Bioavailability and effect of food on the gastrointestinal absorption of two erythromycin derivatives

The concentrations of erythromycin in the serum were comparable after a single 500 mg oral dose of two brands of erythromycin stearate (Resibion and Erythrocin) in six healthy fasting volunteers. There was no significant difference in their pharmacokinetics. Over a period of 24 hours, 4 and 5% of the 500 mg dose of each preparations was excreted in the urine. Analysis of serum erythromycin concentration data were performed according to a one-compartment open model. The short half-life in the serum (1.43-1.78 hours), small portion of the dose excreted in the urine (4-5%), and the low renal clearance value (0.43-0.51 ml/min/kg) indicate that the majority of erythromycin is extensively cleared by extrarenal mechanisms. In addition, serum concentrations of erythromycin were measured during continuous treatment (250 mg base every 6th hour) with erythromycin stearate (Resibion) or enteric-coated erythromycin base (Etromycin) in ten healthy volunteers, in both fasting and non-fasting conditions. Again in the fasting state the serum levels were comparable and those from both the stearate and base were markedly reduced by food.