What number determines the safety of a drug?

The therapeutic index is a critical pharmacological parameter that helps determine the safety of a drug. It is defined as the ratio between the toxic dose and the effective dose of a medication. A high therapeutic index indicates a wide margin between doses that produce the desired therapeutic effects and doses that could lead to toxic effects, suggesting that the drug is relatively safe for use. Conversely, a low therapeutic index suggests that there is a narrow margin between effective and toxic doses, indicating that careful monitoring and dosage adjustments may be necessary to avoid potential adverse effects.

In assessing drug safety, the therapeutic index provides essential information for clinicians and healthcare professionals in considering the risk-benefit ratio of a treatment. This makes it a fundamental concept in pharmacology when evaluating how safely a drug can be prescribed to patients.