Effective Dose

The term effective dose is used in conjunction with drug dosing or radiation dosing. The exact meaning varies depending on the context.

In radiation safety, the term effective dose was coined by the International Commission on Radiological Protection. It does not refer to an exact quantity but is calculated by multiplying actual organ doses by weighted risk factors that are related to an individual organ's radiosensitivity for developing cancer. The sum of the products is called the effective whole-body dose or the effective dose. Tissue-weighting factors can vary from 0.01 for skin, or 0.05 for thyroid, to 0.20 for the gonads.

In reference to a pharmacologic agent, the effective dose of the agent is the dose that produces a response considered “effective” as defined by the study protocol or clinical response. It may represent a cure of a disease or a mitigation of symptoms.

When considering a “dose–response” curve, different effective doses can be defined. The effective dose (50), or ED50 is the effective dose in 50% of the patients or subjects. The ED95 represents the effective dose in 95% of patients or subjects.

Because each patient is unique in the way he or she responds to a given drug, to arrive at an effective dose [Page 149]researchers must consider many factors. The dose of a medication may need to be adjusted to compensate for age, gender, pregnancy, pharmacogenetic phenotype, kidney function, liver function, concurrent medications, concurrent diseases, and prior adverse drug reactions or drug allergies.