The maximum concentration at the splenic flexure was reached 10 h after the first dose and was 49-fold higher than blood plasma. C 12h was similar to concentration in the terminal ileum (59 vs. 64 μg/ml). Following multiple doses, the AUC0-12h increased from 258 to 2240 μg*h/ml, which was approximately 650-fold higher than blood plasma. Raltegravir accumulated in the area of the splenic flexure more than any other area within the GI tract following multiple doses (accumulation ratio = 8.7).
Previous investigations by our group and others have shown wide variability in colorectal tissue penetration reinforcing that assumptions between specific antiretroviral agents or classes cannot be made. In HIV-negative men, darunavir exposure in rectal tissue is 2.7-fold higher than blood plasma . The CCR5 antagonist maraviroc exposure in rectal tissue is even higher: nine-fold following a single dose and 27-fold higher than blood plasma following multiple doses . Following multiple doses, etravirine exposure is two-fold higher than blood plasma . The wide variability in exposure between drugs with similar mechanisms of action and within the same tissue is exemplified in the NRTIs tenofovir and emtricitabine. In rectal tissue, tenofovir exposures are 46-fold higher whereas emtricitabine exposures are 2.6-fold higher than blood plasma following a single dose .
The reported concentrations are dependent on the methods in which the antiretroviral agents are being measured. For example, low or sub-therapeutic concentrations of atazanavir, tenofovir, and emtricitabine were found in isolated mononuclear cells from the colorectal tissue of five HIV-infected men [30,31]. In contrast our previous [23,24,29,32] and current work quantifies the drug of interest in homogenized tissue. Others have measured intracellular concentrations of raltegravir from peripheral blood mononuclear cells using methods similar to intracellular reverse transcriptase inhibitors [33,34]. However, underestimation of drug concentrations may result from analyzing specific cells from colonic tissue due to the difficulty in obtaining sufficient quantities of in-vivo tissue required to accurately identify and isolate enough cells. In contrast, the use of tissue homogenates may result in an overestimation in drug exposure, as both intracellular and extracellular concentrations are being measured. These studies emphasize the importance in developing standard methods for measuring drug concentrations in specific matrices in order to expedite research priorities such that results across investigations can be compared and target concentrations based on specific objections (e.g. eradication, treatment, or prevention) can be determined.
Furthermore, a mechanism by which efficacy of potential strategies is easily quantified and reflective of all lymphoid tissue is essential. Rigorous investigations following antiretroviral intensification with raltegravir demonstrate the lack of effect on low-level plasma viremia [39–42], which may not reflect alterations elsewhere in the body. For example, seven HIV-infected individuals were noted to have a reduction in proviral DNA in GALT following raltegravir intensification . In acutely infected individuals in which there is rapid depletion of active CD4+ T cells, the prompt initiation of ‘megaART’ – including raltegravir and the CCR5-receptor agonist maraviroc to standard ART – results in a reduction in HIV DNA from rectal tissue . Similarly, the marked reduction of rectal tissue HIV DNA in rhesus macaques with chronic simian immunodeficiency virus is also seen with the addition of raltegravir and maraviroc to standard ART . Depending on the application, as this investigation found, targeting different areas of the colon (e.g. GALT vs. colorectal tissue) may be necessary to make precise measures of drug exposure and determine subsequent pharmacokinetic predictors of drug efficacy.
The authors appreciate the efforts of the UNC Gastrointestinal Procedure nurses in coordinating the precise timing of colonoscopies.
Supported in part by National Institutes of Health grants R37 DK49381 (M.S.C.), R34 AI087065 (A.D.M.K.), K23 AI773355 (K.B.P.), U01 AI095031 (A.D.M.K.), P30 AI50410 (UNC Center for AIDS Research), and UL1 RR025747 (UNC TraCS Clinical Translational Research Center). Supported in part by the Merck Investigator Initiated Research Program. Rectal sexually transmitted disease screening was performed in the Microbiology Core Laboratory of the Southeastern Sexually Transmitted Infections Cooperative Research Center under the direction of Dr Marcia Hobbs and supported by NIH grant U19 AI31496.
Author Contributions: K.B.P., M.S.C. and A.D.M.K. conceived and designed the experiments. H.A.P. and T.S. coordinated the specimen collections. N.J.S., E.S.D., R.D.M. performed the colonoscopies and obtained the biopsy specimens. S.J. analyzed the specimens. K.B.P. and A.D.M.K. analyzed the data. K.B.P. and A.D.M.K. created the presentation of some of the data for the 13th International Workshop on Clinical Pharmacology of HIV Therapy April 16–18, 2012 Barcelona, Spain. K.B.P. and A.D.M.K. wrote the article. All authors reviewed the article.
K.B. P. and A.D.M.K. have received investigator initiated research grants from Merck and GlaxoSmithKline. The remaining authors have no competing interests.
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