ICH guideline for photostability testing: aspects and directions for use.

The ICH guideline Q1B for photostability testing gives guidance on the basic testing protocol required to evaluate the light sensitivity and stability of new drugs and products. The choice of the irradiation method, although complying with the guideline demands, may effect test results. High irradiances may shorten testing times, but can lead to enforcement of photodegradation, which was demonstrated for molsidomine tablets. The exposure to an artificial light source (xenon lamp) was compared and correlated to natural daylight. Suitable testing methods for nifedipine and molsidomine tablets were developed. Deviating from the guideline recommendations, the presentation of powder samples should be done in tiny aluminium pans, facilitating the test procedure, minimising the risk of falsified test results due to improper sampling and improving reproducibility. When using glass dishes for the presentation of tablets to photostability testing, they should be lined by e. g. aluminium foil to avoid influences of light reflected from the sample tray.