STABILITY OF ERYTHROMYCIN AND SOME OF ITS ESTERS IN METHANOL AND ACETONITRILE

The stability of erythromycin (EB), erythromycin ethylsuccinate (EES), propionyl erythromycin (PE) and erythromycin estolate (EE) in methano l and acetonitrile was investigated. Methanol is widely used asa solve nt for EB and its ester derivatives in compendial identification tests as well as in the sample preparation steps during assay procedures. H PLC with electrochemical detection was used to measure EB concentratio ns in methanol and acetonitrile solutions - incubated at room temperat ure (20 +/- 0.5 degrees C) over various periods of time. EB was relati vely stable in methanol or acetonitrile, remaining intact for over 168 h in acetonitrile and showing less than 5% degradation in methanol ov er the same period. Approx. 87% of PE remained intact after 168 h in a cetonitrile whilst methanol caused rapid hydrolysis to EB (35% remaini ng after 28 h). Similarly, EES was unstable in methanol, showing rapid and almost complete hydrolysis to EB, with less than 5% remaining aft er 40 h. Less than 5% degradation, however, occurred over a period of 168 h when EES was dissolved in acetonitrile. EE appeared to be unstab le in both acetonitrile and methanol. In acetonitrile, only 13% of EE remained intact after 168 h, whereas in methanol, the degradation was much more rapid with 35% of EE remaining after 28 h.