Antiretroviral tissue penetration ratios (TPRs) into small and large intestinal tissue. TPRs represent the extent of drug exposure in a given tissue relative to plasma and are calculated by dividing the tissue concentration (converted to ng/g) by a paired plasma concentration (ng/mL) using an assumed tissue density of 1.06 g/mL. A, Tenofovir (TFV) and emtricitabine TPRs were not significantly different across dosing cohorts in either the duodenum or rectum (P > .05); therefore, the TPRs for these 2 drugs were pooled when making further comparisons. Maraviroc (MVC) TPRs between the MVC and MVC + raltegravir (RAL) cohort were not significantly different and these values were also pooled. Significantly higher TFV penetration was observed in the duodenum compared to the colon, and MVC penetration was higher in the rectum vs the duodenum (*P = .001 for both). B, Tissue concentrations as reported in were individually compared to the highest 50% inhibitory concentration (IC₅₀) reported in the literature (IC₉₀ for efavirenz) after converting reported nM IC values to ng/mg. Tissue drug concentrations were above the IC₅₀ nearly 100% of the time. These TPRs are consistent with what has been observed in previous studies of gut tissue, except for RAL, which was lower than what has been previously reported []. C and D, All drug penetration vs human immunodeficiency virus (HIV) decreases from baseline: No correlation was observed between tissue levels of viral decay assayed from biopsy specimens collected after 9 months of combination antiretroviral therapy. C, HIV DNA was measured in single-cell suspensions of rectal and duodenal tissue biopsies. D, HIV RNA was measured from rectal and duodenal tissue homogenates. Tissue penetration ratios are shown in (A). Abbreviations: FTC, emtricitabine; MVC, maraviroc; NNRTI, nonnucleoside reverse transcriptase inhibitor; RAL, raltegravir; TFV, tenofovir.