[Quantitative analysis of rifampicin and 25-desacetylrifampicin in the plasma using high performance liquid...

A procedure for determination of rifampicin and 25-desacetylrifampicin in plasma by HPLC was developed. The plasma proteins are precipitated by acetonitrile and the supernatant layer (50 microliters) is used for the assay under isocratic conditions on an analytical column 250 x 4.6 mm in size containing the reversed phase sorbent (C18). The size of the precolumn is 50 x 4.6 mm. An UV detector (at lambda 335 nm) is used. For preparing the mobile phase 630 ml of methanol and 370 ml of 0.058 M sodium nitrite solution are mixed. The flow rate of the mobile phase is 40.7 ml/min. The assay duration is about 10 min. The retention time is 9.6 min for rifampicin and 6.5 min for 25-desacetylrifampicin. The minimum detectable amount of the antibiotic and its metabolite is 0.10 micrograms/ml. The standard curves of rifampicin and 25-desacetylrifampicin are linear within the concentration ranges of 0.5-100 and 0.5-10 micrograms/ml respectively. The procedure is useful in studies on pharmacokinetics of rifampicin and 25-desacetylrifampicin.