Defining Antiviral Potency: IC₅₀, IQ, and Dose Dependency

For several decades, the potency of antimicrobial agents has been measured primarily by the 50% inhibitory concentration (IC₅₀; the drug concentration that yields 50% of the maximum inhibitory effect) and the inhibitory quotient (IQ; the ratio of plasma drug concentration to IC₅₀). However, among the approved antiretrovirals, most IC₅₀ values are similar, and the IQ values, although more variable, overlap considerably, especially between PIs and NRTIs. Now, investigators explore the advantages and limitations of adding dose dependency to the definition of antiviral potency.

Dose dependency is calculated as the slope of the line obtained when drug concentration is plotted against antiviral activity. Unlike IC₅₀ and IQ values, dose-dependency …