Objective: Nevirapine-based therapy is associated with increased frequency of adverse events among women with CD4+cell count of 250 cells/μL or greater. We evaluated the safety of nevirapine-based antiretroviral therapy in human immunodeficiency virus (HIV)-1-infected pregnant women. METHODS: We retrospectively evaluated 23 pregnancies managed with nevirapine-based regimens from July 2001 to April 2005. The incidence of adverse events was determined and analyzed by CD4+cell count of either less than or greater than or equal to 250 cells/μL, and gestational age when nevirapine was initiated. Liver function abnormality was graded according to the National Institute of Allergy and Infectious Diseases Division of AIDS toxicity guidelines. RESULTS: Five of 23 patients (21.7%) started nevirapine-based therapy after 27 weeks of gestation. All 3 cases of adverse events occurred in this group within 6 weeks of initiating therapy and with CD4+cell count greater than 250 cells/μL. A significant difference was noted in the proportion of patients who developed toxicity while starting nevirapine in the third trimester (3/5, 60%; 95%confidence interval 14.66-94.73%) compared with those starting nevirapine earlier in pregnancy (0/18, 0%; 95%confidence interval 0.0-18.53%; P < .006). Two patients developed rash, eosinophilia, and liver function abnormality, with one developing clinical hepatitis and renal failure. A third patient had abnormal elevation of liver enzymes but was asymptomatic. CONCLUSION: The incidence of adverse events with nevirapine may be lower than previously reported (13%versus 29%) and may be primarily noted with initiating the drug late in pregnancy. Further study of nevirapine in larger cohorts of HIV-infected pregnant women is warranted to determine the relationship between nevirapine hepatotoxicity and trimester use. Objective: Nevirapine-based therapy is associated with increased frequency of adverse events among women with CD4 + cell count of 250 cells / μL or greater. We evaluated the safety of nevirapine-based antiretroviral therapy in human immunodeficiency virus (HIV) -1-infected METHODS: We retrospectively evaluated 23 pregnancies managed with nevirapine-based regimens from July 2001 to April 2005. The incidence of adverse events was determined and analyzed by CD4 + cell count of either less than or greater than or equal to 250 cells / μL, and gestational age when nevirapine was initiated. Liver function abnormality was graded according to the National Institute of Allergy and Infectious Diseases Division of AIDS toxicity guidelines. RESULTS: Five of 23 patients (21.7%) started nevirapine-based therapy after 27 weeks of gestation. All 3 cases of reverse events occurred in this group within 6 weeks of initiating therapy and with CD4 + cell count greater than 250 cells / μL. A significan t difference was noted in the proportion of patients who developed toxicity while starting nevirapine in the third trimester (3/5, 60%; 95% confidence interval 14.66-94.73%) compared with those starting nevirapine earlier in pregnancy (0/18, 0 %; 95% confidence interval 0.0-18.53%; P <.006). Two patients developed rash, eosinophilia, and liver function abnormality, with one developing clinical hepatitis and renal failure. A third patient had abnormality of liver enzymes but was asymptomatic CONCLUSION: The incidence of adverse events with nevirapine may be lower than previously reported (13% versus 29%) and may be examined noted with initiating the drug late in pregnancy. Further study of nevirapine in larger cohorts of HIV-infected pregnant women is warranted to determine the relationship between nevirapine hepatotoxicity and trimester use.