The major trials conducted on treatment simplifi cation included large portions of patients who had previously received monotherapy or dual therapy and were likely to have relevant mutations of resistance at baseline. These studies concluded that simplifi cation was safe (especially when this
population was excluded), with some additional risk of viral failure for subjects simplifi ed to abacavir- based regimens. On the other hand, induction-maintenance studies and other studies which involved only patients who had started HAART as the fi rst-line showed that simplifi cation to abacavir
was as safe as continuation of the original regimen and better accepted by the patients. The largest randomized studies of simplifi cation that allowed extrapolation of data on the population of subjects who had never received suboptimal therapy were reviewed. Four studies failed to show signifi cant differences in effi cacy between treatment arms, while two detected signifi cant differences in favor of the continuation arms. Simplifi cation to abacavir led to signifi cant decreases in cholesterol and triglyceride levels and to slight improvements in quality of life. No variations in body shape were detected, although the duration was probably insuffi cient and most studies
did not involve adequate technology (i.e. DEXA, CT). Other, smaller studies are also presented in the review, selected for their particular design or analysis, which may contribute to a better understanding of the setting in which simplifi cation may be a feasible option. Choosing the adequate timing and the correct patient characteristics, simplifi cation to abacavirbased
regimens is safe and prevents metabolic consequences of therapy.

Keywords: Dideoxynucleosides - adverse effects, Antiretroviral Therapy, Highly Active, Anti-HIV Agents - adverse effects, Drug Resistance, Viral - genetics, Drug Therapy, Combination, Drug Tolerance, HIV Infections - drug therapy, HIV-1 - genetics, Multicenter Studies as Topic, Mutation, Safety