To evaluate the relationship between plasma and intracellular darunavir (DRV) concentrations and virological efficacy in HIV-infected patients on DRV/rtv monotherapy.

To be enrolled, subjects had a plasma HIV-RNA <50 copies/mL for at least 6 months based, virologic failure while on a PI-containing regimen was allowed if the genotypic resistance tests showed no major resistance mutation associated to reduced susceptibility to DRV/rtv according to the International AIDS Society. Patients with transitory episodes of detectable plasma HIV-RNA viral load ("blip") preceded and followed by a plasma viral load <50 copies/mL without changes in antiretroviral treatment could also been included. The only exclusion criteria were pregnancy, hepatitis B coinfection and the concomitant use of drugs with potential major interactions with DRV/rtv pharmacokinetics.

Inclusion Criteria:

• Older than 18 years, starting an antiretroviral regimen based on darunavir-ritonavir (800/100 mg) once daily monotherapy between June 2010 and September 2010
• Plasma RNA-VIH < 50 copies/ml on stable antiretroviral treatment for ≥ 6 months
• Absence of resistance mutations in the protease gene, based on treatment history and/or genotypic resistance testing. that would decrease darunavir susceptibility

Exclusion Criteria:

• Pregnancy
• Chronic B hepatitis
• Genotypic resistance tests with evidence of resistance mutations in the protease gene that would decrease darunavir susceptibility
• Concomitant use of drugs with potentially adverse interactions with darunavir-ritonavir pharmacokinetics, such as rifampin

HIV-infected patients who started an antiretroviral regimen based on darunavir-ritonavir (800/100 mg) once daily monotherapy between June 2010 and September 2010