Background Chronic intermittent hypoxia (CIH) has been associated with abnormalities in the liver,which is the most important organ for drug metabolism.This study aimed to investigate the effect of CIH on theophylline metabolism in mouse liver.Methods Eight C57BL/6J mice were exposed to CIH for 12 weeks.Eight C57BL/6J mice were exposed to room air as a control group.Serum levels of alanine aminotransferase and aspartate aminotransferase were measured.Liver histology was observed by light and electron microscopy.Total hepatic cytochrome P450 concentration was measured.Hepatocytes were isolated and incubated with 15 mg/ml theophylline for four hours.After incubation,the theophylline concentration in the supatant was measured and the theophylline metabolism rate was calculated.Results CIH did not affect the serum transaminase levels.Livers from mice exposed to CIH showed hepatocellular edema,and liver cells had fuzzy rough endoplasmic reticulum under the electron microscope.The theophylline metabolism rate was significantly inhibited by CIH compared with controls; (16.60±2.43)％ vs.(21.58±4.52)％ (P=0.02).The total liver cytochrome P450 concentration in the CIH group was significantly lower than in the control group;(0.83±0.08) vs.(1.13±0.21) mol/mg microsomal protein (P=0.004).Conclusion CIH decreases theophylline metabolism by mouse hepatocytes,which may correlate with the downregulation of cytochrome P450 expression by CIH.