## What is the scientific definition of half-life?

the time required for one half the atoms of a given amount of a radioactive substance to disintegrate. Also called biological half-life . the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.

What determines half-life?

Half-life (t1/2) is defined as the amount of time required for the drug concentration measured in plasma (or other biological matrices) to be reduced to exactly half of its starting concentration or amount. After IV dosing, the drug concentrations in plasma decline due to both elimination and distribution [15].

What is the best definition for the half-life of an element?

Explanation: The half-life of a radioactive isotope is the amount of time required for half of the radioactive atoms to decay.

### What is meant by the half-life of an isotope?

One important measure of the rate at which a radioactive substance decays is called half-life, or t1/2. Half-life is the amount of time needed for one half of a given quantity of a substance to decay. Half-lives as short as 10–6 second and as long as 109 years are common.

What are the two definitions for half-life?

Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve. Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube. The half-life of radioactive carbon-14 is 5,730 years.

What does half-life mean for drugs?

The half-life of a drug is the time it takes for the amount of a drug’s active substance in your body to reduce by half. This depends on how the body processes and gets rid of the drug. It can vary from a few hours to a few days, or sometimes weeks.

#### What is a half-life and how do you calculate a drug’s half-life?

Half-life (t½) is the time required to reduce the concentration of a drug by half. The formula for half-life is (t½ = 0.693 × Vd /CL) Volume of distribution (Vd) and clearance (CL) are required to calculate this variable.

How does half-life affect dosing?

In other words, after one half-life, the concentration of the drug in the body will be half of the starting dose. With each additional half-life, proportionately less of the drug is eliminated. However, the time required for the drug to reach half of the original concentration remains constant.

What is half-life in your own words?

1 : the time required for half of something to undergo a process: such as. a : the time required for half of the atoms of a radioactive substance to become disintegrated.

## Why do we use half-life and not full life?

Half-life steps onto the scene in the decay process. While the lifespan of any individual atom is random and unpredictable, the probability of decay is constant. That is, the rate of decay will slow in proportion to the amount of radioactive material you have.

How does half-life work for drugs?

Which is the best definition of biological half life?

The time required for half the nuclei of a specific radionuclide or radioactive substance to undergo radioactive decay.physical half-life. The time required for half the quantity of a drug or other substance deposited in a living organism to be metabolized or eliminated by normal biological processes.biological half-life.

### How is the half life of an atom defined?

Instead, the half-life is defined in terms of probability: “Half-life is the time required for exactly half of the entities to decay on average”. In other words, the probability of a radioactive atom decaying within its half-life is 50%.

What is the half life of a drug?

In biology and pharmacology. A biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity.

What is the half life of a distribution?

Distribution Half-Life. Distribution half-life is 0.5–1 hour in most patients, with a volume of distribution of 0.39–0.9L/kg;