Pharmacokinetics and bioavailability of cinnamic acid after oral administration of ramulus cinnamomi in rats

The pharmacokinetics of cinnamic acid (CA) after oral administration of Decoction of Ramulus Cinnamomi (RC) 7.4 g/kg [containing CA 7.62x10(-5) mol/kg and cinnamaldehyde (CNMA) 1.77x 10(-5) mol/kg], was compared with that after oral administration of pure CA 7.62x10(-5) mol/kg in rats. Plasma concentrations of CA and hippuric acid (HA) were determined by HPLC. Pharmacokinetic parameters were calculated from the plasma concentration-time data. CA was quickly absorbed and then metabolized mainly into HA. The AUC((0-1)) and AUC((0-infinity)) of CA were higher in RC group than those in pure CA group and the bioavailability of CA from RC was higher than that from pure CA. After ig administration of 3.79x10(-4) mol/kg, CNMA was at least partially metabolized into CA in stomach and small intestine and almost completely metabolized into CA in liver before it is absorbed into blood in rats. The results showed that plasma CA in RC group might partly come from transformation of CNMA in RC.