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Rifampicin is oxidized with hydrogen peroxide to a product that is fluorescent in alkaline solutions. Maximum fluorescence is measured at 480 nm with an excitation wavelength of 370 nm. The lower limit of detection of rifampicin in water is 0.1 μg/ml. A microbiological assay with Staphylococcus aureus 560 as the assay organism verified the reliability of the fluorometric assay. The fluorametric and microbiological assays were applied to the estimation of rifampicin in serum and were used to obtain concentration-time data for dogs that had been treated orally with 10 mg/kg rifampicin. Half-life of rifampicin in the dog was 8 h.

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As determined by a colorimetric assay measuring parent compounds plus ether-extractable nitroso-containing metabolites, N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) disappeared more rapidly than N-(2-chloroethyl)-N'cyclohexyl-N-nitrosourea (CCNU) and N-(2-chloroethyl)-N'-(4-transmethylcyclohexyl)-N-nitrosourea (MeCCNU) and their products from the tissues of mice injected IV. Assay of selected samples by high-pressure liquid chromatography revealed that the colorimetric assay for BCNU was specific in that the two assays gave equivalent results. Following IV-injections of CCNU and MeCCNU, however, levels of the parent compounds decreased much more rapidly than the total, color-producing material. Of seven tissues, the largest Cxt values for BCNU, as determined by the colorimetric assay, were noted for blood (442 microgram-min/ml) and large intestine (285 microgram-min/g). Liver (29 microgram-min/g) had the lowest Cxt value, reflecting rapid metabolism of the compound by this organ. Color-producing material related to CCNU disappeared from the solid tissues of mice in a manner generally parallel to that for blood. Of the Cxt values for this compound and its products, those for lung (1753 microgram-equivalents-min/g), kidney (1633 microgram-equivalents-min/g), and small intestine (1557 microgram-equivalents-min/g) were highest. Consistent with its slower rate of metabolism, MeCCNU and its color-producing metabolites remained in most tissues of mice for 12 h following injection. Except for brain (1434 microgram-equivalents-min/g), Cxt values for this nitrosourea and its metabolites in tissues were higher than those of blood (5485 microgram-equivalents-min/ml), with kidney (15,324 micrograms-equivalents-min/g), liver (12,921 microgram-equivalents-min/g), and large intestine (11,501 microgram-equivalents-min/g) being highest. For each nitrosourea, a fair correlation was observed between the Cxt values for tissues and the toxic and/or antitumor effects at those sites.