Joel Emery1, Neora Pick2, Edward J Mills3, Curtis L Cooper11The Ottawa Hospital Division of Infectious Diseases, University of Ottawa, Ottawa, Canada; 2Oak Tree Clinic, BC Women’s Hospital, Vancouver, Canada; 3Faculty of Health Sciences, University of Ottawa, Ottawa, CanadaObjective: The influence of biological sex on human immunodeficiency virus (HIV) antiretroviral treatment outcome is not well described in HIV–hepatitis C (HCV) coinfection.Methods: We assessed patients’ clinical outcomes of HIV–HCV coinfected patients initiating antiretroviral therapy attending the Ottawa Hospital Immunodeficiency Clinic from January 1996 to June 2008.Results: We assessed 144 males and 39 females. Although similar in most baseline characteristics, the CD4 count was higher in females (375 vs 290 cells/μL). Fewer females initiated ritonavir-boosted regimens. The median duration on therapy before interruption or change was longer in males (10 versus 4 months) (odds ratio [OR] 1.40 95% confidence interval: 0.95–2.04; P = 0.09). HIV RNA suppression was frequent (74%) and mean CD4 count achieved robust (over 400 cells/μL) at 6 months, irrespective of sex. The primary reasons for therapy interruption in females and males included: gastrointestinal intolerance (25% vs 19%; P = 0.42); poor adherence (22% vs 15%; P = 0.31); neuropsychiatric symptoms (19% vs 5%; P = 0.003); and lost to follow-up (3% vs 13%; P = 0.08). Seven males (5%) and no females discontinued therapy for liver-specific complications. Death rate was higher in females (23% vs 7%; P = 0.003).Conclusion: There are subtle differences in the characteristics of female and male HIV–HCV coinfected patients that influence HIV treatment decisions. The reasons for treatment interruption and change differ by biological sex. This knowledge should be considered when starting HIV therapy and in efforts to improve treatment outcomes.Keywords: AIDS, HIV, HCV, coinfection, HAART, viral load, women, gender differences, outcome, CD4 cell counts