Basic Study of Drug-Drug Interaction between Memantine and the Traditional Japanese Kampo Medicine Yokukansan

Several basic pharmacokinetic and pharmacological studies were conducted as part of a group of studies to clarify the drug-drug interaction (DDI) between memantine (MEM), a drug used to treat Alzheimer’s disease, and yokukansan (YKS), a traditional Japanese Kampo medicine used to treat behavioral and psychological symptoms of dementia. The pharmacokinetic studies showed that there were no statistically significant differences in MEM concentrations in the plasma, brain, and urine between mice treated with MEM alone and with MEM plus YKS. Regarding candidate active ingredients of YKS, there were also no statistically significant differences in concentrations of geissoschizine methyl ether in the plasma and brain, urine, glycyrrhetinic acid in the plasma, and isoliquiritigenin in the urine, in mice treated with YKS alone or with MEM plus YKS. The pharmacological studies showed that isoliquiritigenin, which has an N-methyl-d-aspartic acid (NMDA) receptor antagonistic effect, did not affect the inhibitory effect of MEM on NMDA-induced intracellular Ca(2+) influx in primary cultured rat cortical neurons. Moreover, YKS did not affect either the ameliorative effects of MEM on NMDA-induced learning and memory impairment, or the MEM-induced decrease in locomotor activities in mice. These results suggest that there is probably no pharmacokinetic or pharmacological interaction between MEM and YKS in mice, but more detailed studies are needed in the future. Our findings provide important information for future studies, to clarify the DDI more regarding the efficacy and safety of combined use of these drugs in a clinical situation.