Biomedical subjects

Abira Pyne

Publications and source records attributed to Abira Pyne.

10 recordsLinked to original sources

PubMed2004

Solid-vapor interactions: influence of environmental conditions on the dehydration of carbamazepine dihydrate.

The goal of this research was a phenomenological study of the effect of environmental factors on the dehydration behavior of carbamazepine dihydrate. Dehydration experiments were performed in an automated vapor sorption apparatus under a variety of conditions, and weight loss was monitored as a function of time. In addition to lattice water, carbamazepine dihydrate contained a significant amount of physically bound water. Based on the kinetics of water loss, it was possible to differentiate between the removal of physically bound water and the lattice water. The activation energy for the 2 processes was 44 and 88 kJ/mol, respectively. As expected, the dehydration rate of carbamazepine dihydrate decreased with an increase in water vapor pressure. While dehydration at 0% relative humidity (RH) resulted in an amorphous anhydrate, the crystallinity of the anhydrate increased as a function of the RH of dehydration. A method was developed for in situ crystallinity determination of the anhydrate formed. Dehydration in the presence of the ethanol vapor was a 2-step process, and the fraction dehydrated at each step was a function of the ethanol vapor pressure. We hypothesize the formation of an intermediate lower hydrate phase with unknown water stoichiometry. An increase in the ethanol vapor pressure first led to a decrease in the dehydration rate followed by an increase. In summary, the dehydration behavior of carbamazepine dihydrate was evaluated at different vapor pressures of water and ethanol. Using the water sorption apparatus, it was possible to (1) differentiate between the removal of physically bound and lattice water, and (2) develop a method for quantifying, in situ, the crystallinity of the product (anhydrate) phase.

Anhydrides↗

PubMed2004

Effect of aging on the physical properties of amorphous trehalose.

PURPOSE: The purpose of this investigation was i) to study the effect of physical aging on crystallization and water vapor sorption behavior of amorphous anhydrous trehalose prepared by freeze-drying, and ii) to determine the effects of water sorption on the relaxation state of the aged material. METHODS: Freeze-dried trehalose was aged at 100 dgrees C for varying time periods to obtain samples with different degrees of relaxation. The glass transition temperature (Tg) and enthalpic relaxation were determined by differential scanning calorimetry, and the rate and extent of water uptake at different relative humidity values were quantified using an automated vapor sorption balance. RESULTS: Annealing below the Tg caused nucleation in the amorphous trehalose samples, which decreased the crystallization onset temperature on subsequent heating. However, no crystallization was observed below the Tg even after prolonged annealing. Physical aging caused a decrease in the rate and extent of water vapor sorption at low relative humidity values. Moreover, the water sorption removed the effects of physical aging, thus effectively causing enthalpic recovery in the aged samples. This recovery occurred gradually in the glassy phase and was not associated with a glass to rubber transition. We believe this aging reversal to be due to volume expansion during water sorption in the amorphous structure. CONCLUSIONS: Thermal history of amorphous materials is a crucial determinant of their physical properties. Aging of amorphous trehalose led to nucleation below the Tg, and decrease in rate and extent of water sorption. Sorption of water resulted in irreversible changes in the relaxation state of the aged material.

Absorption↗

PubMed2004

Effect of preparation method on physical properties of amorphous trehalose.

PURPOSE: To determine the effect of preparation method on the physical properties of amorphous trehalose. METHODS: Amorphous anhydrous trehalose was prepared by four different methods. viz., freeze-drying, spray-drying, dehydration, and melt quenching. The glass transition temperature (Tg), enthalpic relaxation behavior, and crystallization were studied by differential scanning calorimetry, whereas X-ray diffractometry was used for phase identification. The rate and extent of water uptake at different relative humidity values were also obtained. RESULTS: Though the enthalpic relaxation and crystallization behaviors were influenced by the method of preparation of amorphous trehalose, the Tg and fragility were not. The phase prepared by dehydration showed the highest enthalpic recovery at Tg, indicating that aging may have occurred during preparation. Among the four methods used, trehalose prepared by dehydration had the highest tendency to crystallize, whereas there was no crystallization in melt-quenched amorphous trehalose. The method of preparation influenced not only the rate and extent of water sorption but also the phase crystallized. Water vapor sorption removed the effects of structural history in the amorphous phase formed by dehydration. CONCLUSIONS: The method of preparation strongly influenced the pharmaceutically relevant properties of amorphous trehalose. The resistance to crystallization can be rank ordered as trehalose prepared by dehydration < freeze-dried approximately spray-dried < melt-quenched. The rate of water sorption can be rank ordered as trehalose prepared by dehydration < freeze-dried < spray-dried.

Chemical Phenomena↗

PubMed2003

Solute crystallization in mannitol-glycine systems--implications on protein stabilization in freeze-dried formulations.

