ABSTRACT
It is suggested that (a) LD50 is the measure of the efficacy of antiviral drugs: (b) a disease is characterized by the "barrier" type of a pathological process when in pathogenesis there exists an event whose manifestation largely determines the outcome of a disease (recovery/severe form with a fatal outcome). If the event consists in the penetration of a pathogen into a susceptible cell and the consequent reproduction of an antigen, the value LD50 for man is expressed as the same parameter for a model animal and as the parameters determined by in vitro human and animal cell experiments. The parameters include the degree of viral production adsorption on the cell and the levels of its reproduction. The algorithms for evaluating the efficacy of viral drugs are based on the relationship. The adequacy of the relationship is illustrated by experimental findings.