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Biotech / Medical : Agouron Pharmaceuticals (AGPH) -- Ignore unavailable to you. Want to Upgrade?

To: JOHN W. who wrote (2835)	11/16/1997 6:47:00 AM
From: Henry Niman	Read Replies (3) \| Respond to of 6136

JOHN, The formation of a resistant virus is fairly straightforward. When new viruses are made, the gentic material is copied. The virus' enzyme for make new copies makes quite a few mistakes. Sometimes these mistakes produce a new protein that is resistant to the drug(s) being used ti kill the virus. The viruses without mistakes are killed, and soon the resistant ones are the dominant type. If the virus is in resting cells and there is no replication, then the virus doesn't make copies and no resistance develops. If the virus is dividing, then eventually there is resistance. The time for resistance is dependent on how many viruses there are to begin with as well as the rate of replication as well as the copy error rate. The two papers that came out last week show that there are non-dividing cells that harbor the virus. These viruses don't become resistant until cell division begins. The cells can be stimulated by foreign infectious agents. When that happens, the virus begins to replicate and the potential for resistance increases. The Fauci paper that has not been published yet, indicates that a low level of replication is going on, even when the virus is "undectable". Low levels of replication means that resistance takes longer, but it will happen eventually. Whether that eventually comes before or after the patient dies of something else is still an open question. I have said that PIs are good for the short term in most instances. I consider 2 years as short term. Theoretically, it really only takes 1 resistant virus. Current asssays can measure down to 500 copies per ml of blood. More senstive assays go down to 20 copies. However, even the more sensitive approaches do not look at each cell. They just look at levels in the blood. The virus may be hiding out in more reserviores than those tested in the most recent studies, so it is possible that the amount of replication is considerably more than that found in the isolated cells that were examined.