Courses:Components of aerosol
From Pharmpedia
3.What are the different components of Aerosol product? Explain the characteristics of each component.
The aerosol product essentially is a combination of gases used for dispersion of the drug/drugs packaged under high pressure in a container. Valve assembly is an important component which helps in easy opening and closing of the container and delivering the product in the desired form. The valve is connected to the actuator. Actuator is a button, which when pressed releases the product into the atmosphere.
The schematic representation of the aerosol product on closed and open position is shown in figure 3. Thus the aerosol product consists of the following components:
1.Propellant
2. Container
3. Valve and Actuator and
4. Product concentrate
Propellants: The propellant is generally regarded as the heart of the aerosol package. It is responsible for development of pressure within the container, supplying the necessary force to expel the product when the valve is opened. The propellant also acts as a solvent and as a diluent and has much to do with determing the characteristics of the product as it leaves the container.
Various chemical compounds have been used as propellants in MDIs and include:
1.Chloro fluoro carbons(CFC) 2.Hydro fluoro alkanes (HFA)
1. Fluorinated hydrocarbons
Fluorinated hydrocarbons also called fluorchlorocarbons, chlorofluorocarbons (CFC’s) are inert, non toxic, non-inflammable used for oral and inhalation aerosols. Among the fluorinated hydrocarbons trichlorofluoromethane (Propellant 11), dichlorodifluoromethane (Propellant 12) and dichlorotetrafluoroethane (Propellant 114) were initially widely used in pharmaceutical aerosols. However, the depletion of ozone layer caused by CFC’s has restricted their use to oral and inhalation products such as antibiotics and steroids to name a few. This has led to the use of other propellants for topical use.
Si.no Propellant Composition Vapor pressure (psig 70ºF)
1. Trichloro mono fluoro methane Propellant 11 11 / 12 in 50 :50 37.4
2. Dichloro di fluoro methane Propellant 12 11/12 in 60:40 44.1
CFC’s depending on their chemical structures have varying vapor pressures and density. Depending on the vapor pressure and concentration of the propellant, the product is obtained in different physical forms such as sprays, mist, solid stream or foam. Usually, the combination of propellants has to be used to obtain the desired vapor pressure. The vapor pressure of the mixture of propellants is calculated according to Dalton’s law, which states that the total pressure in any system is equal to the sum of the individual or partial pressure of various components. Various blends of fluorinated HC are used in order to get the desired vapor pressure.
In order to overcome the effect of chlorofluorocarbons on the ozone layer, the hydro fluoro alkanes are being used as propellant such as HFA 21 in pulmonary systems.
Containers Different materials are used for the manufacture of aerosol containers. The materials must be inert, non-toxic and must withstand pressure as high as 140 to 180 psig at 130ºF.
1. Metal A. Tin-plated steel a.Side – seam (three piece) b.Two – piece or drawn B.Aluminum a.Two-piece b.One-piece (extruded or
drawn) C.Stainless steel
2.Glass A.Uncoated glass B.Plastic – coated glass
Let us look into the characteristics of each of these containers
Tin-Plated Containers:
The tin-plated steel containers consist of a sheet of steel plate which has been coated on both sides with tin. The thickness of the tin coating is described in terms of its weight such as #25, #50 and #100. The size of the container is indicated by a standard system, which is a measure of the diameter and height of the container. A container said to be 202 x 214 is 2 x 2/16 inches in diameter and 2 x 14/16 inches in height.
Tin-plated steel is obtained in thin sheets and when required coated with an organic material. The sheet is cut into pieces to make a body, a top and a bottom. The body is shaped into a cylinder and soldered. The top and bottom are attached to the body and a side seam stripe is added to the side seam area.
Aluminum Containers: Aluminum is used to manufacture extruded or seamless aerosol containers. Many of the pharmaceuticals are packaged in aluminum containers because of the lessened danger of in-compatibility due to its seamless nature and greater resistance to corrosion. However, aluminum can be corroded by pure water and pure ethanol. The combination of ethanol and propellant II in an aluminum container has been shown to produce hydrogen, acetyl chloride, aluminum chloride, propellant 21 and corrosive products.
Stainless steel Containers: Stainless steel containers are limited to small size because of production problems and cost. They are extremely strong and resistant to most materials. No internal organic coating is necessary.
