Drying and gas or vapor contact with solids – Apparatus – Vacuum
Patent
1997-11-17
1999-10-12
Bennett, Henry
Drying and gas or vapor contact with solids
Apparatus
Vacuum
34284, 34290, 34297, 62345, 62381, F26B 1330
Patent
active
059640430
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of International Application PCT/GB96/00597, filed Mar. 14, 1996, which designated the U.S.
The present invention relates to a novel freeze-drying (lyophilisacion) process. This process is particularly advantageous for freeze-drying pharmaceutical products. The invention also includes the lyophilised products produced by the process.
Freeze-drying or lyophilisation, is used generally to increase the stability and hence storage life of materials. As such it is particularly useful where a material is known to be unstable or less stable in aqueous solution, as is often the case with pharmaceutical materials.
In its simplest form freeze-drying consists of freezing the aqueous material in a vial and then subjecting the material to a vacuum and drying.
The conventional method of freeze-drying is to load magazines full of vials onto chilled shelves in a sealed freeze-drying chamber. The shelf temperature is then reduced to freeze the product. At the end of the freezing period, the aqueous material is frozen as a plug at the bottom of the vial. The pressure in the chamber is then reduced and simultaneously the shelves are heated thereby causing the frozen water to sublime leaving a freeze-dried plug in the bottom of the vial (FIG. 4A). The whole lyophilisation cycle normally can take 20 to 60 hours, depending on the product and size of vial.
The disadvantages of this conventional method are as follows: necessarily be human operators to load the trays of vials into the freeze-drying chamber, which leaves the product open to contamination; room is taken into account; of space, which is necessarily very expensive because it must be maintained clean or sterile to a high standard; and such as high-speed in line filling, transfer to holding tables, and transfer to and from trays.
These operations risk vial damage or contamination, create particles in the clean area, and require operator supervision.
European patent EP-A-0048194 discloses a method of "shell-freezing" material such that the resulting lyophilised product forms a relatively thin coat or "shell" in the vial. In this method, the aqueous material is placed a vial which is then rotated slowly on its side in a freezing bath. The shell-frozen product is then loaded into a conventional lyophilisation chamber and dried over a six hour cycle (page 7).
However, although this method allegedly results in a "shell frozen" material, distribution can be non-uniform. Also relatively long lyophilisation times may still be required. The above rolling method also suffers from other disadvantages, including: above a certain limit some liquid would pour out; longer drying time); and present invention).
U.S. Pat. No. 3,952,541 describes an apparatus for a freezing aqueous solution or suspension which comprises a refrigerated tank which has at least one plate, which carries the materials to be frozen, mounted on a shaft to rotate at about 10 to 20 revolutions per minute around the base of the tank. The tank is adjustable to tilt at (for example) a 45.degree. angle, and a fan mounted inside the roof of the tank blows cold air around the refrigerated tank. Once the product is frozen, it appears that the vials would have to be transferred to a separate drying chamber, for approximately 111/2 hours. The whole lyophilisation cycle takes 12 hours and the product obtained is of an internally concave paraboloid form.
The disadvantages of this process is that the time is still long (12 hours), the process must be operated batchwise and it is not capable of handling a large throughput of vials. Furthermore, when transferring the frozen open product from the refrigerated tank to a drying chamber, there must apparently be human operator contact and the product must be maintained in a frozen stage until transferred.
British patent no. 784784 discloses a freeze-drying process in which vessels containing liquid material are subjected to a centrifugal force at a low vacuum. The low vacuum causes the water to be released and the effect of centrifuging helps
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MacMichael Donald B. A.
Oughton Dominic M. A.
Smith Philip R. J.
Bennett Henry
Glaxo Wellcome Inc.
Wilson Pamela A.
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