Procedure for Photostability Exposure

PROCEDURE FOR PHOTOSTABILITY EXPOSURE Selection of a Suitable Photostability Testing Cabinet 

The photostability testing of drug substances should be performed using a wavelength band that is related to real conditions. A helpful guidance is the definition of the spectral power distribution for solar spectral irradiance defined by the 

Commission Internationale de TEclairage (CIE) (5) and discussed in Chapter 6 of this book. 

Daylight exposure as a natural photon source has its restrictions due to within day, daily, seasonal, and terrestrial variation. Artificial photon sources are more reproducible and therefore an indispensable prerequisite for standardized photostability testing. 

Many investigators employ xenon lamps because they have a continuous spectrum and cover the UV, VIS, and short infrared (IR) bands similar to solar irradiance. The use of an IR dichroic mirror in combination with a UV filter for fhe UV band with these lamps produces a very close simulation of the daylight irradiance (Fig. 1). 

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