title: The interaction of erythromycin with theophylline.
abstract: We have studied the interaction of erythromycin with theophylline. We gave ten healthy volunteers theophylline as an intravenous loading dose (5 mg X kg-1) over 1 h, followed by a maintenance infusion (0.5 mg X kg-1 X h-1) for 5 h. A second infusion of theophylline was given after 9 days of treatment with 1 g erythromycin base daily, and the concentrations of theophylline were determined during the infusion periods. The concentrations of erythromycin were measured for 8 h, after one week of treatment, and also after the last erythromycin dose, simultaneously with the second theophylline infusion. Concentrations within the therapeutic range were obtained with both drugs. A significant increase in both AUC and mean plasma concentrations of theophylline was seen during erythromycin treatment. The plasma clearance of theophylline was reduced in 9 of the 10 subjects. Renal clearance increased correspondingly, but the change was not statistically significant. Serum concentrations of erythromycin fell significantly, by more than 30%, with concurrent theophylline medication. We conclude that an interaction between theophylline and erythromycin, affecting both drugs, can be shown with concentrations of the drugs within the therapeutic range.
mesh_terms: D000328:Adult; D004347:Drug Interactions; D004917:Erythromycin / Q000008:administration & dosage* / Q000097:blood; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D013806:Theophylline / Q000008:administration & dosage* / Q000097:blood
chemical_list: D004917:Erythromycin; D013806:Theophylline