Determination of unbound cimetidine in rat blood by microdialysis and liquid chromatography

A simple and sensitive method for the determination of protein-unbound cime tidine in rat blood was developed, based on the sampling method of microdia lysis. The microdialysis probe was inserted into the jugular vein/right atr ium of male Sprague-Dawley rats. Cimetidine (10 mg/kg, i.v.) was then admin istered via the femoral vein. Separation was achieved on a LiChrosorb RP-ls column with a mobile phase consisting of acetonitrile-100 mM monosodium ph osphate, pH 3.0 (22:78, v/v). The UV detector wavelength was set at 228 nm. The detection limit of cimetidine was 50 ng/mL. The in vivo recovery of mi crodialysate for cimetidine at 0.5 and 1 mu g/mL were 73 +/- 8% and 74 +/- 8%, respectively (n=5). Intra- and inter-assay accuracy and precision of th e analyses were less than or equal to 10% in the range of 0.05 through 10 m u g/mL. Pharmacokinetic analysis of results obtained using such a microdial ysis-chromatographic method indicated unbound cimetidine in the rat fitted best to a biexponential decay model.