An HPLC method for the determination of granisetron in guinea pig plasma

A high-performance liquid chromatographic (HPLC) method for the determination of granisetron (GRN) in guinea pig plasma has been developed. Guinea pig plasma spiked with GRN was microfiltered, and the recovered filtrate was directly injected onto the column without any further cleanup procedures. Separation was achieved on a spherical silica column and GRN was detected at 305 nm. Approximately 800-900 injections were made without any evidence of column deterioration. For the standard curves, correlation coefficients ranged from 0.9978-0.9999, and the percent standard deviation (%SD) from the mean area under the curve (AUC) was calculated to be less than 10% for all concentrations, except for the lowest concentration (0.325 ng/microL, 11.3%). Between-day and within-day coefficients of variation (%CV) ranged from 4.9 to 9.5% and 3.6 to 7.6%, respectively. Percent errors for within-day test plasma samples were not greater than 8.2% of the expected concentration for all samples except for 1.125 ng/microL (-14.6%). The limit of sensitivity was found to be 0.019 ng/microL. Estimated recovery of GRN in the microfiltrate was calculated to be 58-59% and 78-81% in plasma and water, respectively. Stability studies indicated that repeated refrigeration and warming (for six days) of microfiltered GRN plasma samples produced no changes in GRN concentrations from day to day. However, microfiltered GRN plasma samples that were repeatedly frozen and thawed demonstrated erratic concentration changes from day to day. The precision, accuracy, and small sample requirements of this method indicate its utility for pharmacokinetic studies in small animals where sample volume may be restrictive.