Other Properties of Excipients

4-Benzodiazepines undergo hydrolysis of the azomethine and amide groups by acid catalysis. Anionic surfactants such as sodium dodecyl sulfate inhibited hydrolysis of the 

The effect of surfactants on the degradation of pi-lactam antibiotics is difficult to interpret. As shown in Fig. 116, acid degradation of propicillin in solutions was inhibited by polyoxyethylene-23-laurylether (a nonionic surfactant) and CTAB (a cationic surfactant) but enhanced by sodium lauryl sulfate (an anionic surfactant).485 Degradation of cefaclor (an a-aminophenyl cepalosporin) was enhanced by CTAB. The dependence on salt concentration suggests a complex mechanism for the effect of surfactants on degradation of cefaclor.486 

Excipients such as cyclodextrins, which form inclusion complexes with drug substances, can have a significant effect on drug stability. These effects will be described in 

Detailed mechanisms are not clear in other reports of the effects of excipients on drug stability. For example, bropirimine was destabilized by solubilizers (such as polyethylene glycol),495 whereas water adsorbed on porous montmorillonite exhibited a catalyzing effect on the degradation of aspirin.496 Some excipients appear to have minimal effects on drug stability for example, fluocinolone acetonide in a cream formulation exhibited the same degradation as in aqueous solution without the excipients present in the cream formulation.497 

Another factor affecting drug stability is electrical current. The stability of hydrocortisone hemisuccinate and phosphate esters as their sodium salts was affected by a change in pH that occurred when current was applied during an iontophoresis study.506 Degradation of propranolol hydrochloride in an electrically modulated drug delivery device has been reported.507 

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