1) Types of Aerosol System 1, 3, 14, 15, 16
3.1) Solution system / Two Phase system
3.2) Water based system / Two components or Three components system
3.3) Suspension / Dispersion system
3.4) Foam system / Emulsion systems
3.5) Aqueous stable foams
3.6) Non-Aqueous stable foams
3.7) Quick Breaking foams
3.8) Thermal Foams
3.9) Intra Nasal Aerosols
3.10) Compressed Gas Systems
3.1) Solution system / Two Phase system: (Vapour + Liquid phase)
The two phase / solution system is comprised of the liquid phase containing the liquefied propellant/s, product concentrate and the vapour phase.
- Large numbers of aerosol products are available in this system.
- This type of system employed when the product is soluble in the propellant or no other solvent required to dissolve the solid or liquid which using for formulation.
- Depending upon type of spray required, the propellant may consists of propellant 12 or A-70 (for very fine particles) or mixture of propellant 12.
- Lowering of vapour pressure also produce through the addition of less volatile solvents such as ethyl alcohol, propylene glycol, ethyl acetate glycerin and acetone.
- The amount of propellant may vary from 5% (foams) to 95% (Inhalation products).
- Containers- Metal for Oral /inhalation aerosols, Stainless steel, Aluminum, Glass for Inhalation or Local activity at RTI and Plastic coated glass bottle for Topical aerosols.
3.2) Water based system / Two components or Three components system:
(Propellant + Water + Vapour phase)
- Large amount of water can be used to replace all or part of the non aqueous solvents used in aerosols.
- This system is composed of a layer of water immiscible liquid propellant, highly aqueous product concentrate and the vapour phase.This type of system employed when the product is immiscible with the propellant.
- This system emits the contents as spray or foam. Spray is dispersion of active ingredient and other solvents in an emulsion system, in this emulsion system propellant as external phase.
- In this way, when the product is dispensed, the propellant vaporizes and dispersed the active ingredient in minute particles. Due to immiscibility of the water and propellant, it forms a three phase aerosol.
- Ethanol used as a cosolvent to solubilize propellant in the water.
- Surfactant used for the preparation of homogeneous dispersion. Ester forms between the glycol, glycerol and poly hydroxylic acids (oleic, palmitic stearic acids) can be used as surfactants. The surfactants composition can be between 0.5 to 2.0 and propellant composition from 25 to 60%.
- The recent advancement in water based system is the aquasol valve. In aquasol valve the drug is dissolved in the water or the mixture of water and alcohol. The propellant layer is exists on the top water layer. The solubility of the propellant is increases as the amount of alcohol increases and it will become completely soluble (if only alcohol is present). In aquasol, the vaporized propellant and product concentrate will reach to different ducts finally to the actuator. Finally this gives an uniform spray.
- Water based systems produces in dried spray.
3.3) Suspension / Dispersion system:
- When the substances are immiscible or problems due to usage of cosolvents this type of systems formulated.
- In dispersion system, in the propellant or the mixture of propellants, the drug particles are suspended.
- To reduce settling rate surfactants, suspending agents and lubricants added in 0.01 - 1% concentration.
To increase the physical stability of aerosol dispersion:
1. Moisture content must be controlled.
2. The particles should have less solubility with propellant.
3. Use of Dispersing/ suspending agents.
4. By decreasing the density difference between propellant and suspending agent.
5. The particle size should be maintained less than 5 u.
- Sometimes for certain substances agglomerates may form, if the number of agglomerates increases leads to caking.
- As the temperature increases caking will increase. At extreme conditions, the particles will get attached to the walls of container. As moisture content increase agglomeration rate also increase.
- Agglomeration may result due to clogging of valve, may result in inaccuracy in dose and damage to the liner of metal container.
3.4) Foam system / Emulsion systems:
- Emulsion or foam aerosols consist of Active ingredient + Aqueous or Non aqueous vehicle + Surfactant + and propellant (Hydrocarbon or compressed gases).
- Here the propellant which is present in the liquid acts as internal phase.
- These aerosols dispensed as stable aqueous or nonaqueous or quick breaking foam aerosol.
3.5) Aqueous stable foams:
- This system consists of propellant in the range of 8 to 10% v/v. As the concentration of A-70, A-46 propellant increases, it results in stiff and drier spray. And wetter spray is produced as the concentration of propellant decreases.
- Both Hydrocarbon and Compressed gases used as propellants.
- This is generally used for steroids and antibiotics.
3.6) Non-Aqueous stable foams:
- These nonaqueous stable foams of aerosols are formulated with the use of different glycols like PEG and esters of glycols (propylene glycol monostearate) as emulsifying agents.
3.7) Quick Breaking foams:
- Here propellant is the external phase. When dispensed the product will emitted as foam which soon collapses or merges in to liquid.
- Hence, this type of system can be applied to small area or larger surface topical medication without mechanical application.
- Here Cationic or anionic or non-ionic types of surfactants are used in the formulation. It should soluble in both alcohol and water.
- This is pressurized by mixing of 90% concentrate and 10% propellant.
3.8) Thermal Foams:
- These are not using these days. Generally thermal foams used when the warmness is required.
- To produce warm foam for shaving.
- Not readily accepted by the consumer, so discontinued due to expense and lack of effectiveness.
3.9) Intra Nasal Aerosols:
- Drug delivery systems intended for the deposition of medication into the nasal pathways for effectiveness to produce local or systemic effect.
- Intranasal preparations limited to nasal drops, nonpressurized nasal sprays (mists), inhalants and intranasal gels (jellies), ointments and creams. A new alternative is Pressurized metered nasal aerosol.
- The design of the adaptor varies from the inhalation aerosols. To produce smaller particles, the adaptors will be of less height and narrow.
- These are free from contamination, very less quantity of drug moves into the lungs, the mucosal irritation will be reduced.