When we think about drying process in pharmaceutical manufacturing process, we think of application of heat for process of various drying process .
Heat can not be applied to some drugs like, antibody containing immunological preparations, semi-synthetic penicillins, cephalosporins, and serums as they are very unstable even at temperature like room temperature (25 C ) at the same time such drugs are required to be free from water and other solvents and are also required to be sterile.
Such drugs can be made free from water or any other solvent by process of freeze drying which is also known as Lyophilizasation. In the process of freeze drying ( Lyophilizasation ) liquid is transformed in to solid form by process of freezing and water or solvents contained in the freezed material transforms directly in to vapor phase up on subsequent application of vacuum to freezed material , these vapors are then removed from air above the freezed material ,and finally at the end of process we get a material free from water and other solvent without using heat process and without affecting stability of drug .
Freez drying lyophilisation theory explanation:
All matter has three physical states 1) Liquid 2) solid 3) Vapour , application of heat to solid phase transforms it in to liquid phase and further it can be transformed to vapour phase by application of heat to liquid phase.
There exist a point at a particular temperature and pressure where water or solvents exist in all of their physical states of 1) Solid 2)liquid 3)vapor in equilibrium with all of its physical states .
For example water at 273.16 K (0.01 °C) and at vapor pressure of 611.73 pascals comes at a point of equilibrium with all of its physical states 1) Liquid 2) solid 3) Vapor and slight alteration in temperature (lowering) and slight decrease in vapor pressure or increase in vacuum over it transforms water which is solid state directly in to vapor directly without first going to liquid state.
Lyophilisation process is carried our in following stages:
1) Pretreatment of drug:
Treatment with antimicrobial preservative , and stabilizing agents , and addition of solvents to reduce vapor pressure.
2) Freezing : Freezing material below its triple point
3) Drying : Applying vacuum or reducing vapor pressure which brings material to near triple point the process can be repeated depending up on the requirement.
Sterile drugs are prepared with process of freez drying / lyophilisation as follow:
1) Add drug and preservatives excipients in a sterile water for injection (WFI) and dissolve in (WFI).
2) Filter above solution aseptically through bacteria retentive filter of pore size 0.22 micron. This process is also known as sterilization by filtration.
3) Aseptically fill the sterile filtrate in sterile containers and stopper them partially to facilitate removal of sublimate water under aseptic conditions during freeze drying.
4) Aseptically place above filled and partially closed containers of drug product in to lyophilizer.
5) Freeze the load to below triple point.
6) Application of vacuum and heating to evaporate sublimated water.
7) Close vials by stoppering completely in the lyophilizers.
What are advantages of lyophilization?
1)Liquids are processed with ease in aseptic processing
2) Stability of drug is increased as water is completely removed and drug is transformed in to dry powder.
3) Water can be removed completely without excessive heating, which other wise reduce the stability of drug.
4) Drug get easily dissolved when reconstituted.
Which are disadvantages of lyophilization ?
1) Processing time is usually very high
2) In case of sterile drug, it requires sterile water for injection to be supplied separately along with dosage vial for reconstitution
3) Increased handling and processing time
4) Special equipment is required.
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