contents:-Definition, advantages and disadvantages

Classification of aerosolsFormulation of aerosols

Parts of an aerosol containerPackaging of aerosols

Definiton- aerosols may be defined as dispersed phase system in which very fine

solid particles or liquid droplets gets dispersed in the gas which acts as continuous phase . These are also called pressurised dosage form.

Advantages- The medicament can be delivered directly to the affected area such as burnt skin and

wound. So it minimises the discomfort caused by mechanical or manual application.

Absence of air prevents oxidation of the product.

The hydrolysis of medicaments can be prevented

The sterility of the products can be maintained

The application of medicament is easier

Disadvantages- Aerosols are costly preparations

Some of the propellants are very toxic

The cooling effect of highly volatile propellants may cause discomfort on injured skin

Lot of difficulties are faced in aerosol formulation when the drug is not suitable

Classificaton of aerosol:- Aerosols may be classified as:

1)Space sprays: these are finely divided sprays having particle size upto 50micron,e.g. insecticides, disinfectants , and room deodorizers

2)Surface coats: these are also sprays but disperse particles are coarse with sizes upto 200micron. They produce a wet coat when sprayed on a surface e.g. hair sprays, personal deodrants, powder sprays and topical medicament sprays

Foam: these are produced by rapid expansion of propellantsthrough an emulsion. Hence, the product comes out in the form of foam or froth, e.g. shaving cream or vaginal product

Formulation of aerosols: An aerosol formulation basically consists of propellant and the medicaments to be

propelled Propellant – the propellant generally is regarded as the heart of the aerosol package. In

addition the necessary force to expel the product, the propellant must act as a solvent and dileunt and has much to do with the determining the characteristics of the product as it leaves the container. Various chemical compounds have been used as aerosol propellants. compounds useful as propellants can be classified as-

Liquefied gases- they have an advantage that the pressure within the container remains constant, two types of liquefied gases are used:-Chloroflurocarbons(CFC)-finds greater use since they are non-inflammable e.g. propellant 11(trichloromonofluromethane), propellant12(dicholrodifluromethane).

Hydrocarbons(HC)- they are advantageous since they are less expensive than any of the fluorocarbons and generally are environment acceptable.

Hydrochloroflurocarbons(HCFC) Hydroflurocarbons(HFC) Hydrocarbon ethers Compressed gasses

Aerosol maybe of two types:-

Two phase system- this is employed in cases where the product is a solid insoluble in the propellant or it is solid or liquid which dissolve in it. In the first case the solid is suspended in the propellant, so that aerosol system will have one liquid phase and one gaseous phase above it

Three phase system- this system is employed in cases where the product is immiscible with the propellant. The medicaments are dissolved in a liquid which does not mix with the liquefied propellant.

Parts of an aerosol container:- An aerosol container can be divided into four parts-

1)Container- in pharmaceutical aerosol packaging, the containers are made out of metal(such as tin plated steel, aluminum and stainless steel) glass and plastic. These containers can withstand high pressure.

2)Valves- the valves should be such that it can be easily opened and closed. It should also deliver the content in the desired form. So three types of valves are used these nowadays:i)continuous spray valveii)metering valveiii)foam valve

By using continuous spray valve, the medicament is expelled continuously as long as the pressure is applied on the actuator.

But by using metering valve, only a definite quantity of the medicament is expelled when the actuator is pressed.

If the contents of the aerosol are required to come out in the form of a ball of foam, a foam valve is used is used in this case.

3)Actuator- actuator is fitted on the valve stem. It helps in the easy opening and closing of the valve whenever it is required. There are various types of actuators which can produce spray, fine mist or foam.

4)Dip tubes- the dip-tubes are made from polyethylene or polypropylene. Dip tube is used for the following purpose :

i)it conveys the liquid from the bottom of the container to the valve at the top.

ii)It prevents the propellant to come out

Packaging of aerosols:- Cold filling process

Cool the product to -40F

Fill into the cooled container

Cool the propellant

Add the propellant to the product concentrate

Pressure-fill processfill the container with product concentrate

Place the valve in its position by compression

Now introduce the propellant via valve

Applications of aerosol packaging:-1) They are used for spray bandages and for application of drugs meant for topical use.2) They are used for spray administration of drugs into various body cavities.3) The are for administration of drugs such as local anesthetics, local antiseptic, local

analgesics, and anti-inflammatory drugs.4) They are used to spray cosmetics preparations such as perfumes.5) They are used to spray disinfectants, deodorizers and air sanitizers.

Slide presentation by

Anurag Chanda

B.Pharm 5th Semester