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Page 478<br />

lished—was associated with inhibition of virus replication. However viral titer was higher (1.3 log 10<br />

compared to 4.0 log 10 at 10 mg/mL concentration of the drug) for the delayed administration compared<br />

with viral titer when the drug was present throughout the period of viral exposure. The clinical<br />

significance of this in the treatment of established infections has yet to be explored in detail, although<br />

preliminary clinical trails [98] have indicated some positive results.<br />

B. Administration and Inhibition In Vivo<br />

The earlier work of Palase and Schulman [77] indicated that the failure in inhibiting viral replication in<br />

mice after intranasal and subcutaneous treatment with Neu5aC2en would also occur for Neu5Ac2en<br />

analogs. This failure of Neu5Ac2en as an antiviral treatment in animal models can now be ascribed to<br />

the rapid excretion of the compound [99] there<strong>by</strong> not delivering sufficient concentration of the inhibitor<br />

to the infected tissue. It had been shown [91] that the antiviral activity in mice is considerably more,<br />

when the 4-guanidino compound is administered intranasally than when the drug is injected<br />

intraperitoneally. This can be attributed to the localization of sufficiently high concentration of inhibitor<br />

in the lining of the nasal and respiratory epithelia where influenza virus replication is believed to occur.<br />

Animal trials with ferrets challenged with influenza virus have shown the 4-guanidino Neu5Ac2en<br />

compound is effective in studies [91] involving prophylactic administration of the drug. When the drug<br />

is administrated intranasally, 50 μg/kg, twice daily, one day before infection with the virus and the<br />

succeeding six days, it substantially reduces virus titer in nasal washing and abolishes fever that usually<br />

appears 3 days after infection.<br />

The drug is currently undergoing clinical trials, and the initial results from a double blind, randomized,<br />

placebo-controlled trial using this compound have been positive both for early treatment and<br />

prophylaxis of experimental inoculation of human volunteers [98] with influenza A/Texas/91.<br />

C. <strong>Drug</strong> Resistance<br />

Although the active site of influenza virus has been conserved in all known field strains of the virus, the<br />

possibility of drug resistance needs to be addressed. Experience with influenza and other viruses, in<br />

particular HIV, have shown [100] that drug-resistant mutants arise very rapidly, resulting in the<br />

effectiveness of antiviral drugs being short lived. One attempted solution to the problem is the use of<br />

several drugs during therapy [101], making it more difficult for the virus the develop resistance.<br />

In the case of influenza virus, there have to date been no reports of drug resistance from field strains.<br />

However it has recently been reported [102,103]<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_478.html [4/9/2004 12:27:14 AM]

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