LIOFILIZATION: consists in the removal of water from the drug by sublimation; the drug is frozen in lyophilisers which, in particular conditions of pressure and temperature (taking into account the water state diagram), cause it to go away by sublimation (direct passage from the solid state to the gaseous state, without passing through the state liquid). It is a method that guarantees the removal of water from the drug, to reach percentages even lower than 5% very quickly.
Freeze-drying is applied to particularly rich sources of water, which for this reason risk going quickly to post-harvest degradation processes. This technique is applied precisely to avoid such alterations and allow a good preservation of the drug; it is a very expensive method but also quite common.
The modern freeze-drying and drying processes (small closed room and dynamic dryer) guarantee the best preservation of the drug over time. The small closed room is the best compromise for obtaining a temporal block of hydrolytic enzymes and preventing the non-reproduction of bacteria, molds and fungi; moreover, the temperature favors the disinfection of the drug itself.
In addition to those seen so far, there are other methods to promote the duration of a drug; the most used are STABILIZATION and CONSERVATION (addition of preservatives). Both determine an inhibition of enzymatic activity without limits over time, because they alter the structures and functionalities of the enzymes, causing them to be denatured.
The process of stabilization denatures the enzymes in an irreversible way, therefore the drug suffers alteration only if attacked by external agents, while it cannot undergo alterations from endogenous activity. In fact, stabilization is a drastic process that takes place through the use of an autoclave and appropriate solvents; the most suitable drug to be stabilized is that very easily and rapidly subject to degradation by endogenous enzymatic activity. The stabilization process must therefore be carried out immediately after the source is collected.
The autoclave is a "pressure cooker" where temperature and pressure (stable at certain values) play a fundamental role in the stabilization process; the solvent used can be alcohol or acetone. The fresh drug is placed inside a basket filled with solvent, inside the autoclave. The temperature and pressure are then brought to constant levels: 120 ° C for the temperature, while the pressure increases at intervals of 0.5 units up to two or three times higher than atmospheric values. When the pressure has reached 0.5 units above atmospheric pressure, and the temperature 105-110 ° C, the drug is in conditions suitable for the actual stabilization, which is continued for a time varying from 5 to 15 minutes . The correct execution of the stabilization process requires that the operating conditions limit the leakage of the vacuolar juice from the drug as much as possible; it is correctly performed when the passage of this juice in the solution is practically not significant.
The autoclave stabilization process leads to the complete and total denaturation of proteins and enzymes (thanks to the high temperatures and pressures reached). Thus, these protein molecules permanently lose their functional characteristics; this is why stabilization is an irreversible process. The stabilized drug will be altered only if exposed to unfavorable exogenous factors.
The drug, once stabilized, is not ready for use, because it is still immersed in the solvent; this liquid will be removed by placing it in a stove (80 ° C). After a certain period at these temperatures the drug is dry, because together with the solvent the water is also removed. Ultimately, the drug is reduced to powder so that it is ready for health use: stabilized and powdered.
If in the autoclave, inside the solvent, the quantity of active principles is negligible, then the stabilization took place correctly. If, on the other hand, this quantity is appreciable, the process has not occurred correctly; in this case, there are particular procedures for recovering the drug dispersed therein (the solvent is removed by evaporation and the active principles thus obtained are incorporated into the dried and powdered drug).
To remember: stabilization is a process adopted to improve the conservation of those drugs that undergo rapid post-harvest endogenous degradation; however, the stability of active principles must always be considered. If for example the drug is highly degradable and the active principles are thermolabile, it is evident that it cannot be stabilized, since the temperatures reached are too high to maintain its quality.
