Experimental encephalitis caused by herpes simplex virus: comparison of treatment with tilorone hydrochloride and phosphonoacetic acid.

A mouse model of encephalitis caused by herpes simplex virus was used to compare the antiviral activity of tilorone hydrochloride with that of phosphonoacetic acid. These compounds were also administered simultaneously to determine whether the combination had a synergistic effect. Rates of survival and concentrations of virus in brain were used as criteria for judging the effectiveness of treatment. The fatal course of encephalitis was not altered by any treatment protocols in which tilorone hydrochloride was used alone. Four days of treatment with phosphonoacetic acid resulted in a long-term survival rate of about 15% of the infected, treated animals, and extension of this therapy for an additional three days resulted in an overall survival rate of about 35%. No increase in survival rate was obtained by use of phosphonoacetic acid and tilorone hydrochloride in combination. The concentration of virus in the brains of tilorone hydrochloride treated animals did not differ significantly from that in the untreated, infected control animals. Treatment with phosphonoacetic acid resulted in a reduction in titer of virus in brain and in an increased rate of survival.