Pharmacokinetics and Brain Distribution of Tetrahydropalmatine and Tetrahydroberberine after Oral Administration of DA-9701, a New Botanical Gastroprokinetic Agent, in Rats

DA-9701, a new botanical gastroprokinetic agent, has potential for the management of delayed gastric emptying in Parkinson's disease if it has no central anti-dopaminergic activity. Therefore, we examined the pharmacokinetics of DA-9701 components having dopamine D-2 receptor antagonizing activity, tetrahydropalmatine (THP) and tetrahydroberberine (THB), following various oral doses (80-328 mg/kg) of DA-9701. The distribution of THP and THB to the brain and/or other tissues was also evaluated after single or multiple oral administrations of DA-9701. Oral administration of DA-9701 yielded dose-proportional area under the plasma concentration-time curve (AUC(0-8h)) and maximum plasma concentration (C-max) values for THP and THB, indicating linear pharmacokinetics (except for THB at the lowest dose). THP and THB's large tissue-to-plasma concentration ratios indicated considerable tissue distribution. High concentrations of THP and THB in the stomach and small intestine suggest an explanation for DA-9701's potent gastroprokinetic activity. The maximum concentrations of THP and THB in brain following multiple oral DA-9701 for 7d (150mg/kg/d) was observed at 30min after the last oral DA-9701 treatment: 131-1 +/- 67.7ng/g for THP and 6.97 +/- 4.03ng/g for THB. Although both THP and THB pass through the blood-brain barrier, as indicated by brain-to-plasma concentration ratios greater than unity (approximately 2-4), oral administration of DA-9701 at the effective dose in humans is not expected to lead to sufficient brain concentrations to exert central dopamine D-2 receptor antagonism.