Abira Pyne

Effect of Preparation Method on Physical Properties of Amorphous Trehalose

AbstractPurpose. 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 mF spray-dried < melt-quenched. The rate of water sorption can be rank ordered as trehalose prepared by dehydration < freeze-dried < spray-dried.

Crystallization Behavior of Mannitol in Frozen Aqueous Solutions

AbstractPurpose. 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°C/min) inhibited mannitol crystallization, whereas at slower cooling rates (10°C and 5°C/min) partial crystallization was observed. The amorphous freeze-concentrate was characterized by two glass transitions at -32°C and -25°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 ≥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.

Effect of Aging on the Physical Properties of Amorphous Trehalose

AbstractPurpose. 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°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.

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

AbstractPurpose. 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 (≥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.

Phase Transitions of Glycine in Frozen Aqueous Solutions and During Freeze-Drying

AbstractPurpose. To study the solid-state and phase transitions of glycine, (i) in frozen aqueous solutions, and (ii) during freeze-drying. Methods. X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to analyze the frozen systems. In situ freeze-drying in the sample chamber of the diffractometer enabled characterization of phase transitions during freeze-drying. Results.Transitions in frozen systems. Rapid (20°C/min) or slow (2°C/min) cooling of aqueous solutions of glycine (15% w/w) to −70°C resulted in crystallization of β-glycine. Annealing at −10°C led to an increase in the amount of the crystalline phase. When quench-cooled by immersing in liquid nitrogen, glycine formed an amorphous freeze-concentrate. On heating, crystallization of an unidentified phase of glycine occurred at ∼ \-65°C which disappeared at ∼ −55°C, and the peaks of β-glycine appeared. Annealing caused a transition of β- to the γ- form. The extent of this conversion was a function of the annealing temperature. Slower cooling rates and annealing in frozen solutions increased the crystalline β-glycine content in the lyophile. Freeze-drying of quench-cooled solutions led to the formation of γ-glycine during primary drying resulting in a lyophile consisting of a mixture of β- and γ-glycine. The primary drying temperature as well as the initial solute concentration significantly influenced the solid-state of freeze-dried glycine only in quench-cooled systems. Conclusions. The cooling rate, annealing conditions and the primary drying temperature influenced the solid-state composition of freeze-dried glycine.

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

AbstractPurpose. 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.

Crystalline to amorphous transition of disodium hydrogen phosphate during primary drying

AbstractPurpose. 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°C/min from room temperature to −70°C. It was then heated to −25°C and subjected to primary drying for 2 h at a chamber pressure of ∼100 mTorr, followed by secondary drying at −10°C. Results. In the frozen solution, disodium hydrogen phosphate had crystallized as the dodecahydrate (Na2HPO4⋅12H2O) as was evident from its characteristic lines at ∼5.37, 4.27, and 2.81 Å. 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.

The Effect of Additives on the Crystallization of Cefazolin Sodium during Freeze-Drying

AbstractPurpose. 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°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°C in the XRD, and, as expected, more rapid crystallization was observed at the higher temperature. Primary drying at -8°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.

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.