❖ Aerosol & Its Types
❖ Advantage & Disadvantage
❖ Metered Dose Inhalers
❖ Manufacture of Aerosol
❖ Quality Control Tests
❖ Drug Delivery to The Lungs
❖ Mechanism & factors affecting
deposition of drugs
Definition of Aerosol
▪ “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”.
▪ Pharmaceutical aerosols are products that are packaged under pressure and contain therapeutically
active ingredients that are released upon activation of an appropriate valve system.
▪ They are intended for topical application to the skin as well as local application into the nose (nasal
aerosols), mouth (lingual aerosols), or lungs (inhalation aerosols).
Types of Aerosols
Aerosols consist of
• Two-phase (gas and liquid)
• Three-phase (gas, liquid, and solid or liquid) systems.
The two-phase aerosol
• It consists of a solution of active ingredients in liquefied propellant or in the vaporized propellant.
• The solvent is composed of the propellant or a mixture of the propellant.
• Co-solvents such as alcohol, propylene glycol, and polyethylene glycols, which are often used to
enhance the solubility of the active ingredients.
• It consist of a suspension or emulsion of the active ingredient(s) in addition to the vaporized
• Suspension consists of the active ingredients that may be dispersed in the propellant system with
the aid of suitable excipients such as wetting agents and/or solid carriers such as talc or colloidal
1. Space sprays: These are finely divided sprays having particle size upto 50 m. e.g. insecticides,
disinfectants and room deodorizers.
2. Surface coats: These are also sprays but disperse particles are coarse with size up to 200 m. They
produce a wet coat when sprayed on a surface. e.g. hair sprays, personal deodorant, powder sprays
and topical medicament sprays.
3. Foam: These are produced by rapid expansion of propellants through an emulsion. Hence, the
product comes out in the form of a foam or froth. e.g. shaving cream and vaginal product.
Advantages of aerosols
▪ Ease of use
▪ Protection from contamination with foreign materials since the product is sealed inside the
▪ Protection from the effect of air and moisture.
▪ Regulation of dosage by the use metered dose valve.
▪ Easily withdrawn of drug and convenient to apply.
▪ Faster onset of action.
▪ No manual/ direct contact with the medicament.
▪ Avoid the first pass metabolism.
▪ A specific amount of dose or drug can be removed.
▪ No microorganism can enter.
▪ Release the contents in Controlled and Uniformly.
▪ Provides efficacy of a drug.
▪ Irritation can be reduced.
Disadvantages of aerosols
▪ Difficult disposal of empty aerosol containers.
▪ Allergic in some cases.
▪ Some formulation is difficult.
▪ Sometimes propellants may cause toxic reactions
▪ Aerosol packs are must not be subjected to heat since high pressures can develop most
pharmaceuticals should not be exposed to heat in any case.
▪ Toxicity of propellants.
▪ Catalytic oxidation of drugs such as ascorbic acid and epinephrine has been caused by traces of
metal from valve parts of container.
Components of Aerosols
Components of Aerosol Package are
3. valve, and actuator
4. product concentrate (concentrate containing the active ingredients)
The nature of these components determines such characteristics as particle size distribution,
uniformity of dose for metered valves, delivery rate, wetness and temperature of the spray, spray
pattern and velocity or plume geometry, foam density, and fluid viscosity.
• A propellant is a material that is used to move (“Propel") an object. The material is usually
expelled by gas pressure through a nozzle. The pressure may be from a compressed gas, or a gas
produced by a chemical reaction. The exhaust material may be a gas, liquid, plasma, or, before the
chemical reaction, a solid, liquid or gelled.
• The propellant supplies the necessary pressure within an aerosol system to expel material from the
container and, in combination with other components, to convert the material into the desired
• Common chemical propellants consist of a fuel; like gasoline, jet fuel, rocket fuel, and an oxidizer.
• In aerosol spray cans, the propellant is simply a pressurized gas in equilibrium with its liquid. As
some gas escapes to expel the payload, more liquid evaporates, maintaining an even pressure.
