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| | BioS 353 |
 | | Because there are typically about a hundred million or so virions in the body, we conclude that at any given time, there are thousands of virions in the body with the particular change, and thus these virions are already partially resistant to the drug before the patient starts taking it. |
 | | If the patient starts taking two drugs that require separate mutations to give partial resistance to each drug, the fraction of double-resistant virions already present in the body will be something like 1 in 10,000 times 1 in 10,000, which is 1 in a hundred million. |
 | | If the patient starts taking three drugs that each require separate mutations to give partial resistance to each drug, the fraction of triple-resistant virions already present in the body is expected to be something like 1 in a trillion (one in ten to 12'th power). |
| www.lehigh.edu /~jas0/V17.html (896 words) |
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