EVALUATION OF THE INTESTINAL-ABSORPTION OF ERYTHROMYCIN IN MAN - ABSOLUTE BIOAVAILABILITY AND COMPARISON WITH ENTERIC-COATED ERYTHROMYCIN

To determine the role of acid hydrolysis on the gastrointestinal absor ption of erythromycin, six healthy subjects received erythromycin as a 240 mg Intravenous dose, a 250 mg oral solution administered via endo scope directly into the duodenum and bypassing the stomach, and an ent eric-coated 250 mg capsule. Blood samples were collected for 6 hours a nd serum erythromycin quantified by a microbiological method. The time to achieve maximum serum concentrations for the solution was 0.25 +/- 0.08 (mean +/- SD) hours and for the capsule was 2.92 +/- 0.55 hours. The absolute bioavailability of erythromycin from the capsule was 32 +/- 7% and for the duodenal solution 43 +/- 14%. The ratio of the area s under the serum erythromycin concentration-time curve of capsule to solution was 80 +/- 28% (range 38 to 110%). There is substantial loss of erythromycin apart from gastric acid hydrolysis, which cannot be ac counted for by hepatic first-pass metabolism. Attempts to further impr ove the oral bioavaitability of erythromycin beyond 50% by manipulatio n of formulation are likely to be futile.