Sensitive assay for the determination of cefazolin or ceftriaxone in plasma utilizing LC

A rapid, specific and very sensitive liquid chromatographic assay using standard ultraviolet detection has been developed to measure cefazolin (CFZ) or ceftriaxone (CFX) in small samples (200 microl) of plasma using either drug as the internal standard for measurement of the other. A rapid extraction was performed using C18 bonded Sep Pak cartridges with high extraction efficiency for both drugs. The chromatographic system employed the use of a Nova-Pak C18 4-microm cartridge with a radial compression system preceded by a Guard-Pak with a C18 insert. The mobile phase consisted of an aqueous solution containing 10 mM of dibasic potassium phosphate and 10 mM cetyltrimethylammonium bromide (pH 6.5) with acetonitrile (73:27 v/v). The drug and internal standard (CFZ/CFX) were detected using a UV detector set at a wavelength of 274 nm. Assay results were linearly related to the concentration (r > 0.997) for the wide range which was examined (0.005-120 microg/ml) for either drug. We report the precision, accuracy, recovery, linearity, sensitivity and specificity of this assay. The intra-run and inter-run CV was less than 9.02%. This method is currently being used for clinical therapeutic monitoring and pharmacokinetic studies of CFZ and CFX in patients undergoing cesarean section.