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Fuzeon--Beneficial Despite Resistance?
Feb 14, 2006

Dr. Sherer, Is Fuzeon beneficial even when a patient is clearly resistant to it? My viral load dropped to 1800 after first month of treatment, then rose to more than 100,000 three months later. The high viral load has been reconfirmed.

Response from Dr. Sherer

In a small study that attempted to answer this question, the answer appeared to be yes, there is still value in taking Fuzeon, even in the presence of documented resistance. In this small study, there was substantial additional viremia when Fuzeon was discontinued, in spite of the evidence of drug resistance.

There are other examples of partial activity that might be useful here. Even with the M184V resistance mutation, for example, lamivudine (3TC) retains some antiviral activity, and it also offers benefits in terms of the reduced fitness of the virus.

Each resistance mutation 'costs' the virus something. Some resistance mutations, e.g. for the NRTIs, appear to cause significant reductions in viral replication capacity, i.e the ability of the virus to complete a single replication cycle in the laboratory. This lab test result is often used as a surrogate marker for the ability of the virus to cause disease progression, i.e. the virus 'fitness'.

So it may be that Fuzeon in your case is causing reduced viral fitness. Other information to look at to assess its value in your regimen, of course, include the CD4 cell count trends, the replication capacity of the virus (obtained by a phenotype test while you are taking your current regimen, including Fuzeon) and the discomfort to you causes by the inconvenience of twice daily injections, the injection site reactions (if any), and other quality of life issues.

I urge you to talk to your doctor about your questions and this response.

HAART vacation 2 months 0-242,000 v.l.; will 489 CD4s prevent mutations
Trizivir and Combivir

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