Rapid analysis of ranitidine in biological fluids and determination of its erythrocyte partitioning.

A reversed-phase ion-pair high-performance liquid chromatographic assay is described for the rapid and sensitive quantitation of the H2-receptor antagonist ranitidine in human plasma and urine. The method involves a single-step extraction of the alkalinized sample with methylene chloride and analysis of the evaporated extract on a cyano column. Detection was performed by ultraviolet absorbance monitored at 318 nm. The overall run time of the assay was 5 min at a flow-rate of 2.0 ml/min. The limit of sensitivity was 1 ng/ml ranitidine in human plasma. Urine and plasma samples collected from a subject after administration of an oral dose of 150 mg of ranitidine were analyzed by this method. Furthermore, the procedure was applied to determine the red blood cell partition coefficient of ranitidine in a concentration range up to 10 micrograms/ml.