Abstract: AIM: An LC-MS method was developed and validated for the analysis of Guanfu Base A in dog plasma to support the pharmacokinetic study. METHODS: Blood was withdrawn at different times and absolute bioavailability was studied by LC-MS at dosage of 4 mg/kg in 6 beagle dogs. RESULTS: The pharmacokinetic of Guanfu Base A in Beagle dogs fits best to two compartment model with AUC_{0-48 h}, C_max, t_max and half life t_1/2 of (17623.9±7006.4) ng·mL^-1·h, (1988±972)ng/mL, (0.8±0.7) h, and (11.2±1.6) h, respectively. Compared with i.v administration, the absolute bioavailability of Guanfu Base A was(99.0±11.2)%, with absorption rate (K₀₁)at (7.563±4.612)/h.CONCLUSION: After oral administration, GFA can be rapidly and completely absorbed by Beagle dogs, which suggested that oral administration of Guanfu Base A could be a substitute way for anti-arrhythmic treatment.

Key words: Guanfu Base A hydrochloride, LC-MS, Pharmacokinetics, Beagle dogs