Plaque inhibition assay for drug susceptibility testing of influenza viruses

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Abstract
The relative antiviral activities of 4 drugs against contemporary strains of influenza A and B viruses were determined in Madin-Darby canine kidney cell monolayers with a plaque inhibition assay. This assay proved to be a reliable, rapid method of determining 50% inhibitory concentrations that correlated well with clinically achievable drug levels and the results of clinical trials. Contemporary strains of influenza A viruses (subtypes H1N1, H3N2, HSW1N1) required amantadine hydrochloride and rimantadine hydrochloride 50% inhibitory concentrations in the range of 0.2-0.4 .mu.g/ml, whereas 50% inhibitory concentrations ranged from .apprx. 50-100 .mu.g/ml against influenza B viruses. Ribavirin was approximately 10-fold less active than amantadine hydrochloride against influenza A viruses, and the ribavirin 50% inhibitory concentrations against both influenza A and B viruses ranged from 2.6-6.8 .mu.g/ml. Inosiplex had no antiviral activity in this test system.