Dose-ranging pharmacokinetics of colistin methanesulphonate (CMS) and colistin in rats following single intravenous CMS doses

Objectives The aim of this study was to evaluate the effect of colistin methanesulphonate (CMS) dose on CMS and colistin pharmacokinetics in rats. Methods Three rats per group received an intravenous bolus of CMS at a dose of 5, 15, 30, 60 or 120 mg/kg. Arterial blood samples were drawn at 0, 5, 15, 30, 60, 90, 120, 150 and 180 min. CMS and colistin plasma concentrations were determined by liquid chromatography–tandem mass spectrometry (LC-MS/MS). The pharmacokinetic parameters of CMS and colistin were calculated by non-compartmental analysis. Results Linear relationships were observed between CMS and colistin AUCs to infinity and CMS doses, as well as between CMS and colistin Cmax and CMS doses. Conclusions CMS and colistin pharmacokinetics were linear for a range of colistin concentrations covering the range of values encountered and recommended in patients even during treatment with higher doses.