A comparison of phosphonoacetic acid and phosphonoformic acid activity in genital herpes simplex virus type 1 and type 2 infections of mice.

The activity of phosphonoacetic acid (PAA) and phosphonoformic acid (PFA) against four strains of herpes simplex virus type 1 (HSV-1) and four strains of HSV-2 were compared in tissue culture and in a murine model of genital herpes. In mouse embryo fibroblast cells, both drugs were three-fold more active against the HSV-1 strains than against the HSV-2 strains. In contrast, in the animal model infections, PAA appeared to be more active against the HSV-2 strains, while PFA was equally effective against both HSV types. In mice infected intravaginally with HSV-2 and treated with intravaginal 5% PAA, none of the treated mice became infected, replication of virus in the genital tract was completely inhibited, none of the infected mice died from encephalitis, and latent infection in lumbosacral ganglia of surviving animals was completely prevented. In HSV-1 genital infection treated with PAA, 20-60% of mice became infected, replication of virus in the genital tract was strikingly reduced, none of the infected mice died, and latent infection was completely prevented. In both HSV-2 and HSV-1 genital infections, 20-70% of animals treated with 8% PFA became infected, growth of virus in the genital tract was reduced significantly but not completely suppressed, mortality was variably altered, and there was a trend towards reduction in the frequently of latent infection. These results indicate that HSV-1 strains are more sensitive to PAA and PFA in tissue culture, but the HSV-2 strains are generally more amenable to therapy in the murine model of genital herpes. Although PAA appeared to be more active that PFA in the genital infection, both drugs significantly altered the course of the infection. Since dermal toxicity associated with PAA precludes its use in humans and since PFA is already undergoing trials in patients with recurrent herpes labialis, the current results suggest that topical PFA deserved further evaluation in the treatment of mucocutaneous HSV infections, including genital herpes.