Types of Propellants
(a) Liquefied gases Propellants
(b) Compressed gases Propellants
Depending on the route of administration and use,
I) Type-I Propellant A- Liquefied Gas
1) For oral and inhalation (Fluorinated hydrocarbons)
• Tri-chloro-mono-fluoro methane (propellant 11)
• Di-chloro di-fluoro methane (propellant 12)
2) Topical Pharmaceutical aerosols (Hydrocarbons)
II) Type-II Propellant B - Compressed Gas Propellants
1) Compound gases
• Carbon di-oxide
Liquefied propellants are gases that exist as liquids under pressure. Because the
aerosol is under pressure the propellant exists mainly as a liquid, but it will also be in
the headspace as a gas. As the product is used up as the valve is opened, some of the
liquid propellant turns to gas and keeps the head space full of gas. In this way the
pressure in the can remains essentially constant and the spray performance is
maintained throughout the life of the aerosol. The propellant is an essential element in
Can be used for water based aerosols and topical use.
• Excellent solvents
• It does not cause ozone depletion
• Stability & Purity
• Wide range of Boiling Points
• Wide range of Vapor Pressure
• Low Toxicity
• Unknown toxicity produced
1. Propane - Propellant A-108
2. Isobutane - Propellant A-31
3. Butane - Propellant A-17
Chloro Fluoro Carbons
• Chemical inertness
• Lack of toxicity
• Non flammability.
• Lack of explosiveness.
• Propellant of choice for oral and inhalation .
• High cost
• It depletes the ozone layer
1. Trichloromonofluoromethane - Propellant 11
2. Dichlorodifluoromethane - Propellant 12
3. Dichlorotetrafluoroethane - Propellant 114
Compressed gas propellants really only occupy the headspace above the
liquid in the can. When the aerosol valve is opened the gas 'pushes' the liquid
out of the can. The amount of gas in the headspace remains the same but it has
more space, and as a result the pressure will drop during the life of the can.
Spray performance is maintained however by careful choice of the aerosol
valve and actuator.
Carbon dioxide, Nitrous oxide and Nitrogen
Used when the aqueous phase need not be miscible with the propellant.
Do not have chilling effect, for topical preparation .
– Non flammable
– No environmental problems
– Pressure falls during use
– Produce coarse droplet spray
– Require use of non volatile co solvent
They must be able to withstand pressures as high as 140 to 180 psig (pounds per sq. inch gauge) at
130 ° F.
Aerosol container can be divided into four parts:
A . Metals
▪ Tinplated steel
▪ Stainless steel
▪ Uncoated glass
▪ Plastic coated glass
Tin Plated Steel Containers
• It consist of a sheet of steel plate, this sheet is coated with tin by electrolytic process .
• The coated sheet is cut into three pieces ( top , bottom and body) .
• The top, bottom are attached to body by soldering.
• When required it is coated with organic material usually oleoresin, phenolic , vinyl or epoxy
• Welding eliminates soldering process, Saves considerable manufacturing time and decreases
the product/container interaction.
• Recent developments in welding include Soudronic system and Conoweld system.
• Used for inhalation and topical aerosols .
• Manufactured by impact extrusion process.
• Light in weight, less fragile, Less incompatibility due to its seamless nature.
• Greater resistance to corrosion .
• Pure water and pure ethanol cause corrosion to all containers.
• Added resistance can be obtained by coating inside of the container with organic
coating like phenolic , vinyl or
epoxy and polyamide resins.
Stainless Steel Containers
Used for inhalation aerosols
• Extremely Strong.
• Resistant to many materials.
• No need for internal coating.
These containers are preferred because of its Aesthetic value and absence of incompatibilities.
• These containers are limited to the products having a lower pressure (33 psig) and lower
percentage of the propellant.
• Used for topical and MDI aerosols.
Two types of glass aerosol containers
i) Uncoated glass container:
Less cost and high clarity and contents can be viewed at all times.
ii) Plastic coated glass containers:
These are protected by plastic coating that prevents the glass from shattering in the event of
• Easy to open and close .
• Capable of delivering the content in the desired form such as spray, foam, solid stream etc.
• It can deliver a given amount of medicament .
TYPES OF VALVES :
1.Continuous spray valve
Continuous Spray Valve
Used for topical aerosols .
Valves assembly consists :
• Ferrule or mounting cup
• Valve body or housing
• Dip tube
FERRULE OR MOUNTING CUP :
• Used to attach valve to container.
• Made from Tin plated steel, Al , Brass .
• Under side of the valve cup is coated with single or double epoxy or vinyl resins.
