Steady state urinary excretion of theophylline and its metabolites in the presence of erythromycin.

The effect of erythromycin on the quantitative pattern of urinary excretion of theophylline and its known metabolites at steady state in eight human subjects was examined. The percent of dose excreted of the various compounds in the absence and presence of the antibiotic were as follows: theophylline, 9.3% vs. 16.3%; 1, 3-dimethyluric acid, 51.9% vs. 59.6%; 3-methylxanthine, 11.9% vs. 13.0%; and 1-methyluric acid, 27.3% vs. 31.6%. These results show that erythromycin did not influence the metabolism of theophylline under the experimental protocol employed.