Laser light scattering bioassay for 1-beta-D-arabinofuranosylcytosine (ARA-C, NSC-63878).

A bioassay method for the estimation of ara-C in biological samples which utilizes laser light scattering from suspensions of drug-sensitive bacteria has been developed. The species employed in the assay was Streptococcus faecium var. durans resistant to methotrexate and 6-mercaptopurine. In less than four hours, serum and urine levels of ara-C can be reproducibly measured using the method. A sample volume of 0.1 ml containing 30 ng/ml may be assayed with a precision of +/-10 percent. The present studies further confirm the utility of the method as a rapid and relatively inexpensive assay methodology of broad application. Time variations of drug serum levels and urinary excretion rates in dogs are compared via the differential light scattering (DLS) assay, standard disc diffusion assay, and radiosotopic assay. The results obtained by the various methods are in excellent agreement.