VALVE BODY OR HOUSING :
• Made up of Nylon or Derlin and contains a opening at the point of attachment of dip tube. (0.013 to
• Made from Nylon or Derlin , brass and stainless steel can also be used. (orifice - 0.013 to 0.030
• Made from Buna-N and neoprene rubber.
• Made from Stainless steel .
• Used to hold gasket in place.
DIP TUBE :
• Made from Poly ethylene or poly propylene.
• Inner diameter 0.120 – 0.125 inch.
• However for Capillary dip tube inner diameter is 0.050 inch and for highly viscous products it is
0.195 inch. 24
• Used for dispensing of potent medication.
• Operates on the principle of a chamber whose size determines the amount of medication
• Approximately 50 to 150 mg ±10 % of liquid materials can be dispensed at one time with
the use of such valve.
• These are specially designed buttons which helps in delivering the drug in desired form i.e., spray,
wet stream, foam or solid stream .
TYPES OF ACTUATORS :
• Spray actuators
• Foam actuators
• Solid steam actuators
• Special actuators
• It can be used for topical preparation, such as antiseptics, local anesthetics and spray on
• It allows the stream of product concentrate and propellant to pass through various
openings and dispense as spray.
FOAM ACTUATORS :
• It consist of large orifice which ranges from 0.070—0.125 inch .
SOLID STREAM ACTUATORS :
• These actuators are required for dispensing semi solid products such as ointments .
SPECIAL ACTUATORS :
• These are used for a specific purpose.
• It delivers the medicament to the appropriate site of action such as throat, nose, dental
and eyes etc.
• The dip tubes are made from polyethylene or polypropylene.
• Dip tube is used for the following purposes:
(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 without dispensing the contents of the package.
• The dip tube should be extended almost to the bottom of the container.
• In case the length of the dip tube is short, the contents of the aerosol container will not come out
• However, if the dip tube is touching the bottom of the container, it will block the passage of
Metered Dose Inhalers
• Used to minimize the number of administration errors.
• To improve the drug delivery of aerosolized particles into the nasal passageways and respiratory
Advantages of MDI:
• It delivers specified amount of dose .
• Portable and compact.
• Quick to use , no contamination of product.
• Dose-dose reproducibility is high.
Disadvantages of MDI :
• Low lung deposition ; high pharyngeal deposition .
• Coordination of MDI actuation and patient inhalation is needed.
Manufacture of Aerosols
• Pressure filling apparatus
• Cold filling apparatus
• Compressed gas filling apparatus
PRESSURE FILLING APPARATUS
• It consists of a pressure burette capable of metering small volumes of liquefied gas into the aerosol
container under pressure.
• Propellant is added through an inlet valve located at the bottom or top of the pressure burette.
• The propellant is allowed to flow with its own vapor pressure in the container through aerosol
• The trapped air escapes out from the upper valve.
• The propellant stops flowing when the pressure of burette and container becomes equal.
• If further propellant is to be added, a hose (rubber pipe) leading to a cylinder of nitrogen is attached
to the upper valve, the pressure exerted by nitrogen helps in the flow of the propellant into the
• Another pressure filling device makes use of piston arrangement and is capable of
maintaining positive pressure .
• This type of device cannot be used for filling inhalation aerosols which have metered valves.
•This method involves filling of the concentrate into the container at the room temperature.
• Then the valve is placed in the container and crimped.
• Through the opening of the valve the propellant are added or it can be added “under the cap”.
• Since the opening of the valve are smaller in size ranging from 0.018-0.030 inches, it limits the
production and the process becomes slow.
• But with the use of rotary filling machines and newer filling heads where the propellants are
filled through valve stem, the production rate is increased.
• The trapped air in the container and air present in head space is removed before filling the
propellant to protect the products from getting adversely affected.
• Various units used in pressure filling line are arranged in the following order :
Unscrambler , Air cleaner , Concentrate filler , Valve placer , Purger ,Valve crimper , Propellant filler
,Water bath , Labeler , Coder and Packing table .
• Purger ,vacuum crimper and pressure filler are replaced with a single unit if filling is carried by
‘under the cap’ method.
ADVANTAGES OF PRESSURE FILLING:
• Solutions, emulsions, suspensions can be filled by this method as chilling does not occur.
• Contamination due to moisture is less.
• High production speed can be achieved.
• Loss of propellant is less.
