Some erythromycin derivatives are strong inducers in rats of a cytochrome P-450 very similar to that induced by 16 alpha-pregnenolone carbonitrile.

Erythromycin derivatives having lost the cladinose moiety, erythralosamine and its mono- and diacetate, are strong inducers of liver cytochrome P-450, better than troleandomycin, in rats. The major cytochrome P-450 form induced by all these macrolides is electrophoretically and immunologically indistinguishable from the major form induced in rats by pregnenolone carbonitrile. This form is particularly able to metabolize the macrolides and to lead to the corresponding 456 nm absorbing cytochrome P-450 metabolite complexes in vivo and in vitro.