Use Selectivity Ratio when you need to quantify drug selectivity as the off-target IC50 divided by the on-target IC50, where larger values indicate a more selective compound. Enter On-target IC50 and Off-target IC50 using the definitions and units below so the result can be reproduced.

On-target IC50

IC50 against the intended target, in nanomolar; must be greater than zero.

Off-target IC50

IC50 against the off-target, in nanomolar; must be greater than zero.

The published tool contract uses this rule: Quantify drug selectivity as the off-target IC50 divided by the on-target IC50, where larger values indicate a more selective compound.

Selectivity ratio

Off-target IC50 divided by on-target IC50.

A ratio or percentage can conceal the scale of its numerator and denominator and becomes sensitive to measurement error when the denominator is small.

Retain the original On-target IC50 and Off-target IC50 values and their units alongside the result. Selectivity Index is useful when you instead need to compute the ratio of toxic IC50 to therapeutic IC50 for a compound. APTT Ratio provides another view by helping you compute the activated partial thromboplastin time ratio as the patient APTT divided by the control APTT.

• Selectivity Index

  Compute the ratio of toxic IC50 to therapeutic IC50 for a compound.

• APTT Ratio

  Compute the activated partial thromboplastin time ratio as the patient APTT divided by the control APTT.

• a/A Ratio

  Compute the arterial-to-alveolar oxygen ratio as PaO2 divided by the alveolar oxygen tension from the simplified alveolar gas equation.