Determination of trace cantharidin in plasma and pharmacokinetic study in beagle dogs using gas chromatography-mass spectrometry.

The blister beetle is traditional Chinese medicine that was first discovered and used as anticancer drug in China, and cantharidin proved to be its principal active ingredient. Cantharidin-based pharmaceutical preparations are now widely used in clinics in China with good therapeutic efficacy. As a toxic anticancer drug, the therapeutic dose of cantharidin is low, and no method to determine the blood cantharidin concentration under the therapeutic dose has so far been reported. Here, we present a simple, sensitive, and reliable gas chromatography-mass spectrometry (GC-MS) method to monitor the plasma cantharidin and perform the pharmacokinetic study of cantharidin in beagle dogs. After protein precipitation by hydrochloric acid, a liquid-liquid extraction procedure using ethyl acetate was applied to extract cantharidin from plasma. An elastic quartz capillary GC column DB-5MS was used in GC-MS, the temperature was kept at 60 degrees C for 1 min, then increased to 220 degrees C at the rate of 6 degrees C/min, held there for 1 min, and then to 280 degrees C at the rate of 20 degrees C/min, held for 3 min. The extraction recovery was over 80% for all the tested specimens. The linearity ranged from 2.14 to 314.2 ng/mL, the intra- and interday precisions were both below 20%, the limit of detection was 0.5 ng/mL, and the limit of quantification was 2.14 ng/mL. Cantharidin in plasma proved to be stable during the whole period of storage, treatment, and analysis. Cantharidin demonstrated as one-compartment model after i.v. administration with an elimination half-life of 0.69 +/- 0.03 h and area under curve of 204 +/- 24 h.ng/mL. This GC-MS assay proved to have high precision, accuracy, reliability, and sensitivity, and it was suitable for determination of trace cantharidin in plasma.