Pharmaceuticals photochemical reactions

CECILIA M. PERALTA; LILIANA P. FERNÁNDEZ

Radiation Exposure: Sources, Impacts and Reduction Strategies

Nova Sciences Publishers

Año: 2011; p. 167 - 188

Photolytic degradation can be a major limiting factor in the stability of pharmaceuticals. A drug may be chemically affected by the radiation of a particular wavelength only if it absorbs radiation at that wavelength and if the power exceeds a threshold. Ultraviolet radiation, which has a high energetic level, is the cause of many degradation reactions. If the molecule absorbs radiation, it produces excited states of itself and may react photochemically with other specie. When absorbing molecules are not directly involved in the reaction, but they transfer their energy to other reactive molecules, the absorbing substance is called photosensitizer. Due that many experimental variables may be involved in photochemical reaction, the kinetic may be very complex. The intensity and wavelength of light and the size, shape, composition and color of the container can affect the reaction rate. Photodegradation of some pharmaceuticals follows zero order kinetics; moreover others are degraded following a kinetic of first order. This chapter includes: a) The use of UV radiation for degradation of pharmaceuticals present in industrial waste. b) The use of UV radiation to catalyze the reaction of omeprazole degradation, and their determination based on the modification in the fluorescent properties.