Drying and gas or vapor contact with solids – Process – By centrifugal force
Reexamination Certificate
2000-01-13
2002-06-25
Esquivel, Denise L. (Department: 3749)
Drying and gas or vapor contact with solids
Process
By centrifugal force
C034S311000, C034S313000, C034S314000, C034S315000, C034S316000, C034S321000, C034S322000, C034S323000, C034S324000, C034S325000, C034S326000, C034S337000, C034S338000, C034S341000, C034S317000, C034S328000, C034S329000
Reexamination Certificate
active
06408536
ABSTRACT:
BACKGROUND OF THE INVENTION
Proteins are present in many commercially available preparation forms. In particular, proteins are present as the active ingredient in some pharmaceutical medicaments. For the preparation of these preparation forms, it is beneficial to use the proteins in crystalline form. As well as being easier to handle in crystalline form proteins as dry crystals are, more stable than, for example, proteins in dissolved form.
As an example, the preparation of a pharmaceutical preparation containing the hormone insulin as active ingredient, uses the protein insulin in crystalline form. Crystallized insulin is stable, for example, at a temperature of −20° C. over a number of years.
Crystalline forms of proteins having a molecular weight of up to several hundred thousand daltons and peptides having a lower molecular weight are known. The amino acid sequence of the proteins can either be identical to a naturally occurring sequence or it can be changed relative to the natural form. In addition to containing amino acid chains, the proteins can also contain sugar radicals or other ligands as side chains. The proteins may be isolated from natural sources, or the protein may be prepared by genetic engineering or synthetically, or the proteins may be obtained by a combination of these processes.
In aqueous solution, proteins have a three-dimensional structure of greater or lesser complexity which is based on a specific spatial folding of the amino acid chains. The intact structure of a protein is essential for its biological action. During crystallization of the proteins from aqueous solutions, this structure is largely retained. The crystal structure of a protein is predominantly determined by its amino acid sequence. Another factor determining crystal structure is, for example, inclusions of low molecular weight substances, such as, for example, metal ion salts and water molecules. In particular, the presence of a certain amount of intracrystalline water molecules (water of crystallization) is necessary for the stability of the crystal structure of proteins.
For example, insulin crystals require an optimum residual water content (roughly between 1 and 7%). If the crystals are overdried and too low a moisture content is achieved, then the water of crystallization has already been removed from the crystals. As a result, the chemical stability of insulin is adversely affected, resulting, for example, in the formation of higher molecular weight compounds. It is assumed that the higher molecular weight fractions in the insulin are responsible for immunological incompatibility reactions. In the extreme case, insulin can be denatured to the extent that the crystals are no longer soluble in aqueous media. If, on the other hand, crystals with too high a moisture content are obtained upon drying, then there is too much water between the individual crystals. The insulin is partly dissolved in this intercrystalline water. The stability of the dissolved insulin is, however, significantly lower than that of solid forms.
It is known that protein crystals, in particular insulin crystals, can be dried by isolating the crystals from a crystal suspension by filtration and drying the filter cake under reduced pressure at a temperature above 0° C. It is also known that the drying process can be accelerated by replacing the intercrystalline water with ethanol prior to drying. During drying, the crystals are distributed in a thin layer on drying sheets or are agitated on the filter.
In another process, the protein crystals, for example insulin crystals, are frozen as an aqueous suspension at a temperature below 0° C. on drying sheets and then freeze-dried under reduced pressure.
In both processes mentioned, the attainment of neither a defined nor optimal residual moisture content in the dried crystals is adequately ensured. In both processes, the drying process is kinetically controlled to the end and must be terminated at a specific time in order to avoid overdrying. Experience shows that it is difficult to determine the correct point in time to terminate the drying. The resulting moisture content of the crystals depends not only on the thickness of the layer on the drying sheet, but also on the size of the crystals (or their surface area). Since the crystallization process leads to insulin crystals having a size distribution of varying width, the crystals dried in a kinetically controlled process consist of a mixture of dryer small crystals and moister large crystals.
Another disadvantage of these processes is that it is very difficult to automate charging and emptying of the equipment used for drying. Thus, the operation of charging and emptying still largely requires manual work, which harbors the risk of contamination by germs and foreign particles. For example, the currently valid pharmacopeia demand that crystalline insulin for the preparation of pharmaceutical preparations must be low in germs but not germ-free. Therefore a need exists for a process of preparing a protein preparation where the process provides crystals with a uniform water content without the risk of contamination.
SUMMARY OF THE INVENTION
The present invention comprises a process for drying protein crystals starting from an aqueous protein crystal suspension, which comprises drying the protein crystal suspension in a centrifugal dryer.
In one embodiment of the invention the process for drying protein crystals starting from an aqueous protein crystal suspension encompasses filtering off the protein crystals from the aqueous protein crystal suspension, and subsequently bringing the protein crystals into a drying medium which consists of a mixture of water and a nonaqueous solvent which is miscible with water in any ratio and which has a lower vapor pressure than water.
DETAILED DESCRIPTION OF THE INVENTION
The present invention involves a process for preparing a protein preparation which preferably comprises the following steps:
1. Filtering off the crystals from an aqueous suspension.
2. Washing the filter cake.
3. Replacing the wash liquid with a drying medium.
4. Spindrying the filter cake.
5. Detaching the filter cake from the filter and converting it into a fluidized bed.
6. Drying the crystals in the fluidized bed with a stream of moistened nitrogen.
7. Emptying the dried crystals using a nitrogen pressure surge into a flanged container.
Accordingly, the present invention relates to a process for drying protein crystals starting from an aqueous protein crystal suspension, which comprises drying the protein crystal suspension in a centrifugal dryer.
For the drying process described, it is particularly advantageous if the detached filter cake can be converted into a fluidized bed. The experiments, carried out in a commercially available dryer, have shown that if the intercrystalline water was not replaced for one of the drying media described below, it was not possible to generate a fluidized bed; a mixture of crystal aggregates of varying size formed instead, making uniform drying impossible.
Other experiments have shown that by replacing the intercrystalline water with a pure nonaqueous drying medium, e.g. 100% strength ethanol or 100% strength propanol, only the intracrystalline water (water of crystallization) remaining in the protein crystals, is it possible to produce a fluidized bed. However, during the subsequent drying phase, the drying medium could not adequately be removed even after a prolonged drying time. The dried products had a residual content of drying medium of more than 5 %. On the other hand, some of the water of crystallization had already been removed during the drying time.
Surprisingly, it has now been found that by replacing the intercrystalline water with a drying medium which consisted of a mixture of water and a nonaqueous substance, it was possible to avoid the disadvantages mentioned. After replacing the intercrystalline water with one of the drying media described below, it was possible to produce a fluidized bed from the detached filter cake and to dry the crystals satisfacto
Deusser Rolf
Kraemer Peter
Thurow Horst
Aventis Pharma Deutschland GmbH
Esquivel Denise L.
Heller Ehrman White and McAuliffe
Shulman Mark
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