Pharmacokinetic Study of Borneol and Menthol in Rats after Oral Administration of Qingyan Drop Pills

Both borneol and menthol are bioactive substances derived from Chinese herbal medicines. In order to understand the pharmacokinetics of borneol and menthol in Qingyan drop pills, a rapid, sensitive, and simple gas chromatographic (GC) method with flame ionization detection (FID) was developed for the simultaneous determination of borneol and menthol in rat plasma. Sample preparations were carried out by liquid-liquid extraction (LLE) with an internal standard solution of naphthalene. The analytes and internal standard (IS, naphthalene) were separated well on an HP-1 capillary column. The pharmacokinetic parameters were estimated by a compartmental method using the Phoenix WinNonlin software program (Version 6.0). The standard curves were linear over a wide concentration range of 2.5-50.0 ng/mu L (r = 0.9963), 8.7-62.2 ng/mu L (r = 0.9994) for both borneol and menthol in plasma, respectively. The limits of quantification (LOQ) of borneol and menthol in plasma were 2.4 ng/mu L and 5.0 ng/mu L, respectively. The intraday precisions for borneol and menthol were < or = 10.0% R. S. D. at the LOQ and < or = 6.0% at higher concentrations. The average value of C-max was 18.97 +/- 2.71 ng/mu L with a T-max at 20.00 +/- 0.00 min for borneol after oral administration of the drop pills; for menthol, the average value of C-max was 79.02 +/- 11.40 ng/mu L with a T-max at 25.00 +/- 4.40 min. This validated assay method was successfully applied to a pharmacokinetic study of borneol and menthol after oral administration of Qingyan drop pills in rat. The results showed that the kinetics of borneol and menthol can be described by an open one-compartment model. The pharmacokinetic parameters provide some information for clinical administration of Qingyan drop pills.