How is the therapeutic index (TI) calculated?

The therapeutic index (TI) is an important measure in pharmacology that indicates the safety of a drug. It is defined as the ratio of the lethal dose for 50% of the population (LD50) to the effective dose for 50% of the population (ED50). This calculation provides insight into the margin of safety of a medication; a higher TI suggests that there is a greater difference between the effective dose and the dose that could be harmful, making the drug safer for use.

In this context, the formula LD50 / ED50 is used to quantitatively assess how much more concentrated or potent the lethal effect is compared to the effective effect. If the TI is greater than 1, it indicates a safer profile, as the effective dose required for therapeutic purposes is significantly lower than that which causes lethality. This relationship is crucial for healthcare providers to consider when prescribing medications, as it helps gauge the potential risk versus the benefit of a drug treatment.

The other options present alternative calculations that do not accurately reflect the proper therapeutic index formula. The effective dose and maximum dose do not provide a proportionate measurement of safety. Similarly, the safety margin relative to the effective dose does not yield the classic therapeutic index used in pharmacological assessments. Therefore