Question

Define therapeutic range/level and lethal dose. What units are associated with these
terms?

Answer 1

Therapeutic range/level refers to the dosage range or blood plasma concentration expected to attain the desired therapeutic effects. It is also known as the pharmaceutical window of a drug, the range of drug dosages that can effectively treat diseases without any toxic effects. It also indicates the drug concentration at which patients will experience the desired clinical effect with a minimum of adverse reactions. The size of the range is determined by the toxicity of the drug.

Lethal dose refers to the amount of the drug when administered to a human or an animal will prove fatal.

Units:

LD₅₀ refers to the standard measure of the toxicity of a material that will kill half of the sample population of a specific test animal in a specified period through exposure via ingestion, skin contact or injection. It is measured in micrograms or milligrams. ED₅₀ is the effective dose of the drug in 50% of the population. TD₅₀ indicates the toxic dose in 50% of the population.

In animal studies,

Therapeutic index = LD₅₀/ED₅₀

In humans,

Therapeutic index = TD₅₀/ED₅₀

where Therapeutic index or TI is the value of comparison of the amount of the therapeutic agent that causes therapeutic effect to the amount that causes toxicity.

The lethal concentration is given as LC₅₀.