The use of mannitol in combination with glycine has resulted in stable freeze-dried protein formulations. Our objectives were to (1) study solute crystallization in ternary systems containing mannitol, glycine, and water during all the stages of freeze drying as a function of processing conditions and formulation variables; (2) investigate the effect of sodium phosphate buffer salts on the crystallization of both mannitol and glycine and vice versa; and (3) investigate the effects of these excipients in a freeze-dried lactate dehydrogenase (LDH) formulation. X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to study the frozen aqueous solutions. Phase transitions during primary and secondary drying were monitored by simulating the entire freeze-drying process in situ in the sample chamber of the diffractometer. LDH activity after freeze drying was determined spectrophotometrically. In frozen aqueous solutions containing mannitol and glycine, each solute influenced the extent of crystallization of the other. The solutes crystallized as delta-mannitol and beta-glycine during primary drying. Glycine had a stronger tendency to crystallize, while it was easier to influence mannitol crystallization. The buffer salts inhibited the crystallization of mannitol and glycine. However, in some cases, during primary drying, glycine crystallization was followed by that of disodium hydrogen phosphate dodecahydrate. The latter underwent dehydration forming an amorphous anhydrate. It was possible to correlate the extent of crystallization of mannitol and glycine in the lyophile with the retention of protein activity. An increase in buffer concentration decreased the crystallinity of mannitol and glycine. This translated to increased retention of protein activity.

Buffers↗

PubMed2003

The effect of additives on the crystallization of cefazolin sodium during freeze-drying.

PURPOSE: To monitor the phase transitions during freeze-drying of cefazolin sodium (I) as a function of process and formulation variables. METHODS: Aqueous solutions of I were frozen under controlled conditions in the sample chamber of a variable temperature X-ray powder diffractometer (XRD). The instrument was modified so that the chamber could be evacuated and the samples dried under reduced pressures. Thus, the entire freeze-drying process was carried out in the XRD holder with real time monitoring of the phase transitions during the different stages of freeze-drying. RESULTS: When aqueous solutions of cefazolin sodium (10% w/w) were cooled to -40 degrees C, the XRD pattern revealed only the crystallization of ice. Annealing the frozen sample led to the crystallization of I as the pentahydrate. Differential scanning calorimetry revealed that the presence of isopropyl alcohol (IPA) (5% w/w) led to a decrease in the Tg', the glass transition temperature of the system, and lowered the temperature of crystallization. The crystallization was studied at -8 and at -15 degrees C in the XRD, and, as expected, more rapid crystallization was observed at the higher temperature. Primary drying at -8 degrees C led to the dehydration of the pentahydrate, resulting in a poorly crystalline product. Again, XRD permitted real time monitoring of the decrease in intensities of some characteristic peaks of the pentahydrate. The in situ XRD technique also enabled us to study the effects of processing conditions (different primary and secondary drying temperatures) and crystalline bulking agents on the solid-state of I in the lyophile. When I was lyophilized using mannitol or glycine as an additive, without an annealing step, the drug was X-ray amorphous although the additive crystallized. When annealed and freeze-dried, I remained crystalline in the presence of glycine but not in the presence of mannitol. CONCLUSIONS: The in situ XRD technique has enabled us to characterize the phase transitions during freeze-drying of cefazolin sodium in multicomponent systems.

Cefazolin↗

PubMed2003

Crystalline to amorphous transition of disodium hydrogen phosphate during primary drying.

PURPOSE: To monitor the phase transitions during freeze-drying of disodium hydrogen phosphate. METHODS: The variable temperature sample stage of the X-ray diffractometer (XRD) was attached to a vacuum pump, which enabled the entire freeze-drying process to be carried out in the sample chamber. The phase transitions during the freeze-drying cycle were monitored in real time by XRD. Aqueous buffer solution (containing disodium hydrogen phosphate and sodium dihydrogen phosphate) was cooled at 2 degrees C/min from room temperature to -70 degrees C. It was then heated to -25 degrees C and subjected to primary drying for 2 h at a chamber pressure of approximately 100 mTorr, followed by secondary drying at -10 degrees C. RESULTS: In the frozen solution, disodium hydrogen phosphate had crystallized as the dodecahydrate (Na2HPO4 x 12H2O) as was evident from its characteristic lines at approximately 5.37, 4.27, and 2.81 angstroms. Primary drying for 2 h resulted in ice sublimation, and the complete disappearance of the dodecahydrate peaks. CONCLUSION: The dehydration of the crystalline dodecahydrate resulted in an amorphous anhydrate. Thus the amorphous nature of the end product is a result of phase transitions during the process and do not reflect the solid-state of the ingredients during the entire process.

Crystallization↗

PubMed2003

Determination of glass transition temperature and in situ study of the plasticizing effect of water by inverse gas chromatography.

