Sensitive determination of josamycin and rokitamycin in plasma by high-performance liquid chromatography with fluorescence detection

Rokitamycin and josamycin were successfully derivatized with dansylhydrazine in 20 min at 60°C. Rokitamycin and josamycin levels were determined in plasma after ion-pair extraction into hexane—isoamyl alcohol with lauryl sulphate and precolumn derivatization. Resolution was obtained by liquid chromatography with fluorescence detection ( 352 537 nm) in 12 min. The limit of detection was 20 ng/ml macrolide starting from 1 ml of plasma, and linearity was demonstrated between 50 and 400 ng/ml. Inter-run coefficients of variation were 10.2% at 100 ng/ml and 9.1% at 300 ng/ml. The system was reliably used for pharmacokinetic studies in plasma.