DESCRIPTION R-77975's predecessor, R 61837, a substituted phenyl-pyridazinamine, was effective in inhibiting 80% of 100 serotypes tested (EC80) at concentrations above 32 micrograms/ml, pirodavir inhibits the same percentage of viruses at 0.064 micrograms/ml. Pirodavir is also effective in inhibiting 16 enteroviruses, with an EC80 of 1.3 micrograms/ml. Pirodavir acts at an early stage of the viral replication cycle (up to 40 min after infection) and reduces the yield of selected rhinoviruses 1,000- to 100,000-fold in a single round of replication.
Adults with symptoms of < or = 2 days' duration were randomly assigned to intranasal sprays of pirodavir (2 mg per treatment) or placebo six times daily for 5 days. In people with laboratory-documented rhinovirus colds (53 in the pirodavir group, 55 in the placebo group), no significant differences in the resolution of respiratory symptoms were apparent between the groups. The median duration of illness was 7 days in each group. Similarly, scores for individual symptoms found no differences in favor of pirodavir during or after treatment. (BOC Sciences Bioactive Compounds)