Effect of treatment with 1-beta-D-arabinofuranosylthymine of experimental encephalitis induced by herpes simplex virus in mice.

1-beta-D-Arabinofuranosylthymine (ara-T) was examined for its therapeutic efficacy against encephalitis in mice inoculated intracerebrally with herpes simplex virus. Intraperitoneal treatment with 100 mg of ara-T per kg twice daily for 4.5 days was as effective as treatment with 50 mg of arabinosyladenine 5'-monophosphate per kg. Under the same conditions, doses of 5-iododeoxyuridine or arabinosylcytosine (50 mg/kg each) were not effective. Even when the virus inoculum was as high as 320 or 3,200 50% lethal doses, ara-T increased the life span significantly. Oral treatment with 27 mg of ara-T per kg produced a modest increase in the mean survival time, equal to that of 50 mg of ara-T per kg administered intraperitoneally or subcutaneously. A single dose of ara-T, 800 mg/kg intraperitoneally or 400 mg/kg orally, was effective. The 50% lethal dose of ara-T administered intraperitoneally and that administered orally were more than 10 and 15 g/kg, respectively. The therapeutic indexes (maximal tolerated dose divided by minimal effective dose) in multiple intraperitoneal treatments and in multiple oral treatments were estimated to be more than 25 and 100, respectively.