Abstract: Previous studies showed species difference of helicid metabolic process between human and rat. Plasma protein binding rate of drugs is an important process for determining their overall distribution,excretion,activity and toxicity. The aim of this study was to assess the effects of helicid plasma protein binding rates in species difference using equilibrium dialysis. Liquid chromatography-mass spectrometry analysis was carried out and was optimized against some influencing factors during experimental procedures. The method developed in this research was validated to be specific,sensitive and accurate. The binding fractions were about 10.33%-11.03% for rats and 10.60%-10.98% for human within four concentration levels. According to our results,it was concluded that the PK parameters differences between human and rat were not due to plasma protein binding. This was the study of helicid plasma protein binding reported for the first time.

Key words: plasma protein binding, helicid, LC-ESI-MS, species differences