Propellents

Copyright © Wondershare SoftwareCopyright © Wondershare Software
ADVANCES IN
PROPELLANTS
Presented By
SUNILBOREDDY
M.Pharmacy (Pharmaceutics)

CONTENTS
 History
 Definition
 Types Of Aerosols
 Applications And Advantages
 Advantages Over Other Dosage Faorms
 Disadvantages Of Aerosol
 Components Of Aerosols
 How An Aerosol Works
 Why Do We Need A Propellant
 Propellant Definition
 Propellant Examples
 Advances In Metered Dose Inhaler Technology
 Ideal PropertiesCompany LogoCompany Logo

 Lyle Goodhue and William Sullivan (United States Department of
Agriculture), who are credited as the inventors of the modern spray can.
 In the first modern day pressurized aerosol form’s was developed in early
1950 and has introduced as Medihaler Epi by Ricker Laboratories.
HISTORY

HISTORY
 Pharmaceutical aerosols have been playing a crucial role in the health and well
being of millions of people throughout the world for many years. These products
include pressurized metered dose inhalers (MDIs), dry powder inhalers (DPIs),
nebulizers, sublinguals, skin sprays (coolants, anesthetics, etc.) and dental
sprays.
 Since the mid 1950s, aerosol forms of pharmaceuticals have played an important
role in treating respiratory illnesses such as asthma and chronic obstructive
pulmonary disease (COPD), and MDIs and DPIs have become an important part of
that treatment.
 Traditionally most pharmaceutical aerosols have been propelled with
chlorofluorocarbons (CFCs), but current global regulations require pharmaceutical
aerosols to be reformulated to contain non-ozone-depleting propellants.

 Alternatives to CFC propellants must satisfy many other criteria in addition to
environmental acceptability. Most importantly, they need to have acceptable toxicity
profiles given their use in the delivery of medicaments. For the sake of patient safety,
it is also important that they are nonflammable. Finally, their physical properties must
allow workable formulations within the available technology.
 The two current alternatives to CFC propellants for pharmaceutical aerosols are
hydrofluorocarbon (HFC) 134a (also known as hydrofluoroalkane (HFA) 134a or
1,1,1,2- tetrafluoroethane), and HFC-227ea (HFA-227ea or 1,1,1,2,3,3,3-
heptafluoropropane)

Of the alternatives identified, the hydrofluoroalkanes (HFAs) or HFCs were targeted
for development as replacements for the CFCs in MDIs. Within this class, 134a and
227ea were adopted for inhalation toxicity testing by two consortia of pharmaceutical
companies: IPACT 1 for 134a and IPACT 2 for 227ea.
(IPACT: International Pharmaceutical Aerosol Consortium for Toxicity Testing)
These programs established the safety profile of both propellants, which has led to the
recommendation by the Committee of Proprietary Medicinal Products (CPMP) of their
suitability for use in MDIs.

NEW CFC SUBSTITUTES FOR
MDIS.
The HFAs are rapidly replacing CFCs in MDIs. Numerous clinical studies
have focused on documenting efficacy and safety. Some data suggest that the
lung deposition fraction of beclomethasone dipropionate using HFA-134a
MDI is much higher than that for CFC MDI. The major reason for this
difference is the particle size of the HFA aerosol, 1.1 mm, compared to
the CFC aerosol, with a size of 3.5 mm. Evidence indicates that pulmonary
deposition can be significantly influenced by HFA chosen and by actuator
design. Lung deposition for fenoterol was significantly influenced by the
actuator nozzle designed for HFA-134a.

AEROSOL CONTAINER

DEFINITION
 An aerosol can be defined as a dispersion of solid and liquid particles suspended in
gas
 Pharmaceutical aerosols or pressurized dosage forms is defined as “ a system that
depends on the power of a compressed or liquefied gas to expel the contents from
the container.”
 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).

