AEROSOLS
A self-pressurized packaging form, consisting of a metal, glass or plastic container with a permanently attached continuous or metering valve, and designed to dispense products as sprays, streams, gels, foams, lotions or gases. Approximately 90% of aerosol cans are tinplated steel and 10% aluminium.Aerosol is a suspension of fine solid particles or liquid droplets in a pressurized gas . Suspension aerosols delivering the drug in to the respiratory tract must have particle size in the range of 1-5µ and no particle should be larger than 10µm. Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used with a can or bottle that contains a liquid under pressure. When the container’s valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist . As gas expands to drive out the payload, some propellant evaporates inside the can to maintain an even pressure. Outside the can, the droplets of propellant evaporate rapidly, leaving the payload suspended as very fine particles or droplets. Typical liquids
dispensed in this way are insecticides , deodorants and paints . An atomizer is a similar device that is pressurized by a hand-operated pump rather than by stored gas. Usually the gas is the vapor of a liquid with boiling point slightly lower than room temperature . This means that inside the pressurized can, the vapor can exist in equilibrium with its bulk liquid at a pressure that is higher than atmospheric pressure (and able to expel the payload), but not dangerously high. As gas escapes, it is immediately replaced by evaporating liquid. Since the propellant exists in liquid form in the can, it should be miscible with the payload or dissolved in the payload.Chlorofluorocarbons chlorofluorocarbon (CFC) is an organic compound that contains carbon , chlorine , and fluorine have been replaced in nearly every country due to the negative effects CFCs have on Earth’s ozone layer . The most common replacements are mixtures of volatile hydrocarbons, typically propane, n-butane and isobutane. Dimethyl ether (DME) and methyl ethyl ether are also used. All these have the disadvantage of being flammable. Nitrous oxide and carbon dioxide are also used as propellants to deliver foodstuffs (for example, whipped cream and cooking spray). Medicinal aerosols such as asthma inhalers use hydrofluoroalkanes (HFA): either HFA 134a (1,1,1,2,-tetrafluoroethane) or HFA 227 (1,1,1,2,3,3,3-heptafluoropropane) or combinations of the two.
Components of aerosols:
a. Propellants: either liquefied gas or compressed gas
b. Containers: Generally tinplated steel and aluminium
c. Dip tube: Polyethane and polypropylene
d. Valve and actuator: Valve contains ferrule or mounting cap, valve body, dip tube, metering valves.Ferrule joins the valve properly to container.
Valve body has opening for attachment of dip tube. It contains a vapor tab which will produce fine particles size, prevent clogging of valveActuator (Specific designed buttons): produce proper and desire discharge of aerosol product. So they can spray
actuator, foam and solid stream actuators, RADS (Reservoir aerosol type delivery system) and special actuator for metered dose.
Propellant: are called as heart of the aerosols. They can be either liquefied gas or compressed gas.• The liquefied gas includes chlorofluorohydrocarbons (CFC), hydrocarbons, hydro fluorocarbons, hydrocarbons ether, etc.
• The compressed gas can be water immiscible (like argon, nitrogen) or can be water miscible (like CO2 , NO2).
Nomenclature of CFC
Naming consists of 3 digits which is read from right to left. If starting digit is zero then naming is in 2 digits.
1. First digits shows no. of fluorine atoms
2. Second digit show no. of hydrogen atoms + 1 or one more hydrogen then the actual no. of hydrogens
3. Third digit shows carbon atom – 1 or one carbon atom less than the actual no. of carbonsThe remaining valency of carbon is filled with chlorine.
e.g. 011 (have one fluorine, no hydrogen and one carbon)
So the structure of propellant CFC is CFCL3Most widely used CFCs are Trichlorofluoromethane (011), Dichlorodifluoromethane (012), and
Dichlorotetrafluroethane.The major disadvantage of CFCs is that they can cause ozone depletion. The best replacement is volatile
hydrocarbons like propane, butane with environmental acceptability and cheaper.
1. They have better solubility, lighter than water so remain on the top of layer.
2. Pressure is maintained even a single drop of left in the container.
3. Not subjected to hydrolysis but can react with halogen in adverse conditions.
4. But they are inflammable.
Aerosols systems:
1. Two phase system: Propellant or its mixture + active ingredient which is soluble in solvent which is soluble propellant or directly in propellant constitutes 1st phase and 2nd phase is vapor phase or vapours of propellant.
Generally 5% propellant for foams, 95 % propellant for inhalations pdts is used.
To prevent the settling of dispensing particles in suspension oleic acid is used as suspending agent to prevent agglomeration because it can cause clogging of valve and resulting in error in dose administration.
2. Three phase system: for topical aerosols. In which active ingredients are not soluble in propellants so other solvent is used constitutes 1st phase , this solution is immiscible with liquid propellant (2nd phase) and 3rd phase is vapor phase. Water based aerosols involves three phase systems.
Foam dispensing aerosols: uses CO2 and N2O
Manufacture of aerosol:
a. Cold filling: low temperature range – 34 to – 40 0C. But it is not suitable for aqueous pdts and temperate sensitive preparations.
b. Pressure filling: used for all types of aerosols.
Quality control test for pharmaceutical aerosols
1. Flame projection test and Flash point test (using Stel Tagopen Cup apparatus): for flammability and combustibility
2. Particle size determination: Cascade Impactor, Light scattering decay
3. Identification of propellants: By gas chromatography and IR
4. Foam stability: visual evaluations and time for a mass to penetrate the foam by rotational viscometer.
5. Dosage with metered valve: fro reproducibility of dosage each time the valve is suppressed.
6. Vapor pressure: measured by pressure gauge
7. Density: measured by pycnometer or hydrometer
8. Moisture content: measured by Karl-fisher method
9. Performance: is measured by aerosol valve discharge rate
