Journal of the Medical Association of Thailand Vol 93, No 7:JULY 2010 0125-2208 93 7 2010 Jul Comparative Study of Pharmacokinetics/ Pharmacodynamics of Ciprofloxacin between 400 mg Intravenously Every 8 h and 400 mg Intravenously Every 12 h in Patients with Gram Negative Bacilli Bacteremia 784 EN Phanvasri Saengsuwan Sutep Jaruratanasirikul Monchana Jullangkoon Nanchanit Aeinlang Original Article To compare the ratio of the area under the concentration-time curve at 24 hours to the minimum inhibitoryconcentration value (24-h AUC/MIC) of ciprofloxacin between 400 mg intravenously every 8 h and 400 mg intravenouslyevery 12 h. A prospective, randomized, two-way crossover study of 10 patients with gram-negative bacillibacteremia was conducted. All patients were randomized to receive ciprofloxacin in both regimens consecutively: (i) 400 mgintravenously every 8 h for four doses; (ii) 400 mg intravenously every 12 h for four doses. Ciprofloxacin pharmacokineticstudies were carried out after the start of both regimens. For the ciprofloxacin 400 mg intravenously every 8 h regimen, the 24-h AUC/MIC at MICs of 0.5 and 1 μg/ml were218.63 + 78.75 and 109.31 + 39.37, respectively. For the ciprofloxacin 400 mg intravenously every 12 h regimen, the 24-hAUC/MIC at MICs of 0.5 and 1 μg/ml were 144.07 + 57.02 and 72.03 + 28.51, respectively. After 14 days of ciprofloxacintreatment, the gram-negative bacilli infections were eradicated in all patients. Moreover, during both regimens, no adverseevents related to the use of ciprofloxacin were observed. Both ciprofloxacin 400 mg every 8 h and 400 mg every 12 h regimens can provide good coverage for pathogenswith the susceptibility breakpoint of ciprofloxacin with an MIC of 0.5 μg/ml. For pathogens with an MIC of 1.0 μg/ml, onlyciprofloxacin 400 mg every 8 h regimen can provide a 24-h AUC/MIC ratio greater than 100. Ciprofloxacin Pharmacokinetic/pharmacodynamic 24-h AUC/MIC Bacteremia