HOW AN AEROSOL WORKS
An aerosol contains two essential components:-
The product, in the form of a liquid, emulsion or suspension.
The propellant, which can be a liquefied gas, or even a compressed gas.

The way in which the liquid is turned into a spray depends on a
number of factors which include,
1. The valve specification
2. The actuator specification
3. The type and amount of propellant

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.
Three-phase systems
 It consist of a suspension or emulsion of the active ingredient(s)in addition to
the vaporized propellants.
 suspension consists of the active ingredient's 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 silica.

APPLICATIONS AND
ADVANTAGES Ease of use
 Protection from contamination with foreign materials since the product is
sealed inside the container.
 Protection from the effect of air and moisture.
 Regulation of dosage by the use metered dose valve.
 Economic usage of dosage form metered dose valves are used for
expensive topical preparations which may otherwise be formulated as
ointments, creams or lotions.
 The usage of these latter dosage forms will depend on the users attitude to
economy and often involved some loss of the product on an applicator
 Topical preparations are also well suited for presentation as aerosol or
sprays. The irritation of a sore wound caused by the rubbing in of an
ointment or creams is avoided and cooling effect of aerosols containing
liquefied gases may be advantageous.
 These aerosol products were intended for topical administration for the
treatment of burns, minor cuts, and bruises, infections and various
dermatologic conditions.

ADVANTAGES OVER OTHER DOSAGE
FORMS
 A dose can be removed without contamination of remaining material.
 The medication can be delivered directly to the affected area in a desired form,
such as spray, stream, quick-breaking foam or stable foam.
 Irritation produced by the mechanical application of topical medication is
reduced or eliminated.
 Other advantages are ease and convenience of application and application of
medication in a thin layer.

DISADVANTAGES OF
AEROSOL
 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
1. propellant,
2. container,
3. valve, and actuator
4. product concentrate (concentrate containing the active ingredient's)
 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.

WHAT IS PROPELLANT
 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 physical form.

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.
 Various types of propellants are utilized, while the fluorinated hydrocarbons such as
trichloromonofluromethane (propellant 11), dichlorodifluoromethane (propellant 12), and
dichlorotetrafluroethane (propellant 114) are found to be widespread use in most aerosols for oral
and inhalation use, topical pharmaceutical aerosols utilize hydrocarbons ( propane, butane, and
isobutene) and compressed gases such as nitrogen, carbon dioxide, and nitrous oxide.

WHY DO WE NEED A PROPELLANT
The contents of the aerosol are made up of two components:
1. The product, in the form of a liquid, emulsion or suspension.
2. The propellant, which can be a liquefied gas, or even a compressed gas.
The propellant is the driving force (or, you could say, the ‘ENGINE’), behind the
aerosol.

PROPELLANTS CLASSIFICATION
Propellants may be broadly classified
 LIQUEFIED GASES
 COMPRESSED GASES
 Propellants within this definition include various hydrocarbons, especially
halogenated derivatives of methane, ethane, and propane, low molecular weight
hydrocarbons such as the butanes and pentanes, and compressed gases such as
carbon dioxide, nitrogen, and nitrous oxide.
 Mixtures of propellants are frequently used to obtain desirable pressure,
delivery, and spray characteristics.
 A good propellant system should have the proper vapor pressure characteristics
consistent with the other aerosol components.

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 head space 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
the formulation.
Compressed gas propellants really only occupy the head space 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.

In both of the examples above, you will see that the can is not full to the top with
liquid. This is for safety reasons, as there must always be sufficient space for the
propellant gas to occupy, under all likely storage conditions. If all the space in the
can was full of liquid, there would be the possible danger of the can bursting.

LIQUEFIED PROPELLANTS
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 head space as a vapour. As the product is used up as the valve is opened,
some of the liquid propellant turns to vapour and keeps the head space full of
vapour. 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 the formulation.

