20 l of supernatant was diluted ten times with methanol sterilized water and 5 l was used for lc ms ms analysis 5 data analysis the measured signal values obtained from lc ms ms analysis were logarithmically transformed to give the amounts of cyp2e1 standard metabolite 6 hydroxy chlorzoxazone pmol using the control group as baseline with inhibition set at 0 the inhibition of cyp2e1 was then calculated by the following equation inhibition u2062 u2062 of u2062 u2062 cyp u2062 u2062 2 u2062 e u2062 u2062 1 u2062 1 u2062 the u2062 u2062 amount u2062 u2062 of u2062 u2062 6 u2062 u2062 oh u2062 u2062 czx u2062 u2062 in experimental u2062 u2062 group control u2062 u2062 6 u2062 u2062 oh u2062 u2062 czx the inhibition of cyp 2e1 of positive control ddtc is shown in table 2 and according to table 2 ddtc can inhibit up to 87 56 of cyp 2e1 activity at concentration 100 u03bcm inhibition of cyp 2e1 by chinese herbal ingredients was shown in table 3 and suggested that different guiding drugs have different effects on cytochrome p450 cyp 2e1 activity at various concentrations 66 u03bcm 33 u03bcm 16 5 u03bcm and nordihydroguaiaretic acid at 66 u03bcm showed the best inhibition activity 96 98 u00b1 0 19 cyp 2e1 inhibition by excipients was shown in table 4 and indicated that different excipients have different effects on cytochrome p450 cyp 2e1 activity at various concentrations 0 167 0 08 0 042 w v and 0 167 brij.