Direct determination of substituted azepinoindole enantiomers in rat plasma using silica stationary phase and beta-cyclodextrin as a mobile phase additive.

DU 124884 is a racemic serotonin receptor agonist in an early stage of drug development. DU 124884 and its potential N-desmethyl metabolite, KC 9048, both contain a single chiral center. A direct enantioselective HPLC assay was developed and validated to quantify DU 124884 and KC 9048 in rat plasma. The drug and metabolite enantiomers were extracted from plasma and separated using silica stationary phase with an aqueous mobile phase containing beta-cyclodextrin (beta-CD), triethylamine, and 2-methyl-2-propanol. A variable wavelength detector was used to monitor absorbance at 231 nm. The assay calibration range was from 100 to 5000 ng/mL. Quality control sample precision (< or = 9% RSD) and accuracy (+/-10% error) were satisfactory for all four analytes (n = 12). The method was used to assess drug exposure during a pilot toxicology study in rats. Toxicokinetic study animals were dosed subcutaneously for 15 days at 0, 2.5, 10, and 40 mg of DU 124884.HCl kg-1 day-1. Blood was collected on the last day of dosing between 22 min and 4 h and 13 min after the last dose. The samples showed (+/-)-DU 124884 isomer ratios ranging from 1.1 to 1.3. These data suggest that DU 124884 undergoes stereoselective metabolism in rats. Levels of the N-desmethyl metabolite enantiomers were < 100 ng/mL.