Chapter 7 Freeze Drying of Pharmaceuticals

7.1 Basic issues for pharmaceutical freeze-drying

• 7.1.1 New Dosage forms of pharmaceutical drugs

• According to its development, pharmaceutical dosage form can be divided into the following generations：– The first generation : simple ointment, pill and powder for oral admini

stration and external use.– The second generation: the tablets, injections, capsules and aerosol

s made by mechanical and automatic machines.– The third generation: slow-release or controlled-release dosage form

s that form a new drug delivery system (DDS) .– The fourth generation:targeted dosage forms that form a targeted dr

ug delivery system.– The fifth generation: the automatic release dosage forms inside the

body when the patients have a serious illness.

• At present, the third and fourth generations of dosage forms are most concerned by scientists.

• In order to realize these new drug delivery system, many new techniques are developed in the formulation of dosage form, such as – solid dispersion, – inclusion, – emulsion,– liposomes, – microencapsulation.

7.1.2 Biological drugs

1. Definition and classification of Biological drugs

• Drugs can be divided into three categories: – chemical drugs (or synthetic drugs); – biological drugs;

• are bioactivative preparations that are made from a living organism, parasites, animal toxins or their products and are used in the prevention, diagnosis, or treatment of cancer and other diseases.

– natural drugs (Chinese medicine)

• Biological drugs include – antibodies, interleukins, and vaccines.

• Biological drugs can be classified according to – the raw materials, biological or separation technology,

or their clinical use.

• According to biological technology, biological drugs can be divided into four categories– Drugs produced by fermentation methods.

• Drugs are produced by microbial metabolism, • including antibiotics, vitamins, organic acids, coenzymes, en

zyme inhibitors, hormone, immunomodifier, as well as other physiologically active substances.

– Drugs produced by genetic methods. • Protein and polypeptide-type drugs are produced by recombi

nant DNA, • including interferon, insulin, interleukin-2 and so on.

– Drugs produced by cell engineering. • Drugs are produced by cell culture of botanical and

zoic cells, • such as human physiological active factors, vaccin

e, monoclonal antibody, and so on;

– Drugs produced by enzyme engineering. • They include medicinal enzyme and drugs which pr

oduced by enzyme or cells immobilization, • such as protease, urgency enzyme, L-asparaginas

e, vitamin C, and so on.

2. Characteristics of biological drugs

• Biological drugs have some distinct characteristics:– The components are too complex to be measured acc

urately. – Because the drugs are composed by a variety of prot

ein that is active, they are affected by temperature.• They are unstable and susceptible to denaturation and deacti

vation.• The changes of parameters in production process have great

influence on the quality of products .

– they are susceptible to been polluted and destructed by microorganism.

7.1.3 Basic process of biological drugs freeze-drying

• The technical procedures of drug freeze-drying consist of four processes: – preparation and freezing, – primary drying (sublimation drying),– secondary drying (desorption drying) – package.

• The temperature, vacuum for each process have to be controlled precisely.

• The freeze-dried drugs are dry and porous solids.– They can be stored in room temperature or in refriger

ator for a long time.

• 1. Preparation and freezing of drugs– In order to form a stable porous structure after freeze drying, the

concentration of drug solution must be a specific value. – Excipients should be added into the low dose thermal sensitive d

rugs (hormone, enzyme, vaccine) to reinforce the structure of freeze-dried products.

– Lyoprotectant should be added into the biological protein-type drugs or slow-release drugs with bio-membrane to protect proteins from denaturation and the bio-membrane from damage.

– The end temperature of pre-freezing must be lower than the glass transition temperature (Tg) or eutectic temperature (Te) of the drug solution.

• 2. Primary drying (sublimation drying)– are performed at low temperature and vacuum. – The drying progresses gradually from the surface to the c

enter of the products. – The pores or channels formed by the sublimation ice bec

ome the ways of vapor to escape.– The boundary between drying layer and frozen layer is k

nown as the sublimation interface.– The temperature of the sublimation interface is a critical

parameter to be controlled in primary drying process. – 90% water in drugs is removed after primary drying. – In primary drying process, the temperature of frozen laye

r must be lower than Te or Tg’. – The temperature of dried layer must is lower than the coll

apse temperature (Tc).– The temperature of the heater in the drying chamber sho

uld be controlled strictly.

