Abstract: AIM: To compare the central nervous system effect of diazepam on Chinese Han subjects and Chinese Tong subjects. METHODS: Ten subjects of healthy male Tong and ten subjects of healthy male Han were given single oral doses of placebo,7.5 mg diazepam or 15 mg diazepam in a double-blind randomized crossover study. The plasma levels of diazepam, the Digit Symbol Substitution Test (DSST) and the electroencephalographic (EEG) were determined at 0.5, 1, 1.5, 2, 3, and 5 h after administration. RESULTS: The plasma concentra-tions of diazepam in Han subjects were significantly higher than that in Tong subjects at 1-1.5 hours after adminis-tration of 7.5 mg diazepani and at 0.5-1.5 h after ad-ministration of 15 mg diazepam, but they were significant-ly lower at 3-5 houi-s after administration of 15 mg diaze-pam.However, there was no statistical difference between the two ethnic groups in the area under the 5-hour con-centration-time curve after administration of both doses. The decrement of DSST were significantly lower in Han subjects than that in Tong subjects at 1-1.5 h and 3-5 h after administration of 15 mg diazepam, but there was no statistical difference when the decrement of DSST were corrected by the plasma concentrations of diazepam. The individual concentration-response curves were used to cal-culate the concentration of diazepam required to produce a 50 % increase in the percentage of EEG amplitude falling in the range of 12.8 to 31.2 Hz, and there was no signif-icant difference between the Han subjects (543.8±371.7 μg·L^-1) and Tong subjects (547.0±590.7 μg·L^-1) (P>0.05). CONCLUSION: The central nervous system effect of diazepam in Han subjects is simi-lar with that in Tong subjects.

Key words: diazepam, electroencephalographic, psychomotor performance test, pharmacodynainics