Lack of effect of amoxicillin on theophylline pharmacokinetics

The effect of the antibiotic drug amoxicillin on steady state pharmacokinetics of theophylline was studied in healthy adults by comparing the pharmacokinetic parameters as found during a 9 day course of theophylline alone and as obtained during comedication with amoxicillin. Theophylline plasma concentrations were measured by means of h.p.l.c. analysis. On the ninth day of each of the two periods of drug administration a concentration-time curve was evaluated. It showed no influence of amoxicillin on absorption, elimination and volume of distribution of theophylline, as a result of which mean steady state plasma concentrations were not significantly different during both treatments. It is concluded that both drugs can be given concomitantly without any dosage adjustment of theophylline.