Freeze drying solids

Native, multi-subunit KLH also should not be frozen. Freeze-thaw effects cause extensive denaturation and result in considerable amounts of insoluble material. Commercial preparations of native KLH are typically freeze-dried solids that no longer fully dissolve in aqueous buffers and do not display the protein s typical blue color due to loss of chelated copper. The partial denatured state of these products often makes conjugation reactions difficult. 

Solution of polymeric products Freeze-drying Solid matter... 

For activity assays, proteinase solutions were made fresh daily (10 mg freeze-dried solids in 1 ml pH 10.0 phosphate buffer, 0.1 M). Two ml of the proteinase, 0.5 ml of substrate (azocasein or other proteins in pH 10 buffer), 0.3 ml of 0.1% EDTA, and deionized water were made up to a volume of 3.5 ml. Reaction tubes were incubated in a 40°C water bath for 1 hr, then the reaction was stopped by addition of 1 ml 5% TCA. After removal of the precipitated proteins by centrifugation, absorbance was read at 366 nm (for azocasein) or by the Lowry method (15) for other... 

Freeze drying is used to remove water from heat-sensitive substances at low temperature by the process of sublimation, where water is removed via a phase change from a solid to a vapor without passing through a liquid state. This takes place below the triple point of water (Fig. 1), at approximately 0°C and 4.5 mm of mercury (Hg). In addition, when freeze drying is carried out properly, the freeze-dried solid has a relatively high specific surface area, which promotes rapid, complete reconstitution. 

Glass transitions, both in frozen systems and in freeze-dried solids, can be difficult to detect. This may be caused by the small heat capacity change associated with the glass transition, a broad glass transition region, or both. Interpretation is made more uncertain by baseline drift or other noise. In addition, other thermal events at temperatures close to the glass transition, such as enthalpy recovery or crystallization, may disguise the heat capacity... 

A subtle aspect of stability analysis of freeze-dried products in vials with rubber stoppers is the tendency for water vapor to be transferred from the stopper to the solid during storage. Representative data for residual moisture as a function of time at different temperatures are shown in Figure 11. As expected, the residual moisture level increases more rapidly at higher temperature, but the plateau level is independent of temperature as equilibrium is established between the freeze-dried solid and the stopper. The extent to which this is observed depends on several factors. First, the nature of the rubber stopper formulation affects the diffusivity of water in the rubber. Second, the processing of the stopper can affect the level of residual moisture present. It is not uncommon for extended drying of the stopper to be necessary to minimize residual moisture. Finally, the mass of the freeze-dried solid determines the extent to which the percent residual moisture is affected by water vapor transfer from the stopper, where large cakes may be relatively unaffected by the small amount of water vapor that is... 

Figure 11 Changes in residual moisture during storage of freeze-dried solids due to water vapor transfer from the stopper at different storage temperatures 5°C (diamonds), 25°C (squares), and 40°C (triangles).

Shalaev et al. (37) examined the influence of citric acid on the acid-catalyzed inversion of sucrose in the freeze-dried solid state. Even with less than 0.1% residual moisture, the colyophilization of sucrose with acidic substances can produce reducing sugars capable of further reaction with other formulation components that are susceptible to such reactions. 

Oguchi and coworkers examined the decarboxylation behavior of -aminosalicylic acid (PAS) as a freeze-dried solid under thermal stress conditions (80°C) in the presence of the excipients pullulan (a linear polysaccharide which can not form inclusion complexes with PAS) and a-cyclodextrin (39). The solid-state stability was shown to correlate with the fraction of amorphous PAS. Increasing relative amounts of pullulan resulted in higher fractions of amorphous PAS. Rapid freezing (liquid nitrogen) was shown to result in a greater relative amount of amorphous drug, as expected. 

Most tritiated sugars are best stored in aqueous solution, sometimes containing a small proportion of ethanol. Under these conditions, radiolysis usually does not exceed 5 to 10% per year. In the frozen state, between 0° and —196°, the rate of decomposition can be high, presumably due to concentration of the sugar in pockets on freezing.87 Nucleotides are stored at —20° in 50% ethanol, which acts as a free-radical scavenger,68 and decompose at the rate of 12% per year polymers should be stored as freeze-dried solids. 

Ten milligrams of the Step 3 product were dissolved in 1 ml of dimethyl sulfoxide and then removed by freeze-drying. Thereafter 1 ml of 10% sucrose was added to the hydrate, and the freeze-dried solids were re-dissolved to form a suspension. After ultra-sonicating for 10 minutes, polymer nanoparticles were formed. 

We are now at the very beginning of these investigations, but we think that low-temperature thermoluminescence applied to freeze-dried solids is susceptible... 

Chan, H.-K. Au-Yeung, J.K.-L. Gonda, I. Water distribution in freeze-dried solids containing multiple components. Pharm. Res. 1996, 13 (suppl), S-216. 

Most freeze-dried products contain several components in addition to the drug or active component. These additional components, called excipients, are intended to serve a specific function, normally related to stability or process, and may constitute the major fraction of the freeze-dried solid. 

Dual-chamber syringe. For delivery of two established vaccines (e.g., polyribosyl ribitol phosphate conjugated to tetanus toxoid and diphtheria-tetanus-whole cell pertussis and inactivated poliovirus vaccine) at the same time, a dual-chamber syringe delivery system can be used. The proximal chamber may contain a vaccine in the freeze-dried solid state, and the distal chamber contains a vaccine in the liquid formulation that allows reconstitution of the vaccine in the proximal chamber. The immune response by the dualchamber delivery of vaccination was equivalent to that by the separate-injection method of vaccination. The dual-chamber syringe can be used for safe and effective delivery of two different vaccines that are not yet available as a single formulation for pediatric applications. ... 

Chan HK, Au-Yeung KL, Gonda I. Development of a mathematical model for the water distribution in freeze-dried solids. Pharm Res 1999 16(5) 660-665. 

Izutsu K, Ocheda SO, Aoyagi N, Kojima S. Effects of sodium tetraborate and boric acid on nonisothermal mannitol crystallization in frozen solutions and freeze-dried solids. Int Pharm 2004 273(1) 85-93. 

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