The purpose of this study was to define the pulmonary and systemic pharmacokinetics of
colistin methanesulfonate (CMS) and formed
colistin following intravenous (i.v.) and inhaled administration in
cystic fibrosis (CF) patients. Six CF subjects were administered nebulized CMS doses of 2 and 4 million IU and an i.v. CMS infusion of 150 mg of
colistin base activity. Blood plasma, sputum, and urine samples were collected for 12 to 24 h postdose. To assess the tolerability of the
drug, lung function tests, blood serum
creatinine concentrations, and adverse effect reports were recorded. All doses were well tolerated in the subjects. The pharmacokinetic parameters for CMS following i.v. delivery were consistent with previously reported values. Sputum concentrations of formed
colistin were maintained at <1.0 mg/liter for 12 h postdose. Nebulization of CMS resulted in relatively high sputum concentrations of CMS and formed
colistin compared to those resulting from i.v. administration. The systemic availability of CMS was low following nebulization of 2 and 4 million IU (7.93% ± 4.26% and 5.37% ± 1.36%, respectively), and the plasma
colistin concentrations were below the limit of quantification. Less than 2 to 3% of the nebulized CMS dose was recovered in the urine samples in 24 h. The therapeutic availability and drug targeting index for CMS and
colistin following inhalation compared to i.v. delivery were significantly greater than 1. Inhalation of CMS is an effective means of targeting CMS and formed
colistin for delivery to the lungs, as high lung exposure and minimal systemic exposure were achieved in CF subjects.