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Oct 31, 2008

My viral load has become detectable and my doctor would like to put me on Maraviroc and Isentress. I have been reviewing both of these drugs and I have some concerns with Maraviroc. I know it works on the CCR5 but what is known about the CCR5 receptor site? It would seem this drug should be used earlier in treatment but the naive data didn't show good results. Thanks for any help.

Response from Dr. McGowan

The CCR5 receptor is a receptor on the CD4 T cell. It is used as a 2nd (or co-) receptor for HIV to enter the T cell. HIV may also use another co-receptor (called CXCR4) to enter the cell. Since maraviroc only blocks virus that use CCR5, it is important to know what type of virus you have before you would use this drug. It has no activity versus virus that use CXCR4. A tropism test must be used to determine the type of virus a person carries. It is true that in the early stages of infection, the likelihood of having a CCR5 using virus is higher than in later stages, but even in later stages about half of people still have an CCR5 virus. Recently the tropism test has been improved to be more sensitive in detecting CXCR4 virus, so that the test is more reliable than it used to be. This should improve the repsponses to maraviroc since only people who are likely to benefit will get the drug. The naive trial you mention showed that Maraviroc did less well than efavirenz (Sustiva), but the study was done with the old tropism test. When this study was recently re-analysed using the newer, more sensitive assay, the 2 drugs worked equally well. I hope this addresses some of your concerns.

Best, Joe

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