['The relationship between lopinavir trough plasma concentration at baseline and virological efficacy 3 months after the beginning of the therapy was investigated in an unselected cohort of HIV-1-infected patients', 'According to initial trough lopinavir plasma level, patients were classified into three groups: the subtherapeutic group (<3 mg/L, n=18), the therapeutic group (between 3 and 8 mg/L, n=50) and the toxic group (>8 mg/L, n=16). The virological response after 3 months of lopinavir treatment, defined as a viral load <200 HIV-1 RNA copies/mL, was compared amongst these groups.', 'The virological response was significantly different (P<0.05) between the subtherapeutic group (22.% of patients with viral load<200 copies/mL) and the other groups (56.0% of patients with a viral load<200 copies/mL in the therapeutic group and 56.2% in the toxic group).'] Are low initial trough plasma concentrations of lopinavir associated with an impairment of virological response in an unselected cohort of HIV-1-infected patients?