PURPOSE: To use an inverse gas chromatographic (IGC) method to determine the glass transition temperature (Tg) of some amorphous pharmaceuticals and to extend this technique for the in situ study of the plasticizing effect of water on these materials. METHODS: Amorphous sucrose and colyophilized sucrose-PVP mixtures were the model compounds. Both IGC and differential scanning calorimetry (DSC) were used to determine their Tg. By controlling the water vapor pressure in the IGC sample column, it was possible to determine the Tg of plasticized amorphous phases. Under identical temperatures and vapor pressures, the water uptake was independently quantified in an automated water sorption apparatus. RESULTS: The Tg of the dry phases, determined by IGC and by DSC, were in very good agreement. With an increase in the environmental relative humidity (RH), there was a progressive decrease in Tg as a result of the plasticizing effect of water. Because the water uptake was independently quantified, it was possible to use the Gordon-Taylor equation to predict the Tg values of the plasticized materials. The predicted values were in very good agreement with those determined experimentally using IGC. A unique advantage of this technique is that it provides complete control over the sample environment and is thus ideally suited for the characterization of highly reactive amorphous phases. CONCLUSIONS: An IGC method was used (a) to determine the glass transition temperature of amorphous pharmaceuticals and (b) to quantify the plasticizing effect of water on multicomponent systems.

Calorimetry, Differential Scanning↗

PubMed2002

Solid-state properties of creatine monohydrate.

Creatine monohydrate (CM) is a nutritional supplement and an ergogenic aid for athletes. It appears to increase lean body mass, high-intensity power output and strength in healthy humans. The crystal structure of creatine monohydrate has previously been reported. However, little information is available on its solid-state properties. In this investigation, creatine monohydrate was subjected to Thermal Analyses, Karl-Fisccher Titrimetry (KFT), Scanning Electron Microscopy (SEM), and Variable Temperature X-ray Powder Diffractometry (VTXRD) to characterize its solid-state properties. The results of this study suggested that commercially available creatine monohydrate dehydrates at about 97-125 degrees C. A phase transition after dehydration was confirmed by X-ray diffraction studies. This dehydrated phase at a temperature above 230 degrees C undergoes intramolecular cyclization with a loss of an additional mole of water to form creatinine. Creatinine finally melts with decomposition at about 290 degrees C. VTXRD, confirmed that the above solid-state thermal transformation was kinetically driven, and occurred within a narrow temperature range. Mass Spectrometric (MS) studies further indicated a possible dimerization of creatinine formed during the solid-state transformation.

Chemical Phenomena↗

PubMed2002

Crystallization of mannitol below Tg' during freeze-drying in binary and ternary aqueous systems.

PURPOSE: To characterize the phase transitions in a multicomponent system during the various stages of the freeze-drying process and to evaluate the crystallization behavior below Tg' (glass transition temperature of maximally freeze-concentrated amorphous phase) in frozen aqueous solutions and during freeze-drying. METHODS: X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to study frozen aqueous solutions of mannitol with or without trehalose. By attaching a vacuum pump to the low-temperature stage of the diffractometer, it was possible to simulate the freeze-drying process in situ in the sample chamber of the XRD. This enabled real-time monitoring of the solid state of the solutes during the process. RESULTS: In rapidly cooled aqueous solutions containing only mannitol (10% w/w), the solute was retained amorphous. Annealing of frozen solutions or primary drying. both below Tg', resulted in crystallization of mannitol hydrate. Similar effects were observed in the presence of trehalose (2% w/w). At higher concentrations (> or =5% w/w) of this noncrystallizing sugar. annealing below Tg' led to nucleation but not crystallization. However, during primary drying, crystallization of mannitol hydrate was observed. CONCLUSIONS: The combination of in situ XRD and DSC has given a unique insight into phase transitions during freeze-drying as a function of processing conditions and formulation variables. In the presence of trehalose, mannitol crystallization was inhibited in frozen solutions but not during primary drying.

Cold Temperature↗

PubMed2002

Crystallization behavior of mannitol in frozen aqueous solutions.

PURPOSE: To study the effect of cooling rate, the influence of phosphate buffers and polyvinylpyrrolidone (PVP) on the crystallization behavior of mannitol in frozen aqueous solutions. METHODS: Low-temperature differential scanning calorimetry and powder X-ray diffractometry were used to characterize the frozen solutions. RESULTS: Rapid cooling (20 degrees C/min) inhibited mannitol crystallization, whereas at slower cooling rates (10 degrees C and 5 degrees C/min) partial crystallization was observed. The amorphous freeze-concentrate was characterized by two glass transitions at -32 degrees C and -25 degrees C. When the frozen solutions were heated past the two glass transition temperatures, the solute crystallized as mannitol hydrate. An increase in the concentration of PVP increased the induction time for the crystallization of mannitol hydrate. At concentrations of > or =100 mM, the buffer salts significantly inhibited mannitol crystallization. CONCLUSIONS: The crystallization behavior of mannitol in frozen solutions was influenced by the cooling rate and the presence of phosphate buffers and PVP.

Crystallization↗