More than 80 patients at the University of Pittsburgh Medical Center have been infected with Pseudomonas aeruginosa, lacking susceptibility to all commercially available antibiotics except "colistin". This antibiotic was developed in the 1960s and preliminary pharmacokinetic studies were performed at that time. Dosing recommendations, on the basis of these pharmacokinetic studies, are listed in the drug's product information. However, there are no dosing recommendations for patients requiring renal replacement therapy (either intermittent hemodialysis or continuous venovenous hemofiltration). Furthermore, the science of antibiotic dosing ("pharmacodynamics") has changed significantly since the 1960s and it is quite possible that the dosing recommendations listed in the product information are not optimal. Furthermore, even though physicians refer to "colistin" administration, the only intravenous form of the drug is colistin methanesulfonate (CMS). CMS is converted in the body to colistin.

Both CMS and colistin have different pharmacokinetic and antimicrobial activities. For this reason, we, the investigators at the University of Pittsburgh, are performing a pilot study of the pharmacokinetics of intravenous CMS/colistin in patients requiring this antibiotic for clinical purposes.

Plasma concentrations will be determined around a CMS/colistin dose once the drug has reached steady state. Concentrations in pulmonary epithelial lining fluid will also be determined in patients with pneumonia. Microbiologic and clinical endpoints will be determined and will be correlated with these concentrations. The measurement of CMS and colistin levels will be determined by a laboratory in Australia which developed these assays. A submission is being made to the National Institutes of Health (NIH) for funding of a multicenter study which will address this research question with a greater sample size. The study proposed here is a pilot study in order to prove the feasibility of the research approach and to provide preliminary data for the NIH proposal.