LIQUIFIED GAS
FLUORINATED HYDROCARBONS
Almost all types pharmaceuticals, Inhalation and oral use
Advantages
– Chemical inertness
– Lack of toxicity
– Non flammability & explosiveness
Disadvantages
– High cost
– It depletes the ozone layer
– Damage Global Warming Potential

HYDROCARBONS
– Can be used for water based aerosols, topical use
Advantages
– Inexpensive
– Stability & Purity
– Odorless!!
– Wide range of Boiling Points
– Wide range of Vapor Pressure
– Low Toxicity
– Excellent solvents
– It does not cause ozone depletion
Disadvantages
– Flammable
– Unknown toxicity produced
e.g. propane , butane , isobutane

Recently HFA propellants are used instead of CFC
propellants.

COMPRESSED GAS
PROPELLANTS
 Compressed gas propellants really only occupy the head space 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.
Unlike liquefied propellants, there is NO liquid to instantly vaporise when the
product emerges from the actuator, and only the product is sprayed out.

COMPRESSED GASES
 Used when the aqueous phase need not be miscible with the propellant.
 Do not have chilling effect, for topical preparation .
Advantages
– Inexpensive
– Non flammable
– No environmental problems
Disadvantages
– Pressure falls during use
– Produce coarse droplet spray
– Require use of non volatile co solvent
e.g. CO2, N2O, N2

Liquefied Petroleum Gas (LPG)
 Aerosol propellant grade LPG consists of high purity hydrocarbons derived directly
from oil wells, and as a by-product from the petroleum industry.
 They consist of a mixture of propane, isobutane and n-butane. These propellants
are used in most aerosols today, and have been used for many years in household
aerosol products.
 These gases are flammable, and this is reflected in the classification of aerosols
which contain them.
Di Methyl Ether (DME)
 This is an alternative liquefied propellant, and is more common in personal care
products, and some air fresheners
TYPICAL PROPELLANTS

Chlorofluorocarbons (CFCs)
These liquefied propellant gases used to be very common prior to the discovery that they
were affecting the ozone layer. They are no longer used in consumer aerosols in the western
world. They are however permitted in inhalation aerosols, as used in the treatment of asthma.
Non-soluble compressed Gasses. (e.g. Compressed Air and Nitrogen)
These are sometimes seen in consumer products, and are an environmental alternative to
LPG.
Soluble compressed Gasses (e.g. Carbon Dioxide)
This is another alternative to LPG, but has limited use, mainly with alcoholic systems,
such as air treatment products, deodorants and personal care products.

GENERAL
REQUIREMENTS
1. Propellants used in aerosol products shall meet the relevant Standards of BIS
(Bureau of Indian Standards) pertaining to safety, quality and performance.
2. The manufacture must produce the consent clearance as per the provisions of
water (Prevention and Control of Pollution) act 1981 along with the
authorisation, if required under environment (Protection) Act 1986 and the
rules made thereunder to BIS while applying for Ecomark.
3. The product package shall be suitably marked that the Ecomark label is
applicable only to the propellants used in aerosol sprays, if the product package
is not separately covered under the Ecomark Scheme.

4. Product package or leaflet accompanying it may display instructions of
proper use, storage and disposal so as to maximize the product
performance, safety and minimize wastage.
5. The material used for product packaging shall be made from recyclable or
biodegradable material.

BASIC
PROPELLANT
PROPERTIES

BASIC PROPELLANT
PROPERTIES
• Pressurize the aerosol package
• Influence the form in which the product is discharged:
 Foam
 Stream
 Spray

BASIC PROPELLANT PROPERTIES
Propellants also can act as:
• Solvent
• Diluent
• Viscosity modifier
• Freezant
• Refrigerant Refill Liquid