• Certain types of metering valves can be handled only by the cold filling process or through
use of an under the cap filler and valve crimper.
• Process is slower than Cold filling method. 32
Cold Filling Apparatus
• It consist of an insulated box fitted with copper tubings and the tubings are coiled to increase
the area exposed to cooling.
• The insulated box should be filled with dry ice or acetone prior to use.
• The apparatus can be operated with or without metered valves.
• Hydrocarbon propellant cannot be filled into aerosol containers using this apparatus because
large amount of propellant escapes out and vaporizes.
• This may lead to formation of an explosive mixture .
• Fluorocarbon vapors do not form any explosive or flammable mixture though their vapors are
heavier than air.
• Non aqueous products and products which can withstand low temperatures of - 40°F are
used in this method.
• The product concentrate is chilled to a temperature of - 40°F and filled into already chilled
• Then the chilled propellant is added completely in 1 or 2 stages, depending on the amount.
• Another method is to chill both the product concentrate and propellant in a separate pressure
vessel to - 40 °F and then filling them into the container.
• The valve is placed and crimped on to the container.
• Then test for leakage and strength of container is carried out by passing container into a heated
water bath, where the contents of the container are heated to 130°F. After this, the containers are
air dried , capped and labeled.
Various units used in cold filling methods are :
• Un scrambler, Air cleaner ,Concentrate filler ,Propellant filler ,Valve placer ,Valve crimper ,Water
bath ,Labeler, Coder and Packing table .
• The cold filling method is no longer being used, as it has been replaced by pressure filling method.
• Easy process .
• Aqueous products, emulsions and those products adversely affected by cold temperature cannot be
filled by this method.
COMPRESSED GAS FILLING APPARATUS
• Compressed gases have high pressure hence a pressure reducing valve is required.
• The apparatus consists of delivery gauge.
• A flexible hose pipe which can withstand 150 pounds per square inch gauge pressure is attached to the
delivery gauge along with the filling head.
• A flow indicator is also present in specialized equipments.
• The product concentrate is filled into the container.
• Valve is placed and crimped on the container.
• With the help of vacuum pump the air is removed from the container.
• Filling head is put in the opening of the valve and the valve is depressed and the gas is allowed to flow
in to container.
• The gas stops flowing if the delivery pressure and the pressure within the container become equal.
• Carbon dioxide and nitrous oxide is used if more amount of gas is required.
• High solubility of the gas in the product can be achieved by shaking the container manually or with the
help of mechanical shakers.
Quality control tests
It includes the testing of
2. Valves, Actuators and Dip Tubes
4. Weight Checking
5. Leak Testing
6. Spray Testing
1. PROPELLANTS :
Vapor pressure and density of the propellant are determined and compared with specification sheet.
Parameter Tested By
Identification Gas Chromatography
Purity and acceptability Moisture, Halogen,
Non-Volatile Residue determinations
2. VALVES , ACTUATORS AND DIP TUBES :
• Sampling is done according to standard procedures as found in Military Standards “MIL-STD-105D”.
• For metered dose aerosol valves ,test methods were developed
by‘ Aerosol Specifications Committee’, ‘Industrial Pharmaceutical Technology Section, ‘Academy Of
• The objective of this test is to determine magnitude of valve delivery & degree of uniformity between
• Standard test solutions were proposed to rule out variation in valve delivery.
Ingredients % w/w Test Solutions ‘A’ Test Solutions ‘B’ Test Solutions ‘C’
Isopropyl Myristate 0.10% 0.10% 0.10%
Methane 49.95% 25.0% 50.25%
Ethane 49.95% 25.0% 24.75%
Alcohol USP - 49.9% -
Specific Gravity at
25°c 1.384 1.092 1.388
• Take 25 valves and placed on containers filled with specific test solution.
• Actuator with 0.020 inch orifice is attached.
• Temperature -25±1°C.
• Valve is actuated to fullest extent for 2 sec and weighed.
• Again the valve is actuated for 2 sec and weighed.
• Difference between them represents delivery in mg.
• Repeat this for a total of 2 individual deliveries from each of 25 test units.
Individual delivery wt in mg.
Valve delivery per actuation in μL =
Specific gravity of test solution
Valve Acceptance: Deliveries Limit’s
54μL or less ± 15%
55 to 200 μL ± 10%
Of the 50 individual deliveries,
• If 4 or more are outside the limits : valves are rejected
• If 3 deliveries are outside limits : another 25 valves are tested. Lot is rejected if more than 1 delivery is
outside the specifications.
