Determination of Alendronate in Low Volumes of Plasma by Column-Switching High-Performance liquid Chromatography Method and Its Application to Pharmacokinetic Studies in Human Plasma

A sensitive and simple column-switching high-performance liquid chromatographic (HPLC) method with fluorescence detection was developed for the determination of alendronate in human plasma. Alendronate and pamidronate (internal standard, IS) in plasma including Na(2)EDTA were precipitated with sodium hydroxide and calcium chloride after deproteinization using 10% trichloroacetic acid solution. The precipitated alendronate and IS were reconstituted by sodium citrate and citric acid and then derivatized with 9-fluorenylmethyl chloroformate. The resulting solution was injected onto an HPLC system consisting of a pretreatment column and an analytical column, which were connected with a six-port switching valve. The assay was linear in the concentration range of 2-100 ng/mL in 1 mL of plasma with high precision and accuracy, and the limit of detection was 0.5 ng/mL. It was successfully applied to evaluate the pharmacokinetic parameters of alendronate in human volunteers following single oral administration. The mean value of maximum alendronate plasma concentration (C(max)) was 37.69 ng/mL, and the mean time to reach the C(max) (T(max)) was 1.08 h. The area under the plasma concentration-time curve (AUC) and elimination half-life (T(1/2)) were 106.48 ng/mL/h and 1.66 h, respectively.