High-performance liquid chromatography of nalbuphine, butorphanol and morphine in blood and brain microdialysate samples: Application to pharmacokinetic/pharmacodynamic studies in rats

A rapid and sensitive assay for quantification of nalbuphine, butorphanol and morphine in blood (50 mu L) and brain microdialysate (similar to 40 mu L) samples was developed. Blood samples were extracted with ethyl acetate. Analysis was performed with high-performance liquid chromatography (HPLC) coupled to an electrochemical detector. The mobile phase was a mixture of 0.1 M sodium phosphate buffer, methanol and octane-sulfonic acid with ratio and pH depending on compound and matrix. The limits of quantification in blood samples were 25, 50 and 25 ng/mL for nalbuphine, butorphanol and morphine, respectively and 0.5 ng/mL for morphine in microdialysate samples. Based on sample volume, sensitivity and reproducibility, these assays are particularly suitable for pharmacokinetic/pharmacodynamic studies in rodents. (c) 2005 Elsevier B.V. All rights reserved.