OBJECTIVE:To investigate the effects of gender

age

weight

drug combination and concomitant disease on serum drug concentration/dose ratio（C/D） of valproic acid in patients with epilepsy.METHOD:77 patients with epilepsy who were monitored for serum drug concentration of valproic acid in a certain hospital from May2018 to Aug.2019 were retrospectively analyzed.Information including gender

age

weight

drug combination

concomitant disease

daily dose and serum drug concentration were entered into the Excel table to calculate C/D values.SPSS 22.0 was adopted to conduct statistical analysis.RESULTS:The C/D values of patients aged <6 years

6-<12 years

12-< 18 years

18-< 60 years

≥60 years were respectively（192.80 ± 106.44）

（113.37 ± 53.36）

（64.77±33.67）

（60.34±23.82） and（84.80±21.50） ng·d/（mg·ml）

with statistically significant differences（P<0.05）.The C/D values of patients weighed <22 kg

22-35 kg and >35 kg were respectively（176.41±114.75）

（134.61±43.76） and（63.12±27.26） ng·d/（mg·ml）

with statistically significant differences（P<0.05）.Gender

drug combination and concomitant disease had no effects on the C/D values.CONCLUSIONS:Children age <12 years old（especially<6 years old） and patients weighed ≤35 kg need to reduce the dose of valproic acid appropriately to prevent adverse drug reactions.