If TI equals 10, what is the relationship between TD50 and ED50?

If TI equals 10, what is the relationship between TD50 and ED50?

• A. TD50 = ED50
• B. TI cannot be determined from that
• C. TD50 is ten times ED50
• D. TD50 is one-tenth of ED50

Answer: (C)

Therapeutic index is the ratio of the toxic dose that affects 50% of the population to the effective dose that produces the desired effect in 50% of the population. In symbols, TI = TD50 / ED50. If TI equals 10, then TD50 = 10 × ED50. That means the dose causing toxicity at 50% of people is ten times higher than the dose that achieves the desired therapeutic effect, indicating a relatively wide safety margin.

Therapeutic index is the ratio of the toxic dose that affects 50% of the population to the effective dose that produces the desired effect in 50% of the population. In symbols, TI = TD50 / ED50. If TI equals 10, then TD50 = 10 × ED50. That means the dose causing toxicity at 50% of people is ten times higher than the dose that achieves the desired therapeutic effect, indicating a relatively wide safety margin.