Chemical Name Numerical Vapour Pressure(psia) BP liquid Density(g/ml)
Designation 700
1300
F 0
F 0
C 700
F
Trichloromonofluorometha
ne
11 13.4 39.0 74.7 23.7 1.49
Dichlorodifluoromethane 12 84.9 196.0 -21.6 -29.8 1.33
Dichlorotetrafluroethane 114 27.6 63.5 38.4 3.6 1.47
Difluoroethane 152a 76.4 191.0 -11.2 -24.0 0.91
Butane A-17 31.6 82.0 31.1 -0.6 0.58
Isobutane A-31 45.8 111.0 10.9 -11.8 0.56
Propane A-108 122.8 270.7 -43.7 -44.6 0.50
PROPERTIES OF FLUOROCARBON AND HYDROCARBON
PROPELLANTS PHYSICOCHEMICAL
PHYSICOCHEMICAL PROPERTIES OF FLUOROCARBON AND
HYDROCARBON PROPELLANTS

Propellant Blend* Composition Vapour Pressure(psig) 700
F Density (g/ml) 700
F
12/11 50:50 37.4 1.412
12/11 60:40 44.1 1.396
12/114 70:30 56.1 1.368
12/114 40:60 39.8 1.412
12/114 45:55 42.8 1.405
12/114 55:45 48.4 1.390
Blends of Fluorocarbon Propellants for Pharmaceutical
Aerosols

PROPELLANT EXAMPLES
CHLOROFLUOROCARBONS:-
 propellant 12 (dichlorodifluoromethane), propellant 21 (dichlorofluoromethane),
 propellant 114 (1,2-dichloro-1,1,2,2-tetrafluoroethane),
 propellant 114a (1,1-dichloro-1,1,2,2-tetrafluoroethane),
 propellant 142b (1-chloro-1,1-difluoroethane),
 propellant 152a (1,1,-difluoroethane)

HYDRO CARBON PROPELLANTS:-
•Propane
•Isobutane
•Butane,
FLUOROCARBONS:-
• Octafluoropropane
• Octafluorocyclobutane
• Dimethyl ether
NON-CFC PROPELLANTS:-
Hydrofluoroalkanes:-
• Propellant 134a (1,1,1,2-tetrafluoroethane)
• Propellant 227 (1,1,1,2,3,3,3-heptafluoropropane).

THE MOLECULAR STRUCTURE OF PROPELLANT TO BE DERIVED
FROM THE NUMERICAL DESCRIPTOR THE RULES MAY BE LISTED
AS FOLLOWS:
1. The digit on the extreme right e.g.: propellant 114 (1,2-dichloro-1,1,2,2-
tetrafluoroethane) represents the number of chlorine atoms
2. The second digit from the right e.g.: propellant 114 (1,2-dichloro-1,1,2,2-
tetrafluoroethane) represent one more than the number of hydrogen atoms
3. The third digit from the right propellant 114 (1,2-dichloro-1,1,2,2-
tetrafluoroethane) represents one less than the number of carbon atoms.
4. The subscripted lowercase letter represent the symmetry of the molecule the earlier
in the alphabet the more symmetrical the molecule being described e.g.; propellant
114a (1,1-dichloro-1,1,2,2-tetrafluoroethane)Two additional rules have not been
required for pharmaceutical purposes but may be included for completeness
5. A forth number from the right indicates the number of double bonds in the
molecules.
6. A prefixed lowercase ‘c’ indicates that the molecule is cyclic

Vapor pressure of mixture of propellants is calculated by Dalton’s law which states
that total Pressure in any system is equal to the sum of individual or partial pressure of
various compounds .
Raoult’s law, which regards lowering of the vapor pressure of a liquid by the
addition of another substance, states that the depression of the vapor pressure of solvent
upon the addition of solute is proportion to the mole fraction of solute molecules in the
solution.

