Influence of gatifloxacin, a new quinolone antibacterial, on pharmacokinetics of theophylline.

The influence of gatifloxacin, a new quinolone antibacterial, on the pharmacokinetics of theophylline (TP) was studied in five healthy adult male volunteers. After 200 mg of TP in sustained-release preparation was administered twice daily for 4 consecutive days, the same dose of TP and 200 mg of gatifloxacin were administered concurrently to the subjects twice daily for 5 consecutive days. Comparison of the pharmacokinetic parameters on day 4 of TP alone, and days 3 and 5 of co-administration revealed no significant differences in the maximum concentrations (Cmax), areas under the serum concentration-time curve (AUC0-12), total body clearances, and the amounts and proportions of TP and its metabolites in urine. One subject, however, showed 55% and 44% increases in Cmax and AUC0-12, respectively, on day 5 of co-administration relative to values on day 4 of TP alone. Thus, co-administration of gatifloxacin seemed to have little effect on the pharmacokinetics of TP. Further studies will be necessary to clarify the pharmacokinetic interaction between quinolones and TP, and it is recommended that, when both gatifloxacin and TP are administered, the background of the patients, such as their age, liver and cardiac functions, and other concomitant medications, be considered.