OBJECTIVE To investigate the pharmacokinetic interaction between ciprofloxacin and itraconazole in healthy male volunteers. METHODS Ten healthy male volunteers were assigned into a 2-sequence, 3-period pharmacokinetic interaction study. In phase 1, all subjects were randomly assigned to receive 500 mg of ciprofloxacin alone and 200 mg of itraconazole alone twice daily for 7 days with a 14 day wash-out period in a crossover design. Phase 2 was performed 14 days after finishing phase 1, all subjects received 500 mg of ciprofloxacin in combination with 200 mg of itraconazole twice daily for 7 days. Ciprofloxacin and itraconazole pharmacokinetics were studied and adverse effects noted. RESULTS Ciprofloxacin significantly increased the C(max) and AUC(0 - ∞) of itraconazole by 53.13% and 82.46%, respectively. The half-life and CL of itraconazole were not changed significantly. The combination of itraconazole and ciprofloxacin could therefore result in an increase in adverse drug reactions. Conversely, itraconazole had no significant effect on the pharmacokinetics of ciprofloxacin. CONCLUSIONS Ciprofloxacin decreases the metabolism of itraconazole, most likely through inhibition of CYP3A4. The dosage of itraconazole should be reduced and its therapeutic outcome should be monitored closely when these two agents are concomitantly administered.