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Effect and Significance on Extending the Shelf Life of Finished Drug by Freeze Drying Methods

As we know, lyophilization is a kind of preservation technology, by which the material is cooled below its eutectic temperature or glass transition temperature firstly to be solidified completely, then dried in vacuum space at low temperature by sublimation drying and desorption drying till 95% - 99% of moisture is removed. The product can be stored at room temperature or 4 oC for a long time. Lyophilization has become an important technique for the preservation of heat-sensitive pharmaceuticals. Meanwhile the process of freeze drying may greatly affect the quality of the products.
Lyophilization technique is widely applied in pharmaceutical industry, especially for producing dosage of injection. The stability of drug molecule is the key factor which affects the dosage selected by companies, liquid injection or powder injection. As studied, molecules show different structures and physical-chemical properties, according to which scientists like to classify injections as large molecules and small molecules, e.g. Chemical drug, such as Omeprazole, Pantoprazole, Vancomycin and so on, belongs to category of small molecule; Protein drug, such as Rituximab, Etanercept and so on, belongs to large molecule; Vaccine, such as DPT, Typhoid, varicella, belongs to large molecule; Probiotic, such as lactic acid bacteria, bifidobacterium, and so on, belongs to large molecule.
Generally speaking, the stability of large molecule is unstable in liquid solution, so injections with large molecule are frequently found in powder dosage, and nearly no liquid injections are found. Injections for small molecules are flexible, companies can choose either dosage form for injections. However, unique injection dosage form can often be searched for designated drug molecule in most cases, such as classic drug of antibiotic, Kanamycin injection, that is only in liquid injection. Streptomycin sulfate, which is another kind of antibiotic, is only produced in power injection dosage. The reason for above phenomenon is that companies like to choose the optimal dosage form with consideration of stability and economy. Lyophilization process is an energy cost process which contributes to the cost of production. It is better to choose liquid form when drug molecule is much stable. But also some existing data shows the good effect of lyophilization on extending the drug shelf life with comparison of two dosage forms. E.g. Cisplatin, luckily with both liquid and powder form injection, showed 1 year and 4-years shelf respectively, which can also be considered as the evidence of stability enhancement by lyophilization process.
In the year 2016, 104 injectables were approved by FDA, 43 of which are in lyophilized powder form, including all categories of NDA, BLA, and ANDA. It can be speculated that these approved drugs are or will be copied to all over the world. So powder injection shows promising market in the future, and any company who grasps this wonderful chance and key lyophilization technique will win in the end.