• If 2 deliveries from 1 valve are beyond limits : another 25 valves are tested. Lot is rejected if more than1
delivery is outside specification. 39
3. CONTAINERS :
• Containers are examined for defects in lining.
• Quality control aspects includes degree of conductivity of electric current as
measure of exposed metals.
• Glass containers examined for Flaws.
4. WEIGHT CHECKING :
• Is done by periodically adding to the filling line tared empty aerosol containers, which after filling with
concentrate are removed & weighed.
• Same procedure is used for checking weight of Propellants being added.
5. LEAK TESTING :
• It is a means of checking crimping of the valve and detect the defective containers due to leakage.
• Is done by measuring the Crimp’s dimension & comparing.
• Final testing of valve closure is done by passing the filled containers through water bath.
6. SPRAY TESTING :
• Most pharmaceutical aerosols are 100% spray tested.
• This serves to clear the dip tube of pure propellant and pure concentrate.
• To check for defects in valves and spray pattern.
Therapeutic activity and Toxicity are considered in Biologic testing.
1. Therapeutic Activity:
For Inhalation Aerosols: The determination of therapeutic activity is dependent on the particle size.
For Topical Aerosols: Therapeutic activity of aerosol products are determined by applying the
therapeutically active ingredients topically to the test areas and the amount of therapeutically active
substances absorbed is determined.
2. Toxicity study:
For Topical Aerosols: The topically administered aerosols are checked for chilling effect or irritation in
the skin. When aerosol are topically applied, thermistor probe attached to the recording thermometer are
used to determine the change in skin temperature for a given period of time.
For Inhalation Aerosols: Inhalation toxicity study is done by exposing test animals to vapours sprayed
from the aerosol container.
Drug Delivery to the Lungs
❏ The respiratory tract is one of the oldest routes used for the administration of drug.
❏ This type of application in the therapy of these diseases is a clear form of targeted drug
❏ Currently, over 25 drug substances are marketed as inhalation aerosol products for local
pulmonary effects & about the same number of drug are in different stages of clinical
❏ The drugs used for asthma & COPD (Chronic Obstructive Pulmonary Disease) e.g. β 2
-agonists such as salbutamol (albuterol) , terbutalin formoterol, corticosteroids such as
sodium cromoglycate or nedocromi.
Mechanism & Factors Affecting Deposition of Drugs
Particle deposition in the airways-
❏ Inertial impaction
❏ Brownian diffusion
Inertial Impaction: Where a bifurcation occurs in the respiratory tract, the air stream
changes direction & particles within the air stream having , high momentum, will impact on
the airway wall rather than follow the changing air stream. (particles >5 μm & particularly >
10 μm deposited)
Gravitational sedimentation: As the remaining small particles move on to the central lung,
the air velocity gradually decreases too much lower valves & the force of gravity becomes
important. (particles 1-5 μm deposited)
Brownian motion: The finest particles enter the periphery of the lung where they can
contact with the walls of the airways as the result of Brownian motion like particle
diffusion. (particles smaller than 0.5 μm deposited)
Physiological factors affecting deposition in airways:
❏ Lung morphology
❏ Inspiratory flow rate
❏ Coordination of aerosol generation with inspiration
❏ Tidal volume
❏ Breath holding
❏ Disease states
Pharmaceutical factors affecting aerosol deposition:
❏ Aerosol velocity
❏ Physical stability
1. Leon lachmen,Herbert A.Lieberman,Joseph L. kanig “the theory and practice of Industrial
pharmacy” third edtion 589-618
2. E.A.raulins “Bentley’s Text book of pharmaceutics” eighth edition 669-684
3. Gilbert S.banker,christopher T.rhodes “Modern pharmaceutics” Third edition 547-554
4. James Swerbrick, James C.Boylon “Encyclopedia of pharmaceutical technology” volume 2
second edition 1735-1752
5. M.E.Aulton “Pharmaceutics the scince of dosage form design” second edition 473-489
6. Philip d Gerbino “Remingtons The science and practice of pharmacy” volume 1 21st edition
7. “The Theory & Practice Of Industrial Pharmacy” by Leon Lachman , H.A.Lieberman.