Innovation Pharmaceuticals Inc (IPIX)

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Calculating the Average Selectivity Index (SI)


The selectivity index (SI) is a ratio that measures the window between cytotoxicity and antiviral activity by dividing the given AVA value into the TOX value (AVA/TOX). The higher the SI ratio, the theoretically more effective and safe a drug would be during in vivo treatment for a given viral infection.

The ideal drug would be cytotoxic only at very high concentrations and have antiviral activity at very low concentrations, thus yielding a high SI value (high AVA/low TOX) and thereby able to eliminate the target virus at concentrations well below its cytotoxic concentration.

The selectivity index of a compound is a widely accepted parameter used to express a compound’s in vitro efficacy in the inhibition of virus replication.