Bioinequivalence of erythromycin ethylsuccinate and enteric-coated erythromycin pellets following multiple oral doses.

Bioequivalence comparisons between erythromycin ethylsuccinate and an enteric-coated erythromycin base pellet product were made following multiple-dose, oral administration. Twenty-four volunteers participated in a ten-dose protocol (one dosage unit every six hours) using a complete crossover design. Plasma samples were assayed using a microbiological method specific for erythromycin base in the presence of the ester. Without correcting for the differences in doses administered, the amount of active erythromycin base absorbed from the enteric-coated pellet (250 mg base) was five to seven times that absorbed from the erythromycin ethylsuccinate product (400 mg base equivalent) at steady state. Erythromycin ethylsuccinate is not bioequivalent to an enteric-coated erythromycin base pellet product. The lower bioavailability of the ethylsuccinate may be due to instability in the acidic medium of the stomach.