Definition of Propellants:
- Propellants are the driving force behind aerosol delivery.
- They expel the drug and disperse it as a fine mist or foam.
Types of Propellants:
-
Liquefied Gas Propellant:
- Examples: Chlorofluorocarbons (CFCs), Hydrofluorocarbons (HFCs), Hydrocarbons.
- Characteristics: These exist in equilibrium between liquid and gas phases inside the container.
- Advantages: Provide constant pressure.
-
Compressed Gas Propellant:
- Examples: Nitrogen (N₂), Carbon Dioxide (CO₂), Nitrous Oxide (N₂O).
- Characteristics: Stored as compressed gas in the container.
- Limitations: Pressure decreases as the product is used.
Selection Criteria:
- Safety (non-toxic, non-flammable).
- Environmental considerations (avoiding CFCs due to ozone depletion).
- Compatibility with the formulation.
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Desirable Properties:
- Chemically inert, non-reactive with the drug or container.
- Non-toxic and non-irritating.
- Acceptable vapor pressure under normal storage conditions.
- Stable over the product’s shelf life.
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