Acid-catalyzed degradation of clarithromycin and erythromycin B: a comparative study using NMR spectroscopy.

One of the major drawbacks in the use of the antibiotic erythromycin A is its extreme acid sensitivity, leading to degradation in the stomach following oral administration. The modern derivative clarithromycin degrades by a different mechanism and much more slowly. We have studied the pathway and kinetics of the acid-catalyzed degradation of clarithromycin and of erythromycin B, a biosynthetic precursor of erythromycin A which also has good antibacterial activity, using (1)H NMR spectroscopy. Both drugs degrade by loss of the cladinose sugar ring and with similar rates of reaction. These results suggest that erythromycin B has potential as an independent therapeutic entity, with superior acid stability compared with erythromycin A and with the advantage over clarithromycin of being a natural product.