Gastrointestinal Behavior of Orally Administered Radiolabeled Erythromycin Pellets in Man as Determined by Gamma Scintigraphy

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Abstract
The behavior of single 250‐mg doses of a multiparticulate form of erythromycin base (ERYC(R)), each including five pellets radiolabeled with neutron‐activated samarium‐153, was observed by gamma scintigraphy in seven male subjects under fasting and nonfasting conditions. The residence time and locus of radiolabeled pellets within regions of the gastrointestinal tract were determined and were correlated with plasma concentrations of erythromycin at coincident time points. Administration of food 30 minutes postdosing reduced fasting plasma erythromycin Cmax and area under the plasma erythromycin versus time curve (AUC) values by 43% and 54%, respectively. Mean peak plasma concentration of erythromycin (Cmax) in the fasting state was 1.64 μg/mL versus 0.94 μg/mL in the nonfasting state. Total oral bioavailability, as determined by mean AUC (0‐∞) of the plasma erythromycin concentration versus time curve, was 7.6 hr/μg/mL in the fasted state, versus 3.5 hr/μg/mL in the nonfasting state. Mean time to peak plasma erythromycin concentration (tmax) in the fasting state was 3.3 hours, versus 2.3 hours in the nonfasting state. Plasma concentrations of erythromycin in both fasting and nonfasting states were within acceptable therapeutic ranges. Evidence provided by this study: 1) indicates that pellet erosion and absorption of active erythromycin base begins when the enteric‐coated pellets reach the highly vascular mucosa of the jejunum and proximal ileum, and is essentially completed within the ileum, with a significant portion absorbed in the medial‐to‐distal ileum; 2) confirms that acceptable therapeutic plasma levels of erythromycin are attained in nonfasting subjects (Cmax = 0.94 μg/mL) and that superior plasma erythromycin concentrations (Cmax = 1.64 μg/mL) are achieved by administration of the dose on an empty stomach 1 to 2 hours before or after meals; 3) corroborates other comparative studies reporting greater fasting bioavailability with this multiparticulate dosage form of erythromycin base than with reference single tablet or particle‐in‐tablet formulations; and 4) indicates that neutron activation of stable isotopes incorporated as a normal excipient in industrially‐produced formulations provides an effective means for in vivo evaluation of dosage forms through gamma scintigraphy.