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and Hepatitis.com Coverage of the
50th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC 2010)
Maraviroc Failure with Co-receptor Switch Does Not Lead to HIV Disease Progression
People with late-stage HIV disease are more likely to have CXCR4-tropic HIV -- though a recent study found that even in this group CCR5-tropic strains are most common -- and some research indicates that CXCR4-tropic strains are associated with faster disease progression.
S. Portsmouth from Pfizer and colleagues looked at long-term clinical consequences among people who experience a CCR5 to CXCR4 co-receptor tropism switch during treatment with maraviroc-containing regimens. Maraviroc prevents HIV from using the CCR5 co-receptor, so is only effective against CCR5-tropic virus.
People considering maraviroc receive a tropism test to ensure that they have exclusively CCR5-tropic HIV strains. But HIV can mutate to switch tropism, which sometimes happens in patients experiencing virological failure while taking CCR5 antagonists. This prompted concern that use of maraviroc might favor the more aggressive CXCR4-tropic strains.
Investigators conducted an analysis of 15 participants in the MERIT trial who experienced treatment failure on maraviroc and showed phenotypic evidence of co-receptor tropism change (4% of all maraviroc recipients). They looked at changes in CD4 cell count, response to subsequent therapy, and clinical events. The average duration of follow-up was 192 weeks (range 12-240 weeks).
MERIT included more than 700 treatment-naive participants who were randomly
assigned to receive either twice-daily maraviroc or once-daily efavirenz,
both in combination with zidovudine/lamivudine
previously reported, In an analysis of patients determined to have
only CCR5-tropic virus using the current more sensitive enhanced Trofile
tropism test, maraviroc and efavirenz were equally effective, but maraviroc
was associated with larger CD4 cell gains and fewer side effects.
"With extended follow-up, no adverse clinical consequences were observed following failure-associated emergence of CXCR4-using virus with maraviroc," the researchers concluded. "Subjects had good immunological outcomes and responded to subsequent therapy. Tropism reverted to [CCR5] in some patients after stopping maraviroc."
Investigator affiliations: Pfizer, New York, NY; Pfizer, Sandwich, UK; British Columbia Ctr for Excellence in HIV, Vancouver, Canada; Pfizer, New London, CT.