Factors Affecting Photodegradation in Solutions

Many solution reactions are catalyzed by hydrogen or hydroxyl ions and consequently may undergo accelerated decomposition upon the addition of acids or bases. The catalysis of a reaction by hydrogen or hydroxyl ions is known as acid-base specific catalysis. In many cases, in addition to the effect of pH on reaction rate, there may be catalysis by one or more species of the buffer system. This type of catalysis is known as the acid-base general catalysis. Solutions of vitamin were found to be 

The photodegradation of doxorubicin, daunorubicin, and epirubicin is accelerated by increases in the pH of their solutions (61). Furosemide is stable in alkaline solutions, but quickly degraded in acid solutions (62). 

Drug molecules in solution are also catalyzed by the actual buffer species chosen and its molarity, in addition to the normal hydrogen and hydroxyl ions catalysis. The catalytic effect of various buffer species on the photodegradation rate of some drugs has been reported in the literature. 

Citrate and phosphate ions were found to catalyze the photodegradation of sulfacetamide and sulfanilamide (63). Adriamycin is most stable in a citrate buffer, followed by phosphate and then acetate buffer (47). The order of the catalytic effect of buffer species for metronidazole was found to be citrate acetate phosphate buffer (68). Acetate ions were found to be most detrimental to the photostability of 

The photolysis of demeclocycline hydrochloride, in the presence and absence of glutathione as a photoprotective agent, was lowest in citrate buffer when compared to acetate or phosphate buffers (76). Table 2 shows the magnitude of this effect. 

---