In order to prepare samples for HPLC analysis with maximum drug recovery and impurity elimination, a revised method for the extraction and purification of a target substance from plasma was developed and applied in a pharmacokinetic study with Nimodipine as a model drug. After protein precipitation of a plasma sample using pure methanol and evaporation of the supernatant to dryness, methanol of various concentrations from 10% to 100% were used to dissolve the remaining residues with the goal of maximizing drug recovery and impurity elimination. Through rigorous screening with HPLC peaks from residual impurity and recovered drug as the criteria, a methanol concentration of 30% was chosen. The standard curve was linear （r2〉 0.999） over the range of 2-160 ng/mL with a limit of quantification （LOQ） of 2 ng/mL. Intra- and inter-day precision values were below 15%, and the accuracy ranged from -1.70% to 5.88% at all three quality control （QC） levels. The wavelength of maximum absorption was 238 nm, and a smaller LOQ value of 2 ng/mL was achieved compared with the reported method. The revised method was successfully applied in a pharmacokinetic study of Nimodipine in rats and sample preparations of lidocaine hydrochloride.
The previous investigation has proved that their existed pharmacokinetic difference between the different crystal forms of the polymorphic drugs after oral administration.However,no systemic investigations have been made on the change of this pharmacokinetic difference,resulted either from the physiological or from the pathological factors.In this paper,we used polymorphic nimodipine(Nim) as a model drug and investigated the effect of age difference(2- and 9-month old) on the pharmacokinetics after oral delivery in rats.As the results shown,for L-form of Nim(L-Nim),the AUC0–24 hin 2-month-old rats was 343.68747.15 ng h/m L,which is 23.36% higher than that in 9-month-old rats.For H-form of Nim(H-Nim),the AUC0–24 hin 2-monthold rats was 140.91719.47 ng h/m L,which is 54.64% higher than that in 9-month-old rats.The AUC0–24 h ratio between H-Nim and L-Nim was 2.44 in 2-month-old rats and 3.06 in 9-month-old rats.Since age difference could result in unparallelled change of the absorption and bioavailability of the polymorphic drugs,the results in this experiment are of value for further investigation of crystal form selection in clinical trials and rational clinical application of the polymorphic drugs.
