BACKGROUND: Raltegravir and maraviroc represent new, important resources for HIV-infected patients with intolerance or resistance to other antiretroviral agents. The safety and efficacy of both drugs have been investigated, but there is no information on possible pharmacokinetic interactions between these 2 drugs in clinical practice. OBJECTIVE: To evaluate raltegravir plasma concentrations in heavily treatment-experienced patients receiving salvage regimens and explore, in a preliminary assessment, the potential influence of maraviroc coadministration and other cofactors on raltegravir trough concentrations (C_trough). METHODS: Fifty-four HIV-infected patients with triple class (nucleoside reverse transcriptase inhibitor, nonnucleoside reverse transcriptase inhibitor, protease inhibitor) treatment experience starting raltegravir 400 mg twice daily, with (n = 11) or without (n = 43) concomitant maraviroc 300 mg twice daily, were evaluated. All regimens included at least 3 drugs of at least 2 different classes. Raltegravir plasma C_trough, after at least 1 month of treatment, were analyzed to compare groups of patients taking raltegravir only and raltegravir plus maraviroc. Immunovirological (CD4, HIV-RNA) and clinical data after 6 months of treatment were also collected and described. RESULTS: Raltegravir plasma C_trough showed a large variability (range <0.020-2.47 μg/mL). Median levels were similar in the 2 groups (raltegravir + maraviroc 0.104 μg/mL, range 0.025−0.826; raltegravir 0.090 μg/mL, range <0.020-2.47, p = 0.400). Detectable (>0.02 μg/mL) raltegravir concentrations were observed in all patients receiving raltegravir + maraviroc and in 74% of patients receiving raltegravir alone (p = 0.060). After 6 months of treatment, the 2 groups had similar clinical, virologic, and immunologic conditions. CONCLUSIONS: Coadministration of maraviroc does not seem to have any relevant effects on raltegravir plasma C_trough in heavily treatment-experienced patients receiving salvage regimens. Further studies should evaluate the potential additional benefits of maraviroc coadministration in terms of virologic and immunologic response.