1.1) Definition of Aerosol 1, 2, 4, 9, 11
An Aerosol is defined as "An aerosol is a disperse phase system, in which very fine solid drug particles or liquid droplets get dispersed in the propellants (gas), which acts as continuous phase". Or "An Aerosol system which expels the contents from the container that depends on the pressure development by compressed or liquefied gas" Or "An aerosol is a pressurized dosage forms containing one or more therapeutic active ingredients which upon actuation emit a fine dispersion of liquid and/or solid materials in a gaseous medium contain smaller than 50 um".
(Dispersed Phase -Solid / Liquid and Continuous phase - Gas /Propellants)
An Aerosol also called as Pressurized Packages, Pressure Package or Pressurized dosage forms.
The term pressurized package is generally used when referring to the aerosol container or completed product. Pressure is developed to the aerosol system through the use of one or more liquefied or gaseous propellants.
1.2) Advantages of Aerosol 1, 2, 3, 4
- Required quantity of contents can be easily withdrawn from the package without contamination or exposure of the remaining material.
- Aerosols are easy and convenient to apply and can be administered without the help of others.
- The onset of action is faster compared to other dosage forms because the medicament is directly applied to the affected area /part.
- The dispersion of medicament is very good.
- Due to closed packing of aerosols, there is no manual/ direct contact with the medicament.
- Aerosol form can avoid decomposition or inactivation of drug by the pH or enzymatic action of the stomach or intestine and also can avoid the first pass metabolism.
- A specific amount of dose or drug can be removed from the container without contamination of remaining contents.
- Stability can be enhanced for those substances adversely affected by atmospheric oxygen or moisture. (Hydrolysis of medicament can be prevented since propellants do not contain any water. Oxidation is prevented as no air is present in the container)
- Sterility can be for sterile product, because no microorganism can enter even when the valve is opened.
- Metered valve can release the contents in Controlled and Uniformly.
- The aerosol containers protect the photosensitive medicaments. (Except clear glass containers)
- For Inhalation purpose a fine mist of the drug is produced.
- The rapid volatilization of the propellant provides a cooling, refreshing effect.
- Formulation of aerosol and maintaining valve control, the physical form and the particle size of the emitted product may be controlled, which may provides efficacy of a drug.
- Irritation can be reduced by application of topical aerosol medication in a uniform thin layer to the skin without touching the affected area.
Disadvantages of Aerosols
- Aerosols are cost effective.
- Disposal of empty aerosol containers are difficult.
- Due to volatility of the propellant/s can irritate the injured skin.
- Some persons may be sensitive to the propellant/s and persons who using an inhalation aerosol/s, the fluorinated hydrocarbons may cause carcinotoxic effects on rapid and repeated use of the aerosol product.
- Aerosol packs must away from temperature and fire, because it may develop high pressure inside the container leads to explosion.
- If the drug is not soluble in the propellant, aerosol the formulation is difficult.
- Sometimes propellants may cause toxic reactions, if therapy is continued for a long period of time.
1.3) Principle / Mechanism and working of Aerosols 1, 5
In Aerosol, liquefied gas propellant / propellant mixture and product concentrate is sealed within an aerosol container, equilibrium is quickly established between the portion of propellant that remains liquefied and that propellant which vaporizes and occupies the upper portion of the aerosol container.
So, the vapour phase which develops pressure in container, against the walls of the container. At valve assembly and the surface of the liquid phase, this contains the liquefied gas and the product concentrate. This pressure is responsible for actuation of the aerosol valve forces the liquid phase up to the dip tube and through the orifice of the valve contents will released into the atmosphere.
As the propellant/s released in to the air, it expands and evaporates because of the drop down in pressure, which leaves the product concentrate as airborne liquid droplets or dry particles depending upon the formulation type at applied area.
Upon activation of the valve assembly of the aerosol system, the pressure exerted by the propellant/s forces the contents of the package to outside through the opening of the aerosol valve. The physical form of the contents emitted which depends on the formulation type of the product and the type of valve used. Generally, aerosol products designed as to expel their contents in the form of a fine mist, a coarse, wet, or dry spray; a steady stream; or stable or fast breaking foam.
Some portion of the liquid phase released from the container, equilibrium develops between the propellant/s of remaining contents and thus the vapour state is reestablished.
So even during expulsion of the product from the aerosol the pressure within the container remains constant and the product may be continuously released at same rate and with the same proportion.
When the liquid reservoir is completed, the pressure cannot be maintained, and the gas may be expelled from the container with diminishing pressure until it is exhausted.