Courses:Pulmonary Drug Delivery/Stability testing of aerosol
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6.Stability testing of aerosol
Describe in detailhow the stability program is conducted on aerosol products?
A stability program for aerosol formulation consists of an examination of all materials used in the product both separately and collectively. Usually propellants do not present any problem because of their stability. The important characteristics of the product, especially in a metered dose inhaler is the compatibility of the active ingredients with the propellant, container and valve.
The parameters to be evaluated vary depending on the type of product to be evaluated and include:
1.Metered dose inhalers, oral and nasal aerosols: Pressure, weight loss, total medication, can content, weight uniformity, moisture content, valve delivery, particle size, unit spray, degraded product, content uniformity, particulate matter and interaction of product with can.
2.Topical Sprays Pressure, weight loss, delivery rate, specific gravity, density, viscosity, interaction of the product with
valve, interaction of product with containers, other depending upon on the nature of the product.
3.Foams Same as sprays, foam density and characteristics, amount delivered if metered, amount delivered if non-metered.
The effect of container on the product and the effect of product on the container and the value and dip tube must be studied. All
materials must be studied separately and collectively
The testing of aerosols thus include 1.Concentrate and Propellant 2.Container and 3.Valve
Concentrate and Propellant:
Immediately after preparation, several of the important physicochemical constants of the product are determined. They include: 1. Vapor pressure 2. Spray rate of valve 3. pH 4. Density or specific gravity 5. Refractive Index 6. Viscosity 7. Total weight 8. Assay of active ingredients 9. Infrared and or gas chromatography curves 10. Color and odor
These valuations are then used for comparison during the entire testing process. The samples are usually stored on their sides so that the product comes into contact with the value, mounting cup and container.
Container:
The contents of the container are removed by chilling the contents to a temperature of 0ºF or less and opening the container. The container is then examined for signs of corrosion. These changes can be detected without much difficulty in the form of small pinholes, softening of larger (If larger is present) or larger may be dissolved, peeled or blistered by the concentrate. Special attention should be paid to the side seam and headspace as there can be corrosion in these regions, incase of glass containers, examination of the container may not be necessary. In case of plastic container, special testing has to be done to determine whether leaching or sorption has taken place.
Valve: Should be examined to ensure that it is functional and easily dispense the product and can be easily closed. The valve cup should be examined for corrosion. The various valve subcomponents should be examined for evidence of softening, cracking, elongation or distortion. Also elongation and cracking of the dip tube should be checked.
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