The relationship can be shown
mathematically
To calculate the partial pressure of propellant A:
Pa=(na/na + nb)pA0
=NApA
0
Where: Pa = partial vapor pressure of propellant A,
pA
o
= vapor pressure of pure propellant A
na = mole of propellant A,
nb = mole of propellant B
NA = mole fraction of component
A
To calculate the partial pressure of propellant B:
Pb =(nb/nb + na)pB
0
=NBpB
0
The total vapor pressure of system is then obtained as :
P = pa + pb
Where P = total vapor pressure of system

NONOZONE DEPLETING PROPELLANTS
The search for possible replacements for CFC for MID were defined in terms of
toxicity, flammability, chemical, physical properties and environmental
compatibility. The template for these properties, with the exception of
environmental suitability, were the existing MDI propellants, CFC 11, 12 and 114,
which had been safely and effectively for many years. The candidates that emerged
were hydrofluoroalkanes (HFA) specifically, tetrafluoroethane (HFA 134a) and
heptafluoropane (HFA 227) were recognized and potentially suitable MDI
propellants. These were non-flammable, non-ozone depleting, and chemical stable
propellants with suitable vapor pressures for MDI use.
Hydrofluoroalkanes contribute to the greenhouse effect but to a lesser extent than
CFC indicated in the table. It has been estimated that HFA from MDIs will
contribute less than 0.1% of total worldwide green house gas emission by 2005.
(INTERNATIONAL PHARMACEUTICAL AEROSOL CONSORTIUM).

ENVIRONMENTAL IMPACT OF MDI
PROPELLANTS
PROPELLANTS OZONE
DEPLETION
POTENTIAL
ATMOSPHERE
LIFE (YEARS)
GLOBAL
WARNING
POTENTIAL
CFC 11 1 60 1
CFC 12 1 125 3
CFC 114 0.7 200 3.9
HFA 134a 0 16 0.3
HFA 227 0 33 0.7

ADVANCES IN METERED DOSE INHALER TECHNOLOGY WITH THE
DEVELOPMENT OF A CHLOROFLUOROCARBON-FREE DRUG
DELIVERY SYSTEM
More than 440 million MDIs are produced every year, and that number is
estimated to grow to 800 million by the year 2000. MDIs have traditionally
contained chlorofluorocarbons (CFCs) as propellants. Although safe for human
use, scientific evidence shows that chlorine atoms in CFCs deplete the earth's
stratospheric ozone layer, which filters out the sun's harmful ultraviolet
rays. Over 144 signatory countries are now complying with the protocol in
banning the production of CFCs. Production of most CFCs in developed
countries ceased in January 1996. Intensive research led to the identification of
suitable alternative propellants and, ultimately, to the selection and development
of hydrofluoroalkane (HFA) 134a as the first nonozone- depleting MDI
propellant.

ADVANCES IN MDIs TECHNOLOGY
WITH CFC-FREE SYSTEMS
The standard first-line therapy for acute relief of asthma
symptoms is the use of beta-agonists, and the most widely used
compound in this class is Salbutamol (Albuterol). For this
reason, Salbutamol was the first bronchodilator considered for
reformulation in a new CFC-free system. 3M Pharmaceuticals
developed the first CFC-free MDI containing Salbutamol
sulfate in an HFA- 134a propellant system.

ADVANTAGES
1. Consistent dosing through the end of canister life
2. Consistent dosing at all storage orientations
3. Reliable dose delivery at low temperatures(This can be of
concern to patients who live or work in environments where
the temperature is considerably lower than room temperature
or to those who use their inhalers for cold-induced asthma
symptoms.)

CFC DISADVANTAGE
1. CFC products also tend to produce a cold blast
striking the back of a patient's throat, resulting in
patient discomfort and poorer drug delivery.
2. Dosing could be inconsistent toward the end of
the life of the container and was sensitive to
temperature extremes, storage time.

INTEGRATING CHEMISTRY AND
PROCESS
This research program seeks to tackle HFC reformulation
challenges from two aspects:
1. Characterizing the surface interaction between the
formulation components, and
2. Introducing process benefits by integrating chemistry
with new milling techniques to improve HFC dispersions of
MDI medicaments.

