ORIGINAL INVESTIGATION Treatment Modification in Human Immunodeficiency Virus–Infected Individuals Starting Combination

Background: Adverse effects of combination antiret-roviral therapy (CART) commonly result in treatment modification and poor adherence. Methods: We investigated predictors of toxicity-related treatment modification during the first year of CART in 1318 antiretroviral-naive human immunode-ficiency virus (HIV)–infected individuals from the Swiss HIV Cohort Study who began treatment between Janu-ary 1, 2005, and June 30, 2008. Results:The total rate of treatmentmodificationwas 41.5 (95 % confidence interval [CI], 37.6-45.8) per 100 person-years. Of these, switches or discontinuations because of drug toxicity occurred at a rate of 22.4 (95 % CI, 19.5-25.6) per 100 person-years. The most frequent toxic ef-fects were gastrointestinal tract intolerance (28.9%), hy