Bioavailability of erythromycin acistrate from hard gelatin capsules containing sodium bicarbonate.

Erythromycin acistrate is a new prodrug of erythromycin. Its bioavailability from hard gelatin capsules containing the drug with or without sodium bicarbonate was studied in healthy volunteers. The plasma levels of erythromycin, anhydroerythromycin, and acetylerythromycin were measured using an HPLC method. Addition of sodium bicarbonate to the capsule markedly enhanced the plasma level of the microbiologically active substance, erythromycin, doubling the Cmax and AUC values (P less than 0.05). At the same time, the lag time in the absorption curve was shortened to one-third. No changes in the plasma levels of the inactive metabolite anhydroerythromycin were noted. It is concluded that adding sodium bicarbonate to an erythromycin acistrate formulation enhances its bioavailability.