OBJECTIVES: Several studies have described a remarkable interaction between Meropenem and Valproic acid (VPA). However, there’s no analysis has been conducted evaluating the influence of different carbapenems on VPA blood level. We sought to analyze the influence of Biapenem on VPA blood concentration and the risk of seizures. METHODS: We retrospectively collected the patients who concomitant administrated of VPA and Biapenem, Meropenem as the control group::Biapenem 37 cases and Meropenem 48 cases. Recorded the information as follows: general clinical data, medication, VPA concentration, seizures and treatment and so on. RESULTS: Both of Biapenem and Meropenem significantly decreased the VPA blood level . The lowest concentrations in Biapenem group were higher than Meropenem group(P= 0.046). The mean decrease of VPA level in Biapenem group was also less than Meropenem group (70.65±9.64% vs 78.83±8.78%,P=0.01). There were six patients treated with Biapenem and Meropenem at different times of infection during taken the VPA. The lowest VPA concentrations were also higher when concomitant administrated of Biapenem compared to Meropenem . The rate of seizures in Biapenem group and Meropenem group were 29.73% and 35.42% respectively(P=0.749). Most physicians discontinued the carbapenems, increased the VPA dose or added other antiepileptic drugs. CONCLUSIONS: The extent of decrease in VPA serum concentrations was greater in meropenem-treated patients than in biapenem-treated cases. But Biapenem also decreased the VPA blood level as 70% and increased the risk of seizures , concomitant using of these medications should be avoided.