crystalline phases. For coatings containing greater amorphous phases, a higher release of calcium ions is evident when samples are placed in Hank's calcium-free balanced salt solutions. Calcium is released from the amorphous phases in the coating, a conclusion that is supported by x-ray powder diffraction (XRD) results. Ion beam sputtering and RF magnetron sputtering under lower energy conditions produce amorphous coatings that will dissolve in a very short time period. When heat treated, crystalline phases are produced in the coatings. Heat-treated coatings are significantly more stable than the amorphous coatings. The dissolution rates of both amorphous and crystalline coatings produced by RF magnetron sputtering have been measured under constant solution conditions at pH 6.50. No reprecipitation is possible under these conditions. The amorphous coating dissolved at a significantly higher rate than the heat-treated coating. Reprecipitation of calcium phosphate onto amorphous coatings is possible in a physiological pH solution. Under these conditions, the dissolution rate of the amorphous coating is four times slower than at the pH 6.50 conditions.

Calcium↗
PubMed2003

Osteopontin is a critical inhibitor of calcium oxalate crystal formation and retention in renal tubules.

Calcium nephrolithiasis is the most common form of renal stone disease, with calcium oxalate (CaOx) being the predominant constituent of renal stones. Current in vitro evidence implicates osteopontin (OPN) as one of several macromolecular inhibitors of urinary crystallization with potentially important actions at several stages of CaOx crystal formation and retention. To determine the importance of OPN in vivo, hyperoxaluria was induced in mice targeted for the deletion of the OPN gene together with wild-type control mice. Both groups were given 1% ethylene glycol, an oxalate precursor, in their drinking water for up to 4 wk. At 4 wk, OPN-deficient mice demonstrated significant intratubular deposits of CaOx crystals, whereas wild-type mice were completely unaffected. Retained crystals in tissue sections were positively identified as CaOx monohydrate by both polarized optical microscopy and x-ray powder diffraction analysis. Furthermore, hyperoxaluria in the OPN wild-type mice was associated with a significant 2- to 4-fold upregulation of renal OPN expression by immunocytochemistry, lending further support to a renoprotective role for OPN. These data indicate that OPN plays a critical renoprotective role in vivo as an inhibitor of CaOx crystal formation and retention in renal tubules.

Animals↗
PubMed2003

Conversion of calcium oxalate to calcium phosphate with recurrent stone episodes.

PURPOSE: We have extended our previous observation that the percent occurrence of calcium oxalate stones decreased while that of calcium phosphate stones increased with each new stone event. MATERIALS AND METHODS: The National VA Crystal Identification Center has analyzed veteran patient urinary tract stones from VA hospitals throughout the United States since 1983. We reviewed the composition of 33,198 stones with emphasis on the changes in composition. More than 11,786 stones came from 5,088 recurrent stone formers. Stones were analyzed using high resolution x-ray powder diffraction and Fourier transform infrared spectroscopic techniques. When the stones were investigated as a function of time, it was determined that there was greater variability when samples were more than 30 days apart. RESULTS: The percent occurrence of whewellite, weddelite, apatite, brushite and uric acid in stones increased between 1.0% and 5.9% since our previous study. The percent occurrence of struvite decreased by 2.6%. The percent of calcium oxalate stones decreased while that of calcium phosphate stones increased with each new event. However, the total percent occurrence of all calcium containing stones did not significantly change with recurrent stone events. CONCLUSIONS: Our study suggests a strong trend for the conversion of stone disease from calcium oxalate to calcium phosphate containing stones, which could influence the progression and severity of disease.

Apatites↗
PubMed2000

Ice XII in its second regime of metastability

We present neutron powder diffraction results which give unambiguous evidence for the formation of the recently identified new crystalline ice phase [2], labeled ice XII, in completely different conditions. Ice XII is produced here by compressing hexagonal ice I(h) at T = 77, 100, 140, and 160 K up to 1.8 GPa. It can be maintained at ambient pressure in the temperature range 1.5<T<135 K. Accurate structural properties are obtained from high-resolution diffraction carried out at T = 1.5 K. At T = 140 and 160 K additionally ice III/IX is formed. The increasing amount of ice III/IX with increasing temperature gives an upper limit of T approximately 150 K for the successful formation of ice XII with the presented procedure.

Journal Article↗
PubMed2000

Origin of the high piezoelectric response in PbZr1-xTixO3

High resolution x-ray powder diffraction measurements on poled PbZr1-xTixO3 (PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the so-called morphotropic phase boundary) have shown that for both rhombohedral and tetragonal compositions the piezoelectric elongation of the unit cell does not occur along the polar directions but along those directions associated with the monoclinic distortion. This work provides the first direct evidence for the origin of the very high piezoelectricity in PZT.

Journal Article↗