title: Steady-state pharmacokinetics and BAL concentration of colistin in critically Ill patients after IV colistin methanesulfonate administration.
abstract: BACKGROUND
  Infections caused by multidrug-resistant gram-negative bacteria have caused a resurgence of interest in colistin. To date, information about pharmacokinetics of colistin is very limited in critically ill patients, and no attempts have been made to evaluate its concentration in BAL.
  
  
  METHODS
  In this prospective, open-label study, 13 adult patients with ventilator-associated pneumonia caused by gram-negative bacteria were treated with colistin methanesulfonate (CMS) IV, 2 million International Units (174 mg) q8h, a usually recommended dose, for at least 2 days. Blood samples were collected from each patient at time intervals after the end of infusion. BAL was performed at 2 h. Colistin was measured by a selective, sensitive high-performance liquid chromatography-based method. Pharmacokinetic parameters were determined by noncompartmental analysis.
  
  
  RESULTS
  Patients received 2.19 ± 0.38 mg/kg (range, 1.58-3.16) of CMS per dose. At steady state, mean ± SD plasma colistin maximum (Cmax) and trough (Ctrough) concentrations were 2.21 ± 1.08 and 1.03 ± 0.69 μg/mL, respectively. Mean ± SD area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8)), apparent elimination half-life, and apparent volume of distribution were 11.5 ± 6.2 μg × h/mL, 5.9 ± 2.6 h, and 1.5 ± 1.1 L/kg, respectively. Cmax/minimum inhibitory concentration (MIC) ratio and AUC(0-24)/MIC ratio (MIC = 2 μg/mL) were 1.1 ± 0.5 and 17.3 ± 9.3, respectively. Colistin was undetectable in BAL. Nephrotoxicity was not observed.
  
  
  CONCLUSIONS
  Although the pharmacodynamic parameters that better predict the efficacy of colistin are not known in humans, in critically ill adult patients the IV administration of CMS 2 million International Units (174 mg) q8h results in apparently suboptimal plasma concentrations of colistin, which is undetectable in BAL. A better understanding of the pharmacokinetic-pharmacodynamic relationship of colistin is urgently needed to determine the optimal dosing regimen.
authors.affiliation: Direzione Scientifica, Fondazione IRCCS Policlinco S. Matteo 27100 Pavia, Italy. r.imberti@smatteo.pv.it
authors.forename: Roberto
authors.initials: R
authors.lastname: Imberti
authors.forename: Maria
authors.initials: M
authors.lastname: Cusato
authors.forename: Paola
authors.initials: P
authors.lastname: Villani
authors.forename: Livio
authors.initials: L
authors.lastname: Carnevale
authors.forename: Giorgio A
authors.initials: GA
authors.lastname: Iotti
authors.forename: Martin
authors.initials: M
authors.lastname: Langer
authors.forename: Mario
authors.initials: M
authors.lastname: Regazzi
mesh_terms: D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry*; D003091:Colistin / Q000493:pharmacokinetics* / Q000627:therapeutic use; D016638:Critical Illness; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D005500:Follow-Up Studies; D006090:Gram-Negative Bacteria / Q000187:drug effects; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis / Q000188:drug therapy*; D006801:Humans; D007262:Infusions, Intravenous; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D053717:Pneumonia, Ventilator-Associated / Q000175:diagnosis / Q000188:drug therapy* / Q000401:mortality; D011446:Prospective Studies; D015996:Survival Rate; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D003091:Colistin