Glass Containers Glass containers have been used for a large number of aerosol pharmaceuticals available with or without plastic coatings. Advantages are elimination of compatibility problems, degree of flexibility in design. The organic coatings provide added protection to the glass container.
Valves Valve must be multifunctional in that it is capable of being easily opened and easily closed and capable of delivering the contents in the desired form. Also in case of metered dose inhaler aerosol, the valve is expected to deliver a given amount of medication. Thus there are mainly two types of valves:
1.Continuous spray valves mainly used in topical products and non pharmaceutical products 2.Metering valves used in MDIs
We shall look into the details of the design and components of continuous spray valve which was modified to form the metered dose inhalers
Continuous Spray valve
Consists of different parts which are assembled together using high speed production technique. Typical aerosol valve assembly is shown in figure 6 and consists of
1.Ferrule or Mounting cup 2.Valve body or Housing 3.Stem 4.Gasket 5.Spring 6.Dip tube
Ferrule or Mounting cup
The ferrule or mounting cup is used to attach the value proper to the container. It is generally made from tin-plate steel or aluminum depending on the dimension of the opening of the container. The underside of the valve cup is exposed to the contents of the container and to the effects of oxygen trapped in the head space. To increase the resistance to corrosion a single or double epoxy or vinyl coating is added to the underside of the mounting cup. Ferrules that are used with small aluminum tubes or with glass bottles are made from softer metal such as aluminum or brass.
Valve Body or Housing
The valve body or housing is generally manufactured from nylon or Delrin. The housing has the dip tube attached at its bottom.
Stem
Stem is made from nylon or Delrin, but metals such as stainless steel can be utilized. One or more orifice is set into the stem; they range from one orifice at about 0.013 inch to 0.030 inch, to three orifices of 0.040 inch each.
Gasket
Gasket is made from Buna-N and Neoprene rubber as they are compatible with most pharmaceutical formulations.
Spring Spring serves to hold the gasket in place and is made of stainless steel. When the actuator is depressed and released, it returns the valve to its closed position
Dip tube
Dip tube is made of polyethylene or polypropylene, the inside diameter varies from 0.120 inch to 0.125 inch.
Metered dose inhalation are designed to deliver the dose of medication into the nasal and respiratory airways. This reduces the number of administration errors in pharmaceutical aerosols.
Actuators
The actuator is a specially designed button which delivers the product in a proper and a desired form. It is fitted to the valve stem. It allows easy opening and closing of the valve and is an integral part of every aerosol package. It serves to aid in producing the required type of product discharge. There are many types of actuators. They produce different forms of final product and include 1. Spray actuator 2. Foam actuator. 3. Solid stream. 4. Special applications.
Spray Actuators Are capable of dispersing the stream of product concentrate and propellant into relatively small particles
by allowing the stream to pass through various openings (of which there may be one to three on the order of 0.016 inch to 0.040
inch in diameter). If the percentage of propellant 12 is more, larger openings can be used. Thus combination of propellant
vaporization, orifices in the actuator and the internal channels can deliver the spray in the desired particle size. Uses 1.Oral
and Inhalation products 2.Topical use Spray on bandages Local anesthetics Antiseptics Food
preparations
When the concentration of propellant is less the product is dispensed as a stream since the propellant is not sufficient to dispense the product fully. Such cases mechanical breaking a stream into fine particles by causing the stream to swirl through various channels will help in obtaining a fine dispersion.
Foam Actuators Consist of large orifices ranging from 0.070 to 0.128 inches. The product is dispensed into a relatively large chamber where it can expand and is then dispersed through the large orifices. The product contains a small concentration of propellant of low vapor pressure which further aids in foam production.
Solid Stream These actuators are mainly used for ointments. They are similar to foam type. The product expands and dispersed through a large orifice. Special Actuators are designed to deliver the medication to the appropriate site of action – throat, eye, and nose.
FIG 8
Metering valves
Metering valves are modification of the continuous spray valve that has been explained above in detail. It is designed to deliver specific quantity of a product each time the They operate on the principle of a chamber size whose size determines the amount of medicament to be delivered.
A dose of 50-150mg 10%of liquid material can be dispensed using metering valves. le to the dispensing of potent medicament.
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