half-life


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half-life

 [haf´līf″]
the time required for the decay of half of a sample of particles of a radionuclide or elementary particle; see also radioactivity. Symbol t½ or T½.

half-life

(haf'līf),
The period in which the radioactivity or number of atoms of a radioactive substance decreases by half; similarly applied to any substance, such as a drug in serum, whose quantity decreases exponentially with time. Compare: half-time.

half-life

(hăf′līf′, häf′-)
n.
1. Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
2. Biology
a. 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. Also called biological half-life.
b. The time required for the radioactivity of material taken in by a living organism to be reduced to half its initial value by a combination of biological elimination processes and radioactive decay.
The amount of time required for a substance to be reduced to one-half of its previous level by degradation and/or decay (radioactive half-life), by catabolism (biological half-life), or by elimination from a system (e.g., serum half-life)
Haematology The time that cells stay in the circulation—e.g., red blood cells, 120 days, which increases after splenectomy; platelets, 4–6 days; eosinophils, 3–7 hours; neutrophils, 7 hours
Immunology The time an immunoglobulin stays in the circulation: 20–25 days for IgG, 6 days for IgA, 5 days for IgM, 2–8 days for IgD, 1–5 days for IgE
Nuclear medicine The length of time required for a radioisotope to decay to one-half of the original amount having the same radioactivity; a radioisotope’s effective T1/2 is either the time of decay—physical T1/2—or the time to elimination from a biological system. See Biological half-life
Physiology The time that it takes for half of a molecule’s activity to decay
Research See Cited half-life, Citing half-life
Therapeutics The amount of time it takes for the serum concentration of a drug to fall 50%, which reflects its rate of metabolism and elimination of parent drug and metabolites in the urine and stool

half-life

T1/2 The amount of time required for a substance to be reduced to one-half of its previous level by degradation and/or decay–radioactive half-life, by catabolism–biological half-life, or by elimination from a system–eg, half-life in serum Hematology The time that cells stay in the circulation–eg, RBCs 120 days–which ↑ after splenectomy, platelets–4-6 days, eosinophils–3-7 hrs, PMNs–7 hrs Immunology The time an Ig stays in the circulation: 20-25 days for IgG, 6 days for IgA, 5 days for IgM, 2-8 days for IgD, 1-5 days for IgE Therapeutics The time that a therapeutic agent remains in the circulation, which reflects its rate of metabolism and elimination of parent drug and metabolites in the urine and stool. See Effective half-life.
Half life in hours
Drug  Adult  Children
Digoxin  6–51  11–50
Gentamycin  2-3
Lithium 8–35
Phenobarbital  50–150  40–70
Phenytoin 18–30  12–22
Procainamide  2–4
Quinidine  4–7
Theophylline  3–8  1–8
Tobramycin  2–3
Valproic acid  8–15
Advance/Lab Feb 1995, p19  

half-life

(haf'līf)
1. The period in which the radioactivity or number of atoms of a radioactive substance decreases by half; similarly applied to any substance whose quantity decreases exponentially with time.
Compare: half-time
2. Time required for the serum concentration of a drug to decline by 50%.
Half-lifeclick for a larger image
Fig. 188 Half-life . X = half-life. Note that the time taken to reach zero amount is not 2 x X.

half-life

the time required for half of the mass of a radioactive substance to disintegrate. For example, the half-life of 14C is 5,700 years.

Half-life

The time required for half of the atoms in a radioactive substance to disintegrate.

half-life

(haf'līf)
1. The period in which the radioactivity or number of atoms of a radioactive substance decreases by half; similarly applied to any substance whose quantity decreases exponentially with time.
Compare: half-time
2. Time required for the serum concentration of a drug to decline by 50%.
References in periodicals archive ?
Furthermore, patients with blood Group O showed significantly shorter FVIII half-life than patients with non-O blood group (9.40 [+ or -] 0.68 h vs.
This morning, Laidlaw's NDA expired and he released a piece of "fanfiction" which, with a bit of guessing, you can read as the conclusion to the Half-Life games.
Many other fans of the franchise couldn't help but speculate that the new updates could be hinting at the possible release of "Half-Life 3." Since the release of the updates, many have been writing comments on Steam claiming that these could be the sign that "Half-Life 3" is coming soon.
Although the animal data, molecular weight (about 868), and elimination half-life (about 26 hours) suggest embryo-fetal risk, the high plasma protein binding (99.9%) should limit the amount crossing the placenta.
CSTD collected under the Global Monitoring Plan of the Stockholm Convention (Secretariat of the Stockholm Convention 2016) can also be evaluated with these models, which (unlike the CSTD half-life tool) can accommodate transgenerational transfer and changes in body weight and lipid weight with age (Table 1, dynamic PPK model) and are not restricted to biomonitoring data from the post-ban period.
Black Mesa started out as a Half-Life: Source mod almost a decade ago, with a playable (but unfinished) version being released in 2012.
a half-life / of a half-life a mean lifetime / of a mean lifetime
Parasite clearance half-life was then determined using serial blood smears.
Novozymes' VELTIS technology represents a series of engineered human albumins that in combination with a drug candidate, offers the potential for control of the therapeutic half-life, which allows for reducing the dosing frequency of drugs from daily to every two weeks or monthly.
What's more, once it is produced, Orb2A quickly falls apart; the protein has a half-life of only about an hour.
The first commercial product epoetin has a plasma half-life of only 6-8 h [7] in humans.
A search on the Internet will reveal that estimates for the half-life of an engineering career range from a couple of years to as many as 15 years.