ULTIMATE GOALS
The ultimate goals are:
To use a fundamental understanding, rather than a trial-and-
error, reformulation approach
Integrate formulation and process development, and
Accomplish HFC performance equivalent to CFC performance
in MDIs Research has proceeded in two phases.
The first phase evaluates
Chemistry of formulation components with various asthma
medicaments.
The second phase
Advances optimized formulations to processing in a high-
pressure media mill.

FORMULATION CHEMISTRY
Experiments were conducted to understand interactions of the
basic MDI formulation
 Drug active
 Surfactant
 Co-solvent
 Propellant
In doing so, each formulation component was characterized by
certain physical properties judged to be important to the surface
interactions.

The MDI medicaments were characterized by:
log POW (Octanol-water partition coefficient)
Density
Particle size
Surface energy
Morphology
The propellants were characterized by:
Density
Dielectric constant
The surfactants were characterized by:
Head/tail structure
Molecular weight
Chemistry

PHYSICAL PROPERTIES FOR THE
PROPELLANTS
HFC 134a HFC 227ea
Boiling Point °C -26.1 -15.6
Vapor Pressure
@ 25°C
Bar 6.7 4.5
Liquid Density @
25°C
g/cc 1.2 1.4
Dielectric
Constant
- 9.5 4.1
Dipole Moment D 2.1 0.9
This high-pressure media milling (HPMM) process yields stable, fine particle
dispersion of medicament in liquid HFC propellant. The milling is performed
with the entire MDI formulation so that surfactants and cosolvents are
available to the drug actives during the milling process. Milling is believed to
increase dispersion stability because having the surfactant available during
milling results in improved deposition or adsorption onto the surface of the
medicament particles as they are milled.

A second advantage for HPMM process using HFC
propellant as the medium is that, when milling is complete, it
is the final formulation that is available. Conceptually, the
batch in the mill can be filtered and directly packaged to the
MDI container, offering a potential improvement in
commercial processing productivity, cost and quality.
The HPMM process produces medicament dispersions in
liquefied HFC propellant that are stable for long periods of
time and that are easily re-suspended if they do settle.

IDEAL PROPERTIES
The ideal propellant for use in an MDI will exhibit the
following properties:
Non-toxic
Inert and unreactive in the formulation
Chemically stable under a range of conditions
High purity
Acceptable taste and odor

CONCLUSION
 HFAs provide a safe alternative to CFCs as propellants in these
devices but their physicochemical properties have required
extensive redevelopment of the entire product.
 HFAs are not environmentally neutral and contribute to
hydrocarbon emissions, global warming and acid rain. Nevertheless,
the contribution of HFAs to environmental damage is considered to
be comparatively small and the health benefit of drugs formulated
using HFAs currently outweighs the environmental concerns, but
this may not continue indefinitely.
 The technical challenge to reformulate MDIs has almost been
achieved and the next challenge is the transition of patients from
CFC-MDIs to the new products.

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 1000-1017

INTERNET LINKS
http://en.wikipedia.org/wiki/Aerosol_spray
http://www.yorks.karoo.net/aerosol/link4.htm
http://www2.dupont.com/Medical_Device_Materia
/en_US/assets/downloads/metered_dose.pdf
http://ww.aboutaerosols.com/industry.php
http://www2.dupont.com/Medical_Device_Material
/en_US/assets/downloads/metered_dose.pdf
http://www.liebertonline.com/doi/abs/10.1089/j
m.1999.12.151
http://en.cnki.com.cn/Article_en/CJFDTOTAL
GWYZ200803012.htm
http://www.docstoc.com/docs/13418747/ECOMARK-CRITERIA-FOR-
AEROSOL-PROPELLANTS

Thank you
for
sharing this time!

Propellents

More Related Content

What's hot

Viewers also liked

Similar to Propellents

More from Sunil Boreddy Rx

Recently uploaded

Propellents