Page 73 - Quality control of pharmaceuticals (07-PA 704)

The photostability of a drug substance may be defined as the response of the drug or
drug product to the exposure to solar, UV, and visible light in the solid, semisolid,
or liquid state that leads to a physical or chemical changes.
The response of the drug to light absorption and excitation can be considered in
terms of photodegradation (photolysis) reactions through the formation of free
radicals or photosensitization reactions by intermolecular energy transfer. These
reactions involve primary (photochemical) and secondary (chemical) reactions that
give the final products.
Examples:
Ketoprofen (KP) undergo photodecarboxylation reaction upon exposure to
UV/Visible light and forms a highly reactive carbanion intermediate which further
undergo protonation to produce 3-ethylbenzophenone, a photoallergic component
resulting in erythema, edema, and pigmentation adverse effects with KP transdermal
formulations. Thus, ketoprofen (KP) gels were withdrawn from markets in Spain
and France in late 2009 due to numerous photosenitivily reactions. The European
Medicines Agency conducted a review of the safety and efficacy data of ketoprofen,
and, based on the assessment of risk-to-benefit ratio, the marketing authorization
was changed from over- the- counter to prescription drug.
In a solid state, Ranitidine produces an unpleasant sulphur-like odor and thus it
could be suspected that some volatile, odorous chemicals are produced from RAN
during its degradation in a solid state, but no published reports concerning this issue
were found.
Other volaties produced during photodegradation may show genotoxic and
mutagenic effects stronger than the respective parent compound.
Drugs that contain two phenolic groups, such as adrenaline (epinephrine) and other
catecholamines such as noradrenaline (norepinephrine) and isoprenaline are