Quantitative assessment of photostability and photostabilisation of Fluvoxamine and its design for actinometry.

Despite the numerous concerns that have been raised in relation to considering 0th, 1st and 2nd–order kinetic treatments for drugs’ photodegradation characterisation and assessments, yet they still are employed, as the only tool available for these types of studies. The recently developed –order kinetic models have opened new perspectives in the treatment of photoreaction kinetics that stands as the best known alternative to the classical approach. The –order kinetics have been applied here to Fluvoxamine (Fluvo) with the aim to set out a detailed and comprehensive procedure able to rationalise photodegradation/photostability of drugs and propose a platform for photosafety studies. Our results prove that drugs’ quantum yields (0.0016 <Φ􀮿􀯟􀯨􀯩􀯢 􀰒􀳔􀳝􀳝 < 0.43) should a priori be considered wavelength–dependent, their photostabilisation (up to 75% for Fluvo) by means of absorption competitors could explicitly be related to a decrease of the photokinetic factor, and photoreversible drugs can be developed into efficient actinometers (as Fluvoxamine in the 260–290 nm range). A pseudo– rate–constant factor was proposed as a descriptive parameter, circumventing the limitations of overall rateconstants and allowing comparison between drugs’ kinetic data obtained in different conditions.