Calculate therapeutic index from TD50 or LD50 and ED50, or solve for a missing dose value with mg, g, µg, and kg unit options and view interpretation.
Therapeutic Index Formula
The following formula is used to calculate the Therapeutic Index.
Variables:
- TI is the Therapeutic Index
- TD50 is the median toxic dose
- ED50 is the median effective dose
To calculate the TD50-based Therapeutic Index, divide the median toxic dose by the median effective dose using matching dose units. The LD50-based option instead divides median lethal dose by ED50. Compare endpoints for the same substance, species or population, route and dose basis. The ratio alone does not establish clinical safety or determine a patient dose.
What is a Therapeutic Index?
A Therapeutic Index (TI) commonly compares a median adverse-effect dose with a median effective dose. Here, TD50 is a defined toxic endpoint in 50% of the tested population, LD50 is a lethal endpoint in 50%, and ED50 is the dose effective in 50%. A larger ratio indicates greater separation of these particular endpoints; it does not provide a universal narrow/wide classification, predict an individual’s response or replace drug-specific clinical evidence.
How to Calculate Therapeutic Index?
The following steps outline the TD50-based index. Choose the desired solve task in the calculator; LD50 tasks use the median lethal endpoint instead. All dose endpoints and the ratio must be positive.
- First, determine the median toxic dose (TD50).
- Next, determine the median effective dose (ED50).
- Next, gather the formula from above: TI = TD50 / ED50.
- Finally, calculate the Therapeutic Index (TI).
- After inserting the values for TD50 and ED50 and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following variables as an example problem to test your knowledge:
TD50 (median toxic dose) = 50 mg
ED50 (median effective dose) = 10 mg; TI = 50 / 10 = 5 (dimensionless).