• 3. Secondary drying (desorption drying)– purpose : to remove a portion of the bound water.

• The moisture content of drugs is lower than 3% after secondary drying.

– Because of large absorption energy, the product temperature in secondary drying must be increased high enough to remove the bound water, and on the other hand, this temperature cannot induce denaturation of proteins and deterioration of biological drugs.

• The Tg of the products increases gradually with the decrement of water in secondary process.

• So the drying temperature of the products can be increased gradually, but cannot be higher than Tg.

• 4. Encapsulation process– When the secondary drying process is complete,

plugging system in the chamber is used directly to plug the vials in order to prevent the freeze dried drugs from oxidation and water absorption.

– The encapsulation can also be completed after filling nitrogen gas into the chamber.

7.1.4 Characteristics of freeze-drying technology for drugs • characteristics of freeze-drying technology

for drugs are – can prevent the active components in from denaturati

on or loss of biological activity.– can protect the components in drugs from oxidation.– can greatly reduce the loss of volatile components in

drugs.– can inhibit the growth of microorganism and the activit

y of enzyme in drugs.

– Freeze dried drugs will maintain the original structure.– Freeze dried drugs have good rehydration property.– Freeze dried drugs can be stored at room temperatur

e for a long time– The initial cost of freeze-drying equipment is larger. Fr

eeze drying is a time and energy consuming process.– It is very difficult to control the parameters at optimum

level.

7.1.5 Critical problems of freeze-drying in drugs

• 1. Temperature Control and identification of drying procedures– Frozen drugs will melt, collapse or crimple if the temperatur

e is higher than the optimum temperature.

– if the temperature is too low, refrigeration load will causing excessive energy consumption and the sublimation rate will

be decreased greatly

• 2. Cooling Rate in freezing process – freezing process determines the drying rate a

nd the quality of freeze-dried product. – The optimum cooling rates vary with different

biological agents.For instance, • slow freezing is usually beneficial to protein polype

ptide-type drugs. • Fast freezing is usually beneficial to the virus and v

accine.

• 3. Types and concentration of lyoprotectant– The molecular structure of the active components

is different for different biological agents.– The types and concentration of lyoprotectants req

uired in freeze drying are also different. – Up to now, there is not a universal lyoprotectant a

pplied to all of the biological agents.

7.2 Freeze-drying of Protein and Hormone • Bio-protein-type drugs

– are typical products of modern bioengineering preparation.

– easy to be polymerized in liquid state because they are thermal sensitive.

– easy to be contaminated microorganism and oxidized when exposed in air.

– Freeze drying is an effective technique for the storage of bio-protein-type drugs.

7.2.1 Freeze-drying of enzyme

• Almost all enzymes are proteins that catalyze chemical

reactions • Example: Cu/Zn SOD

7.2.2 Interleukin

• Cytokine or growth factors are polypeptides used to regulate cellular proliferation and differentiation.

• Cytokine related to immunization is called interleukin• Example:

7.3 Freeze drying of fibrinogen

• 7.3.1 Fibrin Glue (also called fibrin sealant, FS) – The properties of fibrin glue (also called fibrin sealant, FS) are b

etter than any other biological or synthetic surgical hemostat in aspect of histocompatibility, nontoxicity and clinical efficacy.

7.3.2 Fibrinogen

• Fibrinogen is one of the two components of fibrin glue • In clinic the freeze-dried fibrinogen are required to rehydr

ate fast and to be stable in storage.

• Fibrinogen is a water-soluble active protein. It is unstable

in liquid state, easily deteriorated by oxidation.

7.3.3 The freeze-drying of fibrinogen

• 1. Fibrinogen preparation– Plasma Preparation

– Extraction of fibrinogen • 2. The temperature protocol for the freeze-drying of fibrin

ogen – Example:Freeze-dryer (Lyo-7.5)

• Thermocouples are placed inside the vials on the tray as shown in Fig.7-3

• 3. Lyoprotectant for the freeze-drying of Fibrinogen • Sucrose, glycine and mannitol are combined to formulate the

lyoprotectant.

• 4. The rehydration property and stability of freeze dried fibrinogen

• see